Letrozole in the treatment of breast cancer

Endocrine therapy, predominantly using the antioestrogen tamoxifen, has long been a key treatment strategy for oestrogen receptor-positive breast cancer. An alternative approach is to treat patients with aromatase inhibitors, which suppress oestrogen biosynthesis. Letrozole, and other third-generation aromatase inhibitors, are highly specific and potent inhibitors of oestrogen production, which markedly reduce circulating oestrogen levels and whole-body aromatisation of androgen precursors after menopause. In postmenopausal women with hormone receptor-positive or receptor-unknown breast cancer, letrozole has been shown to be superior to megestrol acetate and aminoglutethimide in second-line treatment for advanced breast cancer. Letrozole was also superior to tamoxifen in first-line treatment for advanced breast cancer, as well as in systemic preoperative (neoadjuvant) treatment of locally advanced breast cancer. A recent adjuvant trial demonstrated significant superiority of letrozole over tamoxifen in disease-free survival, and another trial demonstrated that treatment for early breast cancer with letrozole, following 5 years of adjuvant tamoxifen (extended adjuvant therapy), significantly improved disease-free survival compared with placebo, irrespective of nodal status. Ongoing trials will determine whether the optimal use of letrozole in the adjuvant therapy of early breast cancer is as a replacement for tamoxifen, or sequenced additionally before or after tamoxifen.     

Letrozole in the treatment of breast cancer

Endocrine therapy, predominantly using the antioestrogen tamoxifen, has long been a key treatment strategy for oestrogen receptor-positive breast cancer. An alternative approach is to treat patients with aromatase inhibitors, which suppress oestrogen biosynthesis. Letrozole, and other third-generation aromatase inhibitors, are highly specific and potent inhibitors of oestrogen production, which markedly reduce circulating oestrogen levels and whole-body aromatisation of androgen precursors after menopause. In postmenopausal women with hormone receptor-positive or receptor-unknown breast cancer, letrozole has been shown to be superior to megestrol acetate and aminoglutethimide in second-line treatment for advanced breast cancer. Letrozole was also superior to tamoxifen in first-line treatment for advanced breast cancer, as well as in systemic preoperative (neoadjuvant) treatment of locally advanced breast cancer. A recent adjuvant trial demonstrated significant superiority of letrozole over tamoxifen in disease-free survival, and another trial demonstrated that treatment for early breast cancer with letrozole, following 5 years of adjuvant tamoxifen (extended adjuvant therapy), significantly improved disease-free survival compared with placebo, irrespective of nodal status. Ongoing trials will determine whether the optimal use of letrozole in the adjuvant therapy of early breast cancer is as a replacement for tamoxifen, or sequenced additionally before or after tamoxifen.     

Letrozole in the treatment of breast cancer

Over the last 30 years the role of tamoxifen in breast cancer treatment has been progressively expanded by clinical investigation to encompass the entire spectrum of disease from cancer chemoprevention to palliation of advanced disease. The primacy of tamoxifen for these indications in postmenopausal women is now under challenge by the selective aromatase inhibitors, a class of endocrine agent that induces oestrogen deprivation rather than oestrogen receptor blockade. This review considers the biochemical, pharmacological and clinical properties of the nonsteroidal aromatase inhibitor letrozole. This agent is superior to tamoxifen for the treatment of metastatic breast cancer, a finding that suggests that letrozole may ultimately eclipse tamoxifen for other indications, including chemoprevention. Further clinical investigation will be necessary to establish the risks and benefits of letrozole versus tamoxifen for each new indication, with adjuvant therapy being the next in line. The object of this review is to provide a reference source on the biochemical, pharmacological and clinical properties of letrozole for clinicians to consider both established and future indications.     

Letrozole: present and future role in the treatment of breast cancer

State of the art hormonal therapy for women with breast cancer has evolved over the last few years. Tamoxifen used to be the gold standard for adjuvant treatment of postmenopausal women with hormone-sensitive early breast cancer and also for patients with metastatic disease in whom hormonal manipulation was considered, but the introduction of third generation aromatase inhibitors has changed this concept. This article discusses the clinical implications of recent trials with one of the aromatase inhibitors letrozole, including pharmacokinetic and pharmacodynamic data as well as recent data on relative benefits and side effects compared with other available hormonal agents. Relevant ongoing clinical-translational trials evaluating this agent are also discussed.     

来曲唑与紫杉醇联合顺铂治疗转移性乳腺癌的疗效观察

目的 观察来曲唑与紫杉醇联合顺铂治疗转移性乳腺癌的疗效及不良反应.方法 我院62例转移性乳腺癌患者随机分成2组.观察组31例,采用来曲唑与紫杉醇联合顺铂治疗;对照组31例,以紫杉醇化疗为主,加来曲唑进行内分泌治疗.观察两组患者预后及不良反应发生情况.结果 采用来曲唑与紫杉醇联合顺铂治疗组患者缓解率及生存率明显高于对照组,且不良反应较少,与对照组比较差异有统计学意义（P〈0.05）.结论 来曲唑与紫杉醇联合顺铂治疗转移性乳腺癌效果显著,不良反应较少.     

Letrozole : in postmenopausal hormone-responsive early-stage breast cancer

Letrozole is a highly selective, nonsteroidal, third-generation aromatase inhibitor approved for first-line and extended adjuvant therapy in postmenopausal women with hormone-responsive, early-stage breast cancer. Binding of letrozole to the haeme component of the cytochrome P450 subunit of aromatase inhibits estrogen biosynthesis throughout the body. As first-line adjuvant therapy in approximate, equals 8000 postmenopausal women with hormone-responsive, early-stage breast cancer, once-daily letrozole 2.5mg significantly prolonged disease-free survival (DFS; primary endpoint) and reduced the risk of relapse at distant sites relative to once-daily tamoxifen 20mg in the ongoing Breast International Group 1-98, double-blind, multinational trial. The median duration of follow-up for this primary core analysis was 25.8 months. Extended adjuvant therapy with once-daily letrozole 2.5mg significantly prolonged DFS relative to placebo treatment at a median follow-up of 30 months (primary endpoint) in the MA-17 trial in approximate, equals 5000 postmenopausal women who were disease free after 4.5-6 years of tamoxifen therapy for hormone-responsive, early-stage breast cancer. Letrozole treatment for up to 5 years was generally well tolerated in this clinical setting. As first-line treatment, relative to tamoxifen, letrozole was associated with a significantly lower incidence of venous thromboembolitic events, vaginal bleeding, hot flushes and night sweating, whereas the incidence of cardiac failure, bone fractures and arthralgia was higher in letrozole recipients.     

Letrozole: a review of its use in postmenopausal women with breast cancer

Letrozole (Femara), a nonsteroidal, third-generation aromatase inhibitor administered orally once daily, has shown efficacy in the treatment of postmenopausal women with early-stage or advanced, hormone-sensitive breast cancer. In early-stage disease, extending adjuvant endocrine therapy with letrozole (beyond the standard 5-year period of tamoxifen) improved disease-free survival; compared with placebo there was a 43% relative reduction in disease recurrences or new contralateral breast tumours at a median follow-up of 2.4 years. The results of 4 months' neoadjuvant treatment with letrozole or tamoxifen in postmenopausal women with untreated primary disease favour letrozole. In advanced breast cancer, letrozole was superior to tamoxifen as first-line treatment; time to disease progression was significantly longer (9.4 vs 6.0 months, p < 0.0001) and objective response rate was significantly greater with letrozole, but median overall survival was similar between groups. For second-line therapy of advanced breast cancer that had progressed on antiestrogen therapy, letrozole showed efficacy equivalent to that of anastrozole and similar to or better than that of megestrol acetate. Letrozole is generally well tolerated and has a similar tolerability profile to tamoxifen; the most common treatment-related adverse events were hot flushes, nausea and hair thinning. In patients with tumours that had progressed on antiestrogen therapy, letrozole was tolerated as least as well as, or better than, anastrozole or megestrol acetate. In the trial of extended adjuvant therapy, adverse events reported more frequently with letrozole than placebo were hot flushes, arthralgia, myalgia and arthritis. The long-term effects of letrozole on bone mineral density or lipid profile have not been determined and these parameters may require monitoring. In several pharmacoeconomic modelling studies from various public healthcare system perspectives, letrozole was considered a cost effective choice for first-line (vs tamoxifen) or second-line (vs megestrol acetate) treatment for advanced breast cancer in postmenopausal women. In conclusion, letrozole 2.5 mg/day is effective in the treatment of postmenopausal women with early-stage or advanced breast cancer. The efficacy, cost effectiveness and favourable tolerability profile of letrozole are reflected in current treatment guidelines recommending the drug as first-line therapy for advanced breast cancer. Letrozole is superior to tamoxifen for first-line treatment and is at least as effective as standard second-line treatments in disease that has progressed on antiestrogen therapy. For early-stage disease, letrozole is superior to tamoxifen in the neoadjuvant setting, and prolongs disease-free survival when administered after the standard 5-year period of adjuvant tamoxifen therapy.     

国产来曲唑片应用于乳腺癌内分泌治疗的 生物等效性研究

目的：研究国产来曲唑片在人体内的生物利用度,并与参比制剂比较,评价其生物等效性。方法20名健康男性志愿者随机口服国产来曲唑片2.5 mg（受试制剂）或进口来曲唑片2.5 mg（参比制剂）后,采用高效液相色谱法测定不同时刻血浆中来曲唑的浓度,用WinNonlin5.2.1数据统计软件计算药代动力学参数,并评价其生物等效性。结果单次口服国产来曲唑片2.5 mg或参比制剂2.5 mg后,药代动力学参数分别为：受试制剂的t1/2：（43.91±12.68）h、Cmax：（30.94±7.05）ng·mL^-1、Tmax：（2.13±2.59）h、AUC0-t：（1478±421）ng·h·mL^-1;参比制剂的t1/2：（40.49±12.23）h、Cmax：（27.93±5.41）ng mL^-1、Tmax：（2.20±1.72）h、AUC0-t：1503±396 ng·h·mL^-1。经方差分析、双单侧t检验和[1-2α]％置信区间法进行生物等效性评价,其中Tmax采用非参数检验法,结果表明受试制剂与参比制剂间的各药动学参数的差异无统计学意义（P〉0.05）。结论国产来曲唑片与进口来曲唑片在人体内具有生物等效性。     

Letrozole: a pharmacoeconomic review of its use in postmenopausal women with breast cancer

Letrozole (Femara), an aromatase inhibitor that blocks estrogen synthesis by inhibiting the final step of the estrogen biosynthetic pathway, is approved for use in a wide range of breast cancer settings. Randomised clinical trials in postmenopausal women with hormone-responsive early-stage breast cancer have demonstrated that, as adjuvant therapy, letrozole has greater efficacy than tamoxifen. It is also more effective than placebo as extended adjuvant therapy after completion of tamoxifen therapy in these patients. In women with hormone-responsive advanced breast cancer, letrozole is superior to tamoxifen in prolonging the time to disease progression and time to treatment failure in a first-line setting, and is at least as effective as anastrozole and more effective than megestrol for some endpoints (in one of two trials) in a second-line setting. Letrozole is generally well tolerated, and in a health-related quality-of-life analysis from a large clinical trial, patient well-being with letrozole as extended adjuvant therapy did not differ from that with placebo. Modelled analyses from the UK and the US suggest that, in postmenopausal women with hormone-receptor-positive early-stage breast cancer, letrozole is likely to be a cost-effective alternative to tamoxifen as adjuvant therapy; moreover, using letrozole as extended adjuvant therapy after tamoxifen, rather than no further treatment, is also a cost-effective treatment strategy. Sensitivity analyses have shown these results to be robust. In terms of direct healthcare costs, pharmacoeconomic models suggest that letrozole is a cost-effective alternative to tamoxifen as first-line therapy in postmenopausal women with hormone-responsive advanced breast cancer from the perspectives of the UK NHS, the Canadian and Italian public healthcare systems and the Japanese national health insurance system. Incremental costs per QALY or progression-free year gained over tamoxifen were well within the recommended limits for acceptability of new agents that are more effective and more expensive than existing therapies in the UK, Japan and Canada. Modelled analyses from the UK and Canada have also suggested that letrozole is cost effective as second-line therapy for advanced breast cancer in postmenopausal women who have disease progression following anti-estrogen therapy. In conclusion, letrozole is an effective and well tolerated treatment for postmenopausal women with early-stage or advanced hormone-responsive breast cancer. Pharmacoeconomic analyses from UK and North American perspectives support the use of letrozole in hormone-responsive early-stage breast cancer in both the adjuvant and extended adjuvant settings. In addition, other modelled analyses conducted in a variety of healthcare systems across different countries consistently suggest that letrozole is cost effective in advanced treatment settings.     

Non-steroidal anti-estrogens in the treatment of breast cancer

The non-steroidal selective estrogen receptor modulator (SERM) tamoxifen has been used as standard first-line therapy for postmenopausal breast cancer since the 1970s, during which time over 400,000 lives have been saved. Nevertheless, much attention has been paid to the side effect profile of tamoxifen, particularly in terms of cardiovascular and endometrial abnormalities. Third generation non-steroidal aromatase inhibitors, such as anastrozole and letrozole, have been approved as an alternative, although it is still too early to judge what long-term adverse effects might be associated with prolonged restriction of the supply of estrogen. Novel SERMs have demonstrated improved characteristics over tamoxifen, reducing or eliminating certain adverse events while retaining breast tumor-reducing efficacy. Thus, these agents could provide a direct substitute for tamoxifen. In addition, other estrogen receptor (ER) subtype-selective modulators are under investigation, and the importance of ERbeta as a positive prognostic indicator may open up further therapeutic opportunities. Resistance to hormonal therapies is still a major problem and identifiying the onset of the development of resistance, together with earlier intervention with inhibitors of growth-factor driven cell survival pathways, in combination or sequentially, requires more intense study.     

Current standards in the treatment of breast cancer

Breast cancer is the most frequent malignoma in female individuals: more than 10 out 100 females suffer from the disease. The understanding of breast cancer as a primarily local disease has undergone a fundamental change in the last few decades. While throughout most of the previous century breast cancer was still mainly conceived of as a predominantly local disease, the radical nature of surgery can now be reduced to a minimum by the use of breast conserving procedures and axillary sentinel lymph node excision. The systemic use of cytostatic and endocrine therapeutic modalities has simultaneously provided a major overall survival benefit for patients treated in accordance with current therapeutic standards. The multidisciplinary treatment challenge of breast cancer comprises nowadays surgery, systemic treatment and radiotherapy and aims to a more individualized therapy.     

芳香酶抑制剂治疗乳腺癌的研究进展

芳香酶抑制剂通过阻断绝经后妇女内源性雌激素的合成,降低体内循环雌激素水平,达到有效阻滞乳腺癌生长,甚至导致癌细胞死亡的效应。第三代芳香酶抑制剂来曲唑(letrozole)、阿那曲唑(anastrozole)、vorozole(非甾体型,Ⅱ型)和伊西美坦(exemestane)(甾体型．I型)．用于二线治疗绝经后雌激素受体阳性的乳腺癌Ⅲ期临床试验结果表明,与常规治疗相比具有明显的优越性。最近．一线治疗转移性乳腺癌的初步试验结果表明,芳香酶抑制剂有可能取代他莫昔芬(tamoxifen)作为一线治疗药物。新一代芳香酶抑制剂的选择性高．耐受性好．目前在临床上得到广泛的应用。本主要对芳香酶抑制剂的研究进展、药理作用机理、临床应用和可能的应用前景等做一综述。     

Abemaciclib for the treatment of breast cancer

Introduction: There have been numerous clinical trials of CDK4/6 inhibitors performed on various carcinomas including breast cancer. One such inhibitor tested and which has ongoing clinical trials for breast cancer is abemaciclib. Abemaciclib is a molecular-targeted agent that targets basic cell cycle regulatory mechanisms.

Areas covered: This review discusses the available clinical data and ongoing clinical trials of abemaciclib in breast cancer.

Expert opinion: Abemaciclib has demonstrated a clear anti-tumour effect and manageable toxicity against HR-positive, HER2-negative breast cancer in many clinical trials and is expected to be an important standard therapy. However, currently, besides oestrogen receptor expression, there is a definite lack of predictive biomarkers for response and/or tolerance to abemaciclib, which is important for patient selection. Another problem is that its contribution to overall survival (OS) has not been shown. And while two large the phase 3 study highlighted the anti-tumour effect of abemaciclib, the OS results are awaited. Furthermore, the effect on brain metastases is expected to be unique to abemaciclib as the response of brain metastasis in HR-positive breast cancer patients has been confirmed in a few cases with case collection still ongoing.     

Entinostat for the treatment of breast cancer

Introduction: Breast cancer accounts for 29% of malignant tumors. It is an heterogenous disease covering a spectrum of different molecular subtypes. Epigenetic aberrations may affect gene expression through DNA and histone proteins modifications thus promoting tumor progression and resistance to anti- tumor treatment.

Area covered: This article explores the potential role of entinostat in the treatment of breast cancer. The clinical trials evaluating entinostat are discussed, highlighting preclinical data and early-phase clinical studies results. The emerging activity of entinostat in several clinical settings is evaluated by focusing on endocrine-resistant, HER2 positive and triple-negative breast cancer with promising activity in boosting the immune-system.

Expert opinion: Entinostat, a synthetic benzamide derivative class I histone deacetylases (HDACs) inhibitor, inhibits cell proliferation and promotes apoptosis in breast cancer. Several results from clinical trials demonstrate that the addition of an epigenetic therapy to antiestrogen therapy may be an effective approach to targeting resistance pathways in breast cancer, particularly in hormone-positive disease. Agents such as entinostat may have a role in immunogenic modulation. Genetic and pharmacological inhibition studies identified HDAC as a key determinant in the reversal of carcinoma immune escape. This offers the rationale for combining HDAC inhibitors with immunotherapy, including therapeutic cancer vaccines.     

Olaparib for the treatment of breast cancer

Introduction: Basal-like breast cancer is characterized by being triple negative and aggressive. Defects in DNA repair is a promising therapeutic target as BRCA alterations are found in 11 to 42% of these tumors, with a frequency varying according to family history and ethnicity. The oral PARP inhibitors exploit this deficiency through a synthetic lethality and are considered as promising anticancer therapies, especially in patients harboring BRCA1 or BRCA 2 mutations.

Areas covered: Olaparib is one of the most widely investigated PARP inhibitors. Here, the preclinical data, completed clinical trials and ongoing investigations are discussed.

Expert opinion: PARP inhibitors show promising results in breast cancer. However, several issues are raised including the identification of biomarkers to predict treatment response and strategies to counteract emerging resistance. Moreover, the results from ongoing phase III trials of olaparib in breast cancer are still awaited.     

Vinflunine for the treatment of breast cancer

Introduction: Breast cancer is the most frequently diagnosed cancer and the highest cause of cancer mortality in females worldwide. The development of drugs improving overall survival in late-stage metastatic breast cancer remains a challenge.

Vinflunine is the most recently developed drug in the vinca alkaloid class. Its arrival has been eagerly awaited for treatment of solid tumors, and in particular, for metastatic breast cancer.

Areas covered: The pharmacological features of vinflunine are described. Its clinical development as monotherapy or in combination in metastatic breast cancer is detailed. A literature search on the topic was conducted through PubMed, clinical trials and the proceedings of the main cancer congresses.

Expert opinion: The overall results from phase III studies, and in particular those that combined vinflunine with capecitabine, have been less favorable. The combination’s effectiveness was at best moderate compared with other drugs which also target metastatic breast cancer, and complicated by significant hematological and gastrointestinal adverse effects. Its use in advanced metastatic breast cancer cannot currently be recommended.     

Neratinib for the treatment of breast cancer

Introduction: Neratinib is an orally available, pan-HER inhibitor with clinical activity in patients with HER2-amplified and HER2-mutated breast cancer.

Areas covered: A summary of publically available and relevant clinical data on neratinib.

Expert opinion: Neratinib (N) is clearly distinct from lapatinib (L), a difference based on its broad anti-HER effect, its covalent target binding and its toxicity profile. The main toxicity of neratinib is gastro-intestinal and is essentially limited to diarrhea. Although not directly compared with single agent lapatinib, skin toxicity is much less pronounced with N. The direct clinical comparison of N-capecitabine versus L-capecitabine is the subject of the ongoing NALA-trial. In patients with advanced disease, neratinib has clinically relevant activity in patients with trastuzumab(T)-pretreated and unpretreated disease. In patients having completed one year of adjuvant trastuzumab, an additional year of neratinib further reduces the risk of recurrence of invasive disease. The activity of neratinib in HER2-mutated advanced disease is subject of ongoing clinical trials but preclinical and early clinical results are promising. Neratinib is a usefull drug and a valuable addition to the different anti-HER2-drugs avalaible for patients with HER2-overexpressing and HER2-mutated breast cancer.     

Pazopanib for the treatment of breast cancer

INTRODUCTION: Several clinical trials have shown clinical benefit of angiogenesis inhibitors in the treatment of solid tumors. Pazopanib is a multitargeted tyrosine kinase inhibitor that is currently approved for the treatment of patients with advanced renal cell carcinoma (RCC). AREAS COVERED: In this article, the clinical development of pazopanib as it relates to breast cancer is reviewed including its evaluation in clinical trials and side effect profile. Preclinical data show the anti-tumor activity of pazopanib in animal models. Several trials of pazopanib monotherapy and combination therapy in breast cancer have been completed or are underway. EXPERT OPINION: The development of biomarkers predictive of response and toxicity to angiogenesis inhibitors remains a challenging endeavor and is necessary to help guide treatment decision.