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Breast Cancer Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Stage I, II, IIIA, and Operable IIIC Breast Cancer

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A large, double-blinded, randomized trial (CAN-NCIC-MA17 [NCT00003140]) of 5,187 patients compared the use of letrozole versus placebo in receptor-positive postmenopausal women who received tamoxifen for approximately 5 (4.5–6.0) years.[152] After the first planned interim analysis, when median follow-up for patients on study was 2.4 years, the results were unblinded because of a highly significant (P < .008) difference in DFS (HR, 0.57) favoring the letrozole arm.[152][Level of evidence: 1iDii] After 3 years of follow-up, 4.8% of the women on the letrozole arm had developed recurrent disease or new primaries versus 9.8% on the placebo arm (95% CI for the difference, 2.7%–7.3%). Women on letrozole had significantly more hot flashes, arthritis, arthralgia and myalgia, but less vaginal bleeding. New diagnoses of osteoporosis were more frequent on letrozole (5.8% vs. 4.5%), though the difference was not statistically significant (P = .07). Because of the early unblinding of the study, longer-term comparative data on the risks and benefits of letrozole in this setting will not be available.[153,154] An updated analysis including all events prior to unblinding confirmed the results of the interim analysis.[155] In addition, a statistically significant improvement in distant DFS was found for patients on letrozole (HR, 0.60; 95% CI, 0.43–0.84; P = .002). Although no significant difference was found in the total study population, the node-positive patients on letrozole also experienced a statistically significant improvement in OS (HR, 0.61; 95% CI, 0.38–0.98; P = .04), though the P value was not corrected for multiple comparisons. An ASCO Technology Assessment panel has commented on the implications of these results.[144,145]

Exemestane

A large double-blinded randomized trial (EORTC-10967 [ICCG-96OEXE031-C1396-BIG9702]) of 4,742 patients compared continuing tamoxifen with switching to exemestane for a total of 5 years of therapy in women who had received 2 to 3 years of tamoxifen.[156,157] After the second planned interim analysis, when median follow-up for patients on the study was 30.6 months, the results were released because of a highly significant (P < .005) difference in DFS (HR, 0.68) favoring the exemestane arm.[156][Level of evidence: 1iDii] After a median follow-up of 55.7 months, the HR for DFS was 0.76 (95% CI, 0.66–0.88; P = .001) in favor of exemestane.[158] At 2.5 years after randomization, 3.3% fewer patients on exemestane had developed a DFS event (95% CI, 1.6–4.9). The HR for OS was 0.85 (95% CI, 0.7–1.02; P = .08).[158][Level of evidence: 1iA] Women on exemestane had significantly more arthralgia, diarrhea, hypertension, fractures, arthritis, musculoskeletal pain, carpal tunnel syndrome, insomnia, and osteoporosis, but women on tamoxifen had significantly more gynecologic symptoms, muscle cramps, vaginal bleeding and discharge, thromboembolic disease, endometrial hyperplasia, and uterine polyps. (Refer to the PDQ summary on Gastrointestinal Complications for information on diarrhea and for information on insomnia, refer to the PDQ summary on Sleep Disorders.)

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