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Toxicity of Endocrine Therapy
Source: Breast Cancer Treatment (PDQ®)–Health Professional Version, National Cancer Institute.
Source updated: April 25, 2025 · Captured 2026-09-09.
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Context: Toxicity of Systemic Therapy
Tamoxifen
Long-term follow-up of the ATLAS trial (NCT00003016) included toxicity data. Compared with 5 years, 10 years of tamoxifen therapy increased the risk of the following:[16]
Long-term follow-up of the ATLAS trial (NCT00003016) included toxicity data. Compared with 5 years, 10 years of tamoxifen therapy increased the risk of the following:[16]
Pulmonary embolus: relative risk (RR), 1.87 (95% CI, 1.13–3.07; P = .01).
Long-term follow-up of the ATLAS trial (NCT00003016) included toxicity data. Compared with 5 years, 10 years of tamoxifen therapy increased the risk of the following:[16]
Stroke: RR, 1.06 (95% CI, 0.83–1.36).
Long-term follow-up of the ATLAS trial (NCT00003016) included toxicity data. Compared with 5 years, 10 years of tamoxifen therapy increased the risk of the following:[16]
Ischemic heart disease: RR, 0.76 (95% CI, 0.6–0.95; P = .02).
Long-term follow-up of the ATLAS trial (NCT00003016) included toxicity data. Compared with 5 years, 10 years of tamoxifen therapy increased the risk of the following:[16]
Endometrial cancer: RR, 1.74 (95% CI, 1.30–2.34; P = .0002). Notably, the cumulative risk of endometrial cancer during years 5 to 14 from breast cancer diagnosis was 3.1% for women who received 10 years of tamoxifen versus 1.6% for women who received 5 years of tamoxifen. The mortality rate for years 5 to 14 was 12.2% for women who received 10 years of tamoxifen versus 15% for women who received 5 years of tamoxifen, for an absolute mortality reduction of 2.8%.
Aromatase Inhibitors
Patients on tamoxifen more frequently developed endometrial cancer and cerebrovascular accidents, whereas patients on anastrozole had more fracture episodes. The frequency of myocardial infarction was similar in both groups. Except for a continued increased frequency of endometrial cancer in the tamoxifen group, these differences did not persist in the posttreatment period.[17]
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