Letrozole versus Tamoxifen as First-Line Treatment for Metastatic Breast Cancer
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Background: Randomized trials in postmenopausal women have shown a benefit to substituting aromatase inhibitors for tamoxifen or using them sequentially following a full course of tamoxifen. The aromatase inhibitor letrozole has also been utilized for ovarian induction in premenopausal women. Case Report: A premenopausal woman with early stage breast cancer became amenorrheic with adjuvant chemotherapy, and remained so during 5 years of daily tamoxifen. After discontinuing tamoxifen, laboratory studies confirmed an apparent postmenopausal state. Menses resumed following a 2-week course of letrozole. Conclusion: Aromatase inhibitors need to be used with caution in women who stop menstruating following adjuvant chemotherapy or tamoxifen.
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Purpose Previous analyses of adjuvant studies of aromatase inhibitors versus tamoxifen, including the Breast International Group (BIG) 1-98 study, have suggested a small numerical excess of cardiac adverse events (AEs) on aromatase inhibitors, a reduction in the incidence of hypercholesterolemia on tamoxifen, and significantly higher incidence of thromboembolic AEs on tamoxifen. The purpose of the present study is to provide detailed updated information on these AEs in BIG 1-98. Patients and Methods Eight thousand twenty-eight postmenopausal women with receptor-positive early breast cancer were randomly assigned (double-blind) between March 1998 and May 2003 to receive 5 years of adjuvant endocrine therapy with letrozole, tamoxifen, or a sequence of these agents. Seven thousand nine hundred sixty-three patients who actually received therapy are included in this safety analysis, which focuses on cardiovascular events. AE recording ceased 30 days after therapy completion (or after switch on the sequential arms). Results Baseline comorbidities were balanced. At a median follow-up time of 30.1 months, we observed similar overall incidence of cardiac AEs (letrozole, 4.8%; tamoxifen, 4.7%), more grade 3 to 5 cardiac AEs on letrozole (letrozole, 2.4%; tamoxifen, 1.4%; P = .001)—an excess only partially attributable to prior hypercholesterolemia—and more overall (tamoxifen, 3.9%; letrozole, 1.7%; P < .001) and grade 3 to 5 thromboembolic AEs on tamoxifen (tamoxifen, 2.3%; letrozole, 0.9%; P < .001). There was no significant difference between tamoxifen and letrozole in incidence of hypertension or cerebrovascular events. Conclusion The present safety analysis, limited to cardiovascular AEs in BIG 1-98, documents a low overall incidence of cardiovascular AEs, which differed between treatment arms.
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Recent investigations of novel aromatase inhibitors have addressed several important questions related to the biochemical effects of this class of drugs. While aromatase inhibitors such as aminoglutethimide, formestane (given by the oral and i.m. route), rogletimide and fadrozole administered at different doses have been found to inhibit in vivo aromatization by 60–93%, the novel aromatase inhibitors, letrozole and anastrozole, are shown to inhibit in vivo aromatization by about 98%. Contrary to previous studies on aromatase inhibitors reporting plasma oestrogens sustained at 30–50% of their control levels letrozole and anastrozole suppress plasma oestrone sulphate by approximately 95%. Future studies should explore cross-resistance of aromatase inhibitors and steroidal antioestrogens and between different types of aromatase inhibitors. A major goal is to evaluate alterations in tissue oestrogen concentration as well as growth factor expression in response to oestrogen deprivation with aromatase inhibitors.
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The aromatase inhibitor letrozole, as compared with tamoxifen, improves disease-free survival among postmenopausal women with receptor-positive early breast cancer. It is unknown whether sequential treatment with tamoxifen and letrozole is superior to letrozole therapy alone.In this randomized, phase 3, double-blind trial of the treatment of hormone-receptor-positive breast cancer in postmenopausal women, we randomly assigned women to receive 5 years of tamoxifen monotherapy, 5 years of letrozole monotherapy, or 2 years of treatment with one agent followed by 3 years of treatment with the other. We compared the sequential treatments with letrozole monotherapy among 6182 women and also report a protocol-specified updated analysis of letrozole versus tamoxifen monotherapy in 4922 women.At a median follow-up of 71 months after randomization, disease-free survival was not significantly improved with either sequential treatment as compared with letrozole alone (hazard ratio for tamoxifen followed by letrozole, 1.05; 99% confidence interval [CI], 0.84 to 1.32; hazard ratio for letrozole followed by tamoxifen, 0.96; 99% CI, 0.76 to 1.21). There were more early relapses among women who were assigned to tamoxifen followed by letrozole than among those who were assigned to letrozole alone. The updated analysis of monotherapy showed that there was a nonsignificant difference in overall survival between women assigned to treatment with letrozole and those assigned to treatment with tamoxifen (hazard ratio for letrozole, 0.87; 95% CI, 0.75 to 1.02; P=0.08). The rate of adverse events was as expected on the basis of previous reports of letrozole and tamoxifen therapy.Among postmenopausal women with endocrine-responsive breast cancer, sequential treatment with letrozole and tamoxifen, as compared with letrozole monotherapy, did not improve disease-free survival. The difference in overall survival with letrozole monotherapy and tamoxifen monotherapy was not statistically significant. (ClinicalTrials.gov number, NCT00004205.)
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Background: The antiestrogen tamoxifen has potent activity against estrogen receptor–positive breast cancer, but two nonsteroidal aromatase inhibitors, letrozole and anastrozole, show considerable advantages over tamoxifen with respect to patient survival and tolerability. To determine the optimal way to use letrozole and tamoxifen, we studied their effects on a breast tumor xenograft model, MCF-7Ca, that is responsive to both antiestrogens and aromatase inhibitors. Methods: Female ovariectomized BALB/c athymic nude mice carrying xenograft tumors were treated daily subcutaneously with one of the following first-line therapies for varying durations: no drug (control), tamoxifen (100 μg/day) alone, letrozole (10 μg/day) alone, both drugs at the same time, or alternating 4-week courses of each drug (beginning with a course of tamoxifen or beginning with a course of letrozole). Tumor volumes and weights were estimated using linear mixed-effects models. The time to tumor doubling was calculated, and tumor weights in the treatment groups were compared, with adjustments for multiple comparisons being made with either Tukey's or Dunnett's procedure. Second-line therapies (with tamoxifen, letrozole, or fulvestrant) were initiated when tumors doubled in size under first-line therapies. All statistical tests were two-sided. Results: The times for doubling of tumor volume were as follows: control, 3–4 weeks; tamoxifen alone, 16 weeks; tamoxifen alternating with letrozole, 17–18 weeks; tamoxifen plus letrozole, 18 weeks; letrozole alternating with tamoxifen, 22 weeks; letrozole alone, 34 weeks. First-line treatment with letrozole was superior to treatment with tamoxifen alone or with the two drugs combined (at week 16, both P<.001). Alternating tamoxifen and letrozole and alternating letrozole and tamoxifen were also not as effective as letrozole alone (at week 16, P = .002 and P<.001, respectively). Tumors progressing on tamoxifen remained sensitive to second-line therapy with letrozole compared with those remaining on tamoxifen at the end of treatment (week 28, P<.001), whereas tumors progressing on letrozole were unaffected by second-line treatment with the antiestrogens tamoxifen or fulvestrant. Conclusions: First-line letrozole therapy extends time for tumor progression in this model relative to the other treatment regimens tested. However, further studies are needed to determine the most effective second-line therapy for tumors that progress on letrozole.
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Tamoxifen has been the mainstay of breast cancer therapy. Over time, resistance to tamoxifen may develop. The aromatase inhibitors have proven to be a powerful drug for use in hormone-sensitive early breast cancer. The switching strategy was designed to combine the apparent superior efficacy of aromatase inhibitors with tamoxifen favourable effects.This study was performed on 120 postmenopausal women with histologically confirmed, hormone receptor-positive, operable invasive breast carcinoma who remained free of disease after 2 years of adjuvant tamoxifen therapy. They were randomized to receive either letrozole 2.5mg/day (60 patients) or to continue 20mg/day tamoxifen for 5 years (60 patients).The treatment groups were well balanced in terms of age, tumor size, nodal status, oestrogen and progesterone receptor status, and previous surgery. The disease recurred in 10 patients in the group receiving tamoxifen and 3 patients in the same group switched to letrozole. There were 8 deaths in the group receiving tamoxifen and 3 deaths in the group of patients who switched to letrozole. Disease-free survival was higher in the group of patients who switched to letrozole compared to the group of patients who received tamoxifen (p=0.04), while the overall survival was not statistically significantly different in the two groups. Letrozole was associated with a significantly lower rate of vaginal bleeding and thromboembolic events. However, bone fractures and adverse cardiovascular events were more frequent in the arm receiving letrozole than in the arm receiving tamoxifen but these differences were not statistically significant.Switching to letrozole after 2 years of tamoxifen may be better than continuing five years of tamoxifen therapy as regard efficacy and tolerability. Further study is recomended on a larger group of patients to verify this finding.Breast cancer - Hormonal treatment - Letrozole - Tamoxifen.
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