This information is intended for use by health professionals

1. Name of the medicinal product

Letrozole 2.5 mg film-coated tablets

2. Qualitative and quantitative composition

Each tablet contains 2.5 mg letrozole.

Excipient with known effect: each tablet contains 61.5 mg lactose monohydrate.

For a full list of excipients, see section 6.1.

3. Pharmaceutical form

Film-coated tablet.

Yellow film-coated round biconvex tablets, debossed with L9OO on one side and 2.5 on the other side.

4. Clinical particulars
4.1 Therapeutic indications

• Adjuvant treatment of postmenopausal women with hormone receptor positive invasive early breast cancer.

• Extended adjuvant treatment of hormone-dependent-invasive breast cancer in postmenopausal women who have received prior standard adjuvant tamoxifen therapy for 5 years.

• First-line treatment in postmenopausal women with hormone-dependent advanced breast cancer.

• Advanced breast cancer in women with natural or artificially induced postmenopausal endocrine status after relapse or disease progression, who have previously been treated with anti-oestrogens.

• Neo-adjuvant treatment of postmenopausal women with hormone receptor positive, HER-2 negative breast cancer where chemotherapy is not suitable and immediate surgery not indicated.

Efficacy has not been demonstrated in patients with hormone-receptor negative breast cancer.

4.2 Posology and method of administration


Adult and elderly patients

The recommended dose of letrozole is 2.5 mg once daily. No dose adjustment is required for elderly patients.In patients with advanced or metastatic breast cancer, treatment with letrozole should continue until tumour progression is evident.

In the adjuvant and extended adjuvant setting, treatment with letrozole should continue for 5 years or until tumour relapse occurs, whichever is first.

In the adjuvant setting a sequential treatment schedule (letrozole 2 years followed by tamoxifen 3 years) could also be considered (see sections 4.4 and 5.1).

In the neoadjuvant setting, treatment with letrozole could be continued for 4 to 8 months in order to establish optimal tumour reduction. If the response is not adequate, treatment with letrozole should be discontinued and surgery scheduled and/or further treatment options discussed with the patient.

Paediatric population

Letrozole is not recommended for use in children and adolescents. The safety and efficacy of letrozole in children and adolescents aged up to 17 years have not been established. Limited data are available and no recommendation on a posology can be made.

Renal impairment

No dosage adjustment of letrozole is required for patients with renal insufficiency with creatinine clearance ≥10ml/min.Insufficient data are available in cases of renal insufficiency with creatinine clearance lower than 10ml/min (see sections 4.4 and 5.2).

Hepatic impairment

No dose adjustment of letrozole is required for patients with mild to moderate hepatic insufficiency (Child-Pugh A or B). Insufficient data are available for patients with severe hepatic impairment. Patients with severe hepatic impairment (Child-Pugh C) require close supervision (see sections 4.4 and 5.2).

Method of administration

Letrozole should be taken orally and can be taken with or without food.

4.3 Contraindications

Letrozole is contraindicated in:

• Patients with known hypersensitivity to letrozole or to any of the excipients listed in the section 6.1.

• Premenopausal endocrine status

• Pregnancy; breast-feeding (see section 4.6)

4.4 Special warnings and precautions for use

Menopausal status

In patients whose menopausal status is unclear, luteinising harmone (LH), follicle stimulating hormone (FSH) and/or oestradiol levels should be measured before initiating treatment with letrozole. Only women of postmenopausal endocrine status should receive letrozole.

Renal impairment

Letrozole has not been investigated in a sufficient number of patients with a creatinine clearance lower than 10 ml/min. The potential risk/benefit to such patients should be carefully considered before administration of letrozole.

Hepatic impairment

In patients with severe hepatic impairment (Child-Pugh C), systemic exposure and terminal half-life were approximately doubled compared to healthy volunteers. Such patients should therefore be kept under close supervision (see section 5.2).

Bone effects

Letrozole is a potent oestrogen-lowering agent. Women with a history of osteoporosis and/or fractures, or who are at increased risk of osteoporosis, should have their bone mineral density formally assessed prior to the commencement of adjuvant and extended adjuvant treatment and monitored during and following treatment with letrozole. Treatment or prophylaxis for osteoporosis should be initiated as appropriate and carefully monitored. In the adjuvant setting a sequential treatment schedule (letrozole 2 years followed by tamoxifen 3 years) could also be considered depending on patient's safety profile (see sections 4.2, 4.8 and 5.1).

Other warnings

Co-administration of letrozole with tamoxifen, other anti-oestrogens or oestrogen-containing therapies should be avoided as these substances may diminish the pharmacological action of letrozole (see section 4.5).

Letrozole tablets contain lactose. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

4.5 Interaction with other medicinal products and other forms of interaction

Metabolism of letrozole is partly mediated via CYP2A6 and CYP3A4. Cimetidine, a weak, unspecific inhibitor of CYP450 enzymes, did not affect the plasma concentrations of letrozole. The effect of potent CYP450 inhibitors is unknown.

There is no clinically experience to date on the use of letrozole in combination with oestrogens or other anticancer agents, other than tamoxifen. Tamoxifen, other anti-oestrogens or oestrogen-containing therapies may diminish the pharmacological action of letrozole. In addition, co-administration of tamoxifen with letrozole has been shown to substantially decrease plasma concentrations of letrozole. Co-administration of letrozole with tamoxifen, other anti-oestrogens or oestrogens should be avoided.

In vitro, letrozole inhibits the cytochrome P450 isoenzyme 2A6 and, moderately, 2C19, but the clinical relevance is unknown. Caution is therefore indicated when giving letrozole concomitantly with medicinal products whose elimination is mainly dependent on these isoenzymes and whose therapeutic index is narrow (e.g. phenytoin, clopidogrel).

4.6 Fertility, pregnancy and lactation

Women of perimenopausal status or child-bearing potential

Letrozole should only be used in women with a clearly established postmenopausal status (see section 4.4). As there are reports of women regaining ovarian function during treatment with letrozole despite a clear postmenopausal status at start of therapy, the physician needs to discuss adequate contraception when necessary.


Based on human experience in which there have been isolated cases of birth defects (labial fusion, ambiguous genitalia), letrozole may cause congenital malformations when administered during pregnancy. Studies in animals have shown reproductive toxicity (see section 5.3).

Letrozole is contraindicated during pregnancy (see sections 4.3 and 5.3).


It is unknown whether letrozole and its metabolites are excreted in human milk. A risk to the newborns/infants cannot be excluded.

Letrozole is contraindicated during breast-feeding (see section 4.3).


The pharmacological action of letrozole is to reduce oestrogen production by aromatase inhibition. In premenopausal women, the inhibition of oestrogen synthesis leads to feedback increases in gonadotropin (LH, FSH) levels. Increased FSH levels in turn stimulate follicular growth, and can induce ovulation.

4.7 Effects on ability to drive and use machines

Letrozole has minor influence on the ability to drive and use machines. Since fatigue and dizziness have been observed with the use of letrozole and somnolence has been reported uncommonly, caution is advised when driving or using machines.

4.8 Undesirable effects

Summary of the safety profile

The frequencies of adverse reactions for letrozole are mainly based on data collected from clinical trials.

Up to approximately one third of the patients treated with letrozole in the metastatic setting and approximately 80% of the patients in the adjuvant setting as well as in the extended adjuvant setting experienced adverse reactions. The majority of the adverse reactions occurred during the first few weeks of treatment.The most frequently reported adverse reactions in clinical studies were hot flushes, hypercholesterolemia, arthralgia, fatigue, increased sweating and nausea.

Important additional adverse reactions that may occur with letrozole are: skeletal events such as osteoporosis and/or bone fractures and cardiovascular events (including cerebrovascular and thromboembolic events). The frequency category for these adverse reactions is described in Table 1.

The following adverse drug reactions, listed in Table 1 were reported from clinical studies and from post marketing experience with letrozole.

Table 1:Adverse reactions are ranked under headings of frequency, the most frequent first, using the following convention: very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), very rare (<1/10,000), not known (cannot be estimated from the available data).

Table 1: Adverse Reactions


Adverse reactions

Infections and infestations


Urinary tract infection

Neoplasms, benign, malignant and unspecified (including cysts and polyps)


Tumour pain1

Blood and the lymphatic system disorders



Immune system disorders

Not known:

Anaphylactic reaction

Metabolism and nutrition disorders

Very common:



Anorexia, appetite increase

Psychiatric disorders




Anxiety (including nervousness), irritability

Nervous system disorders


Headache, dizziness


Somnolence, insomnia, memory impairment, dysaesthesia (including paraesthesia, hypoesthesia), taste disturbance, cerebrovascular accident

Eye disorders


Cataract, eye irritation, blurred vision

Cardiac disorders


Palpitations1, tachycardia, ischaemic cardiac events (including new or worsening angina, angina requiring surgery, myocardial infarction and myocardial ischaemia)

Vascular disorders

Very common:

Hot flushes




Thrombophlebitis (including superficial and deep vein thrombophlebitis)


Pulmonary embolism, arterial thrombosis, cerebrovascular infarction

Respiratory, thoracic and mediastinal disorders


Dyspnoea, cough

Gastrointestinal disorders


Nausea, dyspepsia1, constipation, abdominal pain, diarrhoea, vomiting


Stomatitis1, dry mouth

Hepatobiliary disorders


Increased hepatic enzymes

Not known:


Skin and subcutaneous tissue disorders

Very common:

Increased sweating


Alopecia, rash (including erythematous, maculopapular, psoriaform, and vesicular rash), dry skin


Pruritus, urticaria

Not known:

Angioedema, toxic epidermal necrolysis, erythema multiforme

Musculoskeletal and connective tissue disorders

Very common:



Myalgia, bone pain1, osteoporosis, bone fractures



Renal and urinary disorders


Increased urinary frequency

Reproductive system and breast disorders


Vaginal bleeding


Vaginal discharge, vaginal dryness, breast pain

General disorders and administration site conditions

Very common:

Fatigue (including asthenia, malaise)


Peripheral oedema


General oedema, mucosal dryness, thirst, pyrexia



Weight increase


Weight loss

1Adverse drug reactions reported only in the metastatic setting.

Some adverse reactions have been reported with notably different frequencies in the adjuvant treatment setting. The following tables provide information on significant differences in letrozole versus tamoxifen monotherapy and in the letrozole-tamoxifen sequential treatment therapy:

Table 2: Adjuvant letrozole monotherapy versus tamoxifen monotherapy – adverse events with significant differences

Letrozole, incidence rate

Tamoxifen, incidence rate

Bone fracture

10.1% (13.8%)

7.1% (10.5%)


5.1% (5.1%)

2.7% (2.7%)

Thromboembolic events

2.1% (2.9%)

3.6% (4.5%)

Myocardial infarction

1.0% (1.5%)

0.5% (1.0%)

Endometrial hyperplasia/endometrial cancer

0.2% (0.4%)

2.3% (2.9%)

Note: Median duration of treatment 60 months. Reporting period includes treatment period plus 30 days after stopping treatment.

Percentages in parentheses indicate event frequencies any time after randomisation, including post study treatment period. Median follow-up was 73 months.

Table 3: Sequential treatment versus letrozole monotherapy – adverse events with significant differences

Letrozole monotherapy

Letrozole → >tamoxifen

Tamoxifen → >letrozole

Bone fractures




Endometrial proliferative disorders








Hot flushes




Vaginal bleeding




* Significantly less than with letrozole monotherapy.

** Significantly more than with letrozole monotherapy.

Note: Reporting period is during treatment or within 30 days of stopping treatment.

Description of selected adverse reactions

Cardiac adverse reactions

In the adjuvant setting, in addition to the data presented in Table 2, the following adverse events were reported for letrozole and tamoxifen, respectively (at median treatment duration of 60 months plus 30 days): angina requiring surgery (1.0% vs. 1.0%); cardiac failure (1.1% vs. 0.6%); hypertension (5.6% vs. 5.7%); cerebrovascular accident/transient ischaemic attack (2.1% vs. 1.9%).

In the extended adjuvant setting for letrozole (median duration of treatment 5 years) and placebo (median duration of treatment 3 years), respectively: angina requiring surgery (0.8% vs. 0.6%); new or worsening angina (1.4% vs. 1.0%); myocardial infarction (1.0% vs. 0.7%); thromboembolic event* (0.9% vs. 0.3%); stroke/transient ischaemic attack* (1.5% vs. 0.8%) were reported.

Events marked * were statistically significantly different in the two treatment arms.

Skeletal adverse reactions

For skeletal safety data from the adjuvant setting, please refer to Table 2.

In the extended adjuvant setting, significantly more patients treated with letrozole experienced bone fractures or osteoporosis (bone fractures, 10.4% and osteoporosis, 12.2%) than patients in the placebo arm (5.8% and 6.4%, respectively). Median duration of treatment was 5 years for letrozole, compared with 3 years for placebo.

4.9 Overdose

Isolated cases of overdosage with letrozole have been reported.

No specific treatment for overdosage is known. Treatment should be symptomatic and supportive.

5. Pharmacological properties
5.1 Pharmacodynamic properties

Pharmacotherapeutic group: enzyme inhibitors. Non-steroidal aromatase inhibitor (inhibitor of oestrogen biosynthesis); antineoplastic agent.

ATC Code: L02B G04

Pharmacodynamic effects

The elimination of oestrogen-mediated growth stimulation is a prerequisite for tumour response in cases where the growth of tumour tissue depends on the presence of oestrogens and endocrine therapy is used. In postmenopausal women, oestrogens are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens - primary androstenedione and testosterone to oestrone and oestradiol. The suppression of oestrogen biosynthesis in peripheral tissues and the cancer tissue itself can therefore be achieved by specifically inhibiting aromatase enzyme.

Letrozole is a non-steroidal aromatase inhibitor. It inhibits the aromatase enzyme by competitively binding to the haem of the aromatase cytochrome P450, resulting in a reduction of oestrogen biosynthesis in all tissues where present.

In healthy postmenopausal women, single doses of 0.1mg, 0.5mg and 2.5mg letrozole suppresses serum oestrone and oestradiol by 75-78% and 78% from baseline respectively. Maximum suppression is achieved in 48-78 hours.

In postmenopausal patients with advanced breast cancer, daily doses of 0.1 to 5 mg suppress plasma concentration of oestradiol, oestrone, and oestrone sulphate by 75-95% from baseline in all patients treated. With doses of 0.5 mg and higher, many values of oestrone and oestrone sulphate were below the limit of detection in the assays, indicating that higher oestrogene suppression is achieved with these doses. Oestrogen suppression was maintained throughout treatment in all these patients.

Letrozole is highly specific in inhibiting aromatase activity. Impairment of adrenal steroidogenesis has not been observed. No clinically relevant changes were found in the plasma concentrations of cortisol, aldosterone, 11-deoxycortisol, 17- hydroxyprogesterone, and ACTH or in plasma renin activity among postmenopausal patients treated with a daily dose of letrozole 0.1 to 5 mg. The ACTH stimulation test performed after 6 and 12 weeks of treatment with daily doses of 0.1mg, 0.25mg, 0.5mg, 1mg, 2.5mg, and 5 mg did not indicate any attenuation of aldosterone or cortisol production. Thus, glucocorticoid and mineralocorticoid supplementation is not necessary.

No changes were noted in plasma concentrations of androgens (androstenedione and testosterone) among healthy postmenopausal women after 0.1mg, 0.5mg and 2.5 mg single doses of letrozole or in plasma concentrations of androstenedione among postmenopausal patients treated with daily doses of 0.1 to 5 mg, indicating that the blockade of oestrogen biosynthesis does not lead to accumulation of androgenic precursors. Plasma levels of LH and FSH are not affected by letrozole in patients, nor is thyroid function as evaluated by TSH, T4, and T3 uptake test.

Adjuvant treatment

Study BIG 1-98

BIG 1-98 was a multicenter, double-blind study in which over 8000 postmenopausal women with hormone receptor-positive early breast cancer were randomised one of the following treatments: A. tamoxifen for 5 years; B. letrozole for 5 years; C. tamoxifen for 2 years followed by letrozole for 3 years; D. letrozole for 2 years followed by tamoxifen for 3 years.

The primary endpoint was disease free survival (DFS); secondary efficacy endpoints were time to distant metastasis (TDM), distant disease free survival (DDFS), overall survival (OS), systemic disease-free survival (SDFS), invasive contralateral breast cancer and time to breast cancer recurrence.

Efficacy results at a median follow-up of 26 and 60 months

Data in Table 4 reflect results of the Primary Core Analysis (PCA) based on data from the monotherapy arms (A and B) and data from the two switching arms (C and D) at a median treatment duration of 24 months and a median follow-up of 26 months and at a median treatment duration of 32 months and a median follow-up of 60 months.

The 5-year DFS rates were 84% for letrozole and 81.4% for tamoxifen.

Table 4: Primary Core Analysis: Disease-free and overall survival, at a median follow-up of 26 months and at median follow-up of 60 months (ITT population)

Primary Core Analysis

Median follow-up 26 months

Median follow-up 60 months



HR1 (95% CI)



HR1 (95% CI)







Disease-free survival (primary)

- events (protocol definition2)



0.81 (0.70, 0.93)





0.86 (0.77, 0.96) 0.008

Overall survival (secondary)

Number of deaths



0.86 (0.70, 1.06)



0.87 (0.75, 1.01)

HR= Hazard ratio; CI: confidence interval

1 Log rank test, stratified by randomization option and use of chemotherapy(yes/no)

2 DFS events: loco-regional recurrence, distant metastasis, invasive contralateral breast cancer, second (non-breast) primary malignancy, death from any cause without a prior cancer event

Results at a median follow-up of 73 months (monotherapy arms only)

The Monotherapy Arms Analysis (MAA) long-term update of the efficacy of letrozole monotherapy compared to tamoxifen monotherapy (median duration of adjuvant treatment: 5 years) is presented in Table 5.

Table 5: Monotherapy Arms Analysis: Disease-free and overall survival at a median follow-up of 73 months (ITT population)




Hazard Ratio 1


P Value

Disease-free survival events (primary)2



0.88 (0.78, 0.99)


Time to distant metastasis (secondary)



0.85 (0.72, 1.00)


Overall survival (secondary) - deaths



0.87 (0.75, 1.02)


Censored analysis of DFS3



0.85 (0.75, 0.96)

Censored analysis of OS3



0.82 (0.70, 0.96)

1 Log rank test, stratified by randomisation option and use of chemotherapy (yes/no).

2 DFS events: loco-regional recurrence, distant metastasis, invasive contralateral breast cancer, second (non-breast) primary malignancy, death from any cause without a prior cancer event.

3 Observations in the tamoxifen arm censored at the date of selectively switching to letrozole.

Sequential Treatments Analysis (STA)

The Sequential Treatments Analysis (STA) addresses the second primary question of BIG 1-98 namely whether sequencing of tamoxifen and letrozole would be superior to monotherapy. There were no significant differences in DFS, OS, SDFS, or DDFS from switch with respect to monotherapy (Table 6).

Table 6: Sequential treatments analysis of disease-free survival with letrozole as initial endocrine agent (STA switch population)


Number of events1

Hazard ratio2

(97.5% confidence interval)

Cox model P-value

Letrozole → tamoxifen




(0.72, 1.17)





1 Protocol definition, including second non-breast primary malignancies, after switch/beyond two years

2 Adjusted by chemotherapy use

There were no significant differences in DFS, OS, SDFS or DDFS in any of the STA from randomisation pairwise comparisons (Table 7)

Table 7: Sequential Treatments Analyses from randomization (STA-R) of disease-free survival (ITT STA-R population)

Letrozole → tamoxifen


Number of patients



Number of patients with DFS events (protocol definition)



Hazard ratio1 (99% CI)

0.96 (0.76, 1.21)

Letrozole → tamoxifen


Number of patients



Number of patients with DFS events (protocol definition)



Hazard ratio1 (99% CI)

0.87 (0.69, 1.09)

1 Adjusted by chemotherapy use (yes/no)

2 624 (40%) patients selectively crossed to letrozole after tamoxifen arm unblinded in 2005

Study D2407

Study D2407 is an open-label, randomized, multicenter post approval safety study designed to compare the effects of adjuvant treatment with letrozole and tamoxifen on bone mineral density (BMD) and serum lipid profiles. A total of 262 patients were assigned either letrozole for 5 years or tamoxifen for 2 years followed by letrozole for 3 years.

At 24 months, there was a statistically significant difference in the primary endpoint; the lumbar spine BMD (L2 – L4) showed a median decrease of 4.1% for letrozole compared to a median increase of 0.3% for tamoxifen.

No patient with a normal BMD at baseline became osteoporotic during 2 years of treatment and only 1 patient with osteopenia at baseline (T score of -1.9) developed osteoporosis during the treatment period (assessment by central review).

The results for total hip BMD were similar to those for lumbar spine but less pronounced.

There was no significant difference between treatments in the rate of fractures – 15% in the letrozole arm, 17% in the tamoxifen arm.

Median total cholesterol levels in the tamoxifen arm were decreased by 16% after 6 months compared to baseline and this decrease was maintained at subsequent visits up to 24 months. In the letrozole arm, total cholesterol levels were relatively stable over time, giving a statistically significant difference in favour of tamoxifen at each time point.

Extended adjuvant treatment (MA-17)

In a multicentre, double-blind, randomised, placebo-controlled study (MA-17), over 5,100 postmenopausal women with receptor-positive or unknown primary breast cancer, who had completed adjuvant treatment with tamoxifen (4.5 to 6 years) were randomised to either letrozole or placebo for 5 years.

The primary endpoint was disease free survival, defined as the interval between randomisation and the earliest occurrence of loco-regional recurrence, distant metastasis, or contralateral breast cancer.

The first planned interim analysis at a median follow-up of around 28 months (25% of patients being followed up for at least 38 months), showed that letrozole significantly reduced the risk of breast cancer recurrence by 42% compared with placebo (HR 0.58; 95% CI 0.45, 0.76; P = 0.00003). The benefit in favour of letrozole was observed regardless of nodal status. There was no significant difference in overall survival: (letrozole 51 deaths; placebo 62; HR 0.82; 95% CI 0.56, 1.19).

Consequently after the first interim analysis the study was unblinded and continued in an open label fashion and patients in the placebo arm were allowed to switch to letrozole for up to 5 years. Over 60% of eligible patients (disease-free at unblinding) opted to switch to letrozole. The final analysis included 1551 women who switched from placebo to letrozole at a median of 31 months (range 12 to 106 months) after completion of tamoxifen adjuvant therapy. Median duration for letrozole after switch was 40 months.

The final analysis conducted at a median follow-up of 62 months confirmed the significant reduction in the risk of breast cancer recurrence with letrozole.

Table 8 Disease-free and overall survival (Modified ITT population)

Median follow-up 28 months

Median follow-up 62 months





HR (95% CI)2

P value





HR (95% CI)2

P value

Disease-free survival3 Events






(0.45, 0.76)







(0.63, 0.89)

4-year DFS rate





Disease-free survival3, including deaths from any cause







(0.49, 0.78)






(0.77, 1.03)

5-year DFS rate





Distant metastases







(0.44, 0.84)






(0.70, 1.10)

Overall survival







(0.56, 1.19)






(0.95, 1.36)










(0.64, 0.96)

HR = Hazard ratio; CI = Confidence Interval

1 When the study was unblinded in 2003, 1551 patients in the randomized placebo arm (60% of those eligible to switch – i.e. who were disease-free) switched to letrozole at a median 31 months after randomization. The analyses presented here ignore the selective crossover.

2 Stratified by receptor status, nodal status and prior adjuvant chemotherapy.

3 Protocol definition of disease-free survival events: loco-regional recurrence, distant metastasis or contralateral breast cancer.

4 Exploratory analysis, censoring follow-up times at the date of switch (if it occurred) in the placebo arm.

5 Median follow-up 62 months.

6 Median follow-up until switch (if it occurred) 37 months.

In the MA-17 bone substudy in which concomitant calcium and vitamin D were given, greater decreases in BMD compared to baseline occurred with letrozole compared with placebo. The only statistically significant difference occurred at 2 years and was in total hip BMD (letrozole median decrease of 3.8% vs. placebo median decrease of 2.0%).

In the MA-17 lipid substudy there were no significant differences between letrozole and placebo in total cholesterol or in any lipid fraction.

In the updated quality of life substudy there were no significant differences between treatments in physical component summary score or mental component summary score, or in any domain score in the SF-36 scale. In the MENQOL scale, significantly more women in the letrozole arm than in the placebo arm were most bothered (generally in the first year of treatment) by those symptoms deriving from oestrogen deprivation – hot flushes and vaginal dryness. The symptom that bothered most patients in both treatment arms was aching muscles, with a statistically significant difference in favour of placebo.

Neoadjuvant treatment

A double blind trial (P024) was conducted in 337 postmenopausal breast cancer patients randomly allocated either letrozole 2.5 mg for 4 months or tamoxifen for 4 months. At baseline all patients had tumours stage T2-T4c, N0-2, M0, ER and/or PgR positive and none of the patients would have qualified for breast-conserving surgery. Based on clinical assessment there were 55% objective responses in the letrozole arm versus 36% for the tamoxifen arm (P < 0.001). This finding was consistently confirmed by ultrasound (letrozole 35% vs. tamoxifen 25%, P = 0.04) and mammography (letrozole 34% vs. tamoxifen 16%, P < 0.001). In total 45% of patients in the letrozole group vs. 35% of patients in the tamoxifen group (P = 0.02) underwent breast-conserving therapy). During the 4-month pre-operative treatment period, 12% of patients treated with letrozole and 17% of patients treated with tamoxifen had disease progression on clinical assessment.

First-line treatment

One controlled double-blind trial was conducted comparing letrozole 2.5 mg to tamoxifen 20 mg as first-line therapy in postmenopausal women with advanced breast cancer. In 907 women, letrozole was superior to tamoxifen in time to progression (primary endpoint) and in overall objective response, time to treatment failure and clinical benefit.

The results are summarized in Table 9.

Table 9: Results at a median follow-up of 32 months







Time to progression


9.4 months

6.0 months

(95% CI for median)

(8.9, 11.6 months)

(5.4, 6.3 months)

Hazard ratio (HR)


(95% CI for HR)

(0.62, 0.83)



Objective response rate (ORR)


145 (32%)

95 (21%)

(95% CI for rate)

(28, 36%)

(17, 25%)

Odds ratio


(95% CI for odds ratio)

(1.32, 2.40)



Time to progression was significantly longer, and response rate significantly higher for letrozole irrespective of whether adjuvant anti-oestrogen therapy had been given or not. Time to progression was significantly longer for letrozole irrespective of dominant site of disease. Median time to progression was 12.1 months for letrozole and 6.4 months for tamoxifen in patients with soft tissue disease only and median 8.3 months for letrozole and 4.6 months for tamoxifen in patients with visceral metastases.

Study design allowed patients to cross over upon progression to the other therapy or discontinue from the study. Approximately 50% of patients crossed over to the opposite treatment arm and crossover was virtually completed by 36 months. The median time to crossover was 17 months (letrozole to tamoxifen) and 13 months (tamoxifen to letrozole).

Letrozole treatment in the first-line therapy of advanced breast cancer resulted in a median overall survival of 34 months compared with 30 months for tamoxifen (logrank test P=0.53, not significant). The absence of an advantage for letrozole on overall survival could be explained by the crossover design of the study.

Second-line treatment

Two well-controlled clinical trials were conducted comparing two letrozole doses (0.5 mg and 2.5 mg) to megestrol acetate and to aminoglutethimide, respectively, in postmenopausal women with advanced breast cancer previously treated with anti-oestrogens.

Time to progression was not significantly different between letrozole 2.5 mg and megestrol acetate (P=0.07). Statistically significant differences were observed in favour of letrozole 2.5 mg compared to megestrol acetate in overall objective tumour response rate (24% vs 16%, P=0.04), and in time to treatment failure (P=0.04). Overall survival was not significantly different between the 2 arms (P=0.2).

In the second study, the response rate was not significantly different between letrozole 2.5 mg and aminoglutethimide (P=0.06). Letrozole 2.5 mg was statistically superior to aminoglutethimide for time to progression (P=0.008), time to treatment failure (P=0.003) and overall survival (P=0.002).

Male breast cancer

Use of letrozole in men with breast cancer has not been studied.

5.2 Pharmacokinetic properties


Letrozole is rapidly and completely absorbed from the gastrointestinal tract (mean absolute bioavailability: 99.9%). Food slightly decreases the rate of absorption (median tmax 1 hour fasted versus 2 hours fed; and mean Cmax 129 ± 20.3 nmol/litre fasted versus 98.7 ± 18.6 nmol/litre fed) but the extent of absorption (AUC) is not changed. The minor effect on the absorption rate is not considered to be of clinical relevance, and therefore letrozole may be taken without regard to mealtimes.


Plasma protein binding of letrozole is approximately 60%, mainly to albumin (55%). The concentration of letrozole in erythrocytes is about 80% of that in plasma. After administration of 2.5 mg 14C-labelled letrozole, approximately 82% of the radioactivity in plasma was unchanged compound. Systemic exposure to metabolites is therefore low. Letrozole is rapidly and extensively distributed to tissues. Its apparent volume of distribution at steady state is about 1.87 ± 0.47 l/kg.


Metabolic clearance to a pharmacologically inactive carbinol metabolite is the major elimination pathway of letrozole (CLm=2.1 l/h) but is relatively slow when compared to hepatic blood flow (about 90 l/h). The cytochrome P450 isoenzymes 3A4 and 2A6 were found to be capable of converting letrozole to this metabolite. Formation of minor unidentified metabolites and direct renal and faecal excretion play only a minor role in the overall elimination of letrozole. Within 2 weeks after administration of 2.5 mg 14C-labelled letrozole to healthy postmenopausal volunteers, 88.2 ± 7.6% of the radioactivity was recovered in urine and 3.8 ± 0.9% in faeces. At least 75% of the radioactivity recovered in urine up to 216 hours (84.7 ± 7.8% of the dose) was attributed to the glucuronide of the carbinol metabolite, about 9% to two unidentified metabolites, and 6% to unchanged letrozole.

The apparent terminal elimination half-life in plasma is about 2 days. After daily administration of 2.5 mg steady-state levels are reached within 2 to 6 weeks. Plasma concentrations at steady state are approximately 7 times higher than concentrations measured after a single dose of 2.5 mg, while they are 1.5 to 2 times higher than the steady-state values predicated from the concentrations measured after a single dose, indicating a slight non-linearity in the pharmacokinetics of letrozole upon daily administration of 2.5 mg. Since steady-state levels are maintained over time, it can be concluded that no continuous accumulation of letrozole occurs.

Special populations


Age had no effect on the pharmacokinetics of letrozole.

Renal impairment

In a study involving 19 volunteers with varying degrees of renal function (24-hour creatinine clearance 9-116 ml/min) no effect on the pharmacokinetics of letrozole was found after a single dose of 2.5 mg.

Hepatic impairment

In a similar study involving subjects with varying degrees of hepatic function, the mean AUC values of the volunteers with moderate hepatic impairment (Child-Pugh B) was 37% higher than in normal subjects, but still within the range seen in subjects without impaired function. In a study comparing the pharmacokinetics of letrozole after a single oral dose in eight male subjects with liver cirrhosis and severe hepatic impairment (Child-Pugh C) to those in healthy volunteers (N=8), AUC and t1/2 increased by 95 and 187%, respectively. Thus letrozole should be administered with caution to patients with severe hepatic impairment and after consideration of the risk/benefit in the individual patient.

5.3 Preclinical safety data

In a variety of preclinical safety studies conducted in standard animal species, there was no evidence of systemic or target organ toxicity.

Letrozole showed a low degree of acute toxicity in rodents exposed up to 2000 mg/kg. In dogs letrozole caused signs of moderate toxicity at 100 mg/kg.

In repeated-dose toxicity studies in rats and dogs up to 12 months, the main findings observed can be attributed to the pharmacological action of the compound. The no-adverse-effect level was 0.3 mg/kg in both species.

Both in vitro and in vivo investigations on letrozole's mutagenic potential revealed no indications of any genotoxicity.

In a 104-week rat carcinogenicity study, no treatment-related tumours were noted in male rats. In female rats, a reduced incidence of benign and malignant mammary tumours at all the doses of letrozole was found.

Letrozole was embryotoxic and foetotoxic in pregnant rats and rabbits following oral administration at clinically relevant doses. In rats that had live foetuses, there was an increase in the incidence of foetal malformations including domed head and cervical/centrum vertebral fusion. An increased incidence of foetal malformations was not seen in the rabbit. It is not known whether this was an indirect consequence of the pharmacological properties (inhibition of oestrogen biosynthesis) or a direct drug effect (see sections 4.3 and 4.6).

Preclinical observations were confined to those associated with the recognised pharmacological action, which is the only safety concern for human use derived from animal studies.

6. Pharmaceutical particulars
6.1 List of excipients

Tablet core

Lactose monohydrate

Cellulose, microcrystalline (E460)

Maize starch, pregelatinised

Sodium starch glycolate, type A

Magnesium stearate (E572)

Silica, colloidal anhydrous (E551)


Macrogol 8000

Talc (E553b)

Hypromellose (E464)

Titanium dioxide (E171)

Iron oxide yellow (E172)

6.2 Incompatibilities

Not applicable.

6.3 Shelf life

3 years.

6.4 Special precautions for storage

This medicinal product does not require any special storage conditions

6.5 Nature and contents of container

PVC/aluminium blisters.

Pack sizes: 10, 14, 20, 28, 30, 50, 56, 60, 84, 90, 98, 100, 120 tablets per carton box.

Not all pack sizes may be marketed.

6.6 Special precautions for disposal and other handling

No special requirements.

7. Marketing authorisation holder

Winthrop Pharmaceuticals UK Limited

One Onslow Street




United Kingdom

Trading as:

Winthrop Pharmaceuticals

PO Box 611





Trading as: Zentiva, One Onslow Street, Guildford, Surrey, GU1 4YS, UK

8. Marketing authorisation number(s)

PL 17780/0457

9. Date of first authorisation/renewal of the authorisation

4th May 2010

10. Date of revision of the text

12 December 2012