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Treatment-related toxicities may explain lack of overall survival benefit with aromatase inhibitors

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Aromatase inhibitors used as up-front therapy among postmenopausal women with breast cancer are associated with improvements in disease-free survival but not overall survival. Recent data published in the Journal of the National Cancer Institute demonstrates that drug-related toxicities, such as cardiovascular disease and bone fractures, may explain the lack of overall survival benefit compared with tamoxifen.

“We urge clinicians to consider carefully the toxicity profiles of different endocrine therapy options for breast cancer and choose those that best suit their patients’ baseline health characteristics,” the researchers wrote. “Investigators participating in practice-changing clinical trials or in trial overviews should rigorously report not only efficacy data but also data on less common and potentially serious toxicities.”

The meta-analysis, conducted by researchers from Canada, Slovenia and Spain, included seven randomized controlled trials with data for 30,023 patients. The studies compared aromatase inhibitors with tamoxifen as primary endocrine therapy in postmenopausal women. The researchers used ORs, 95% CIs, absolute risks and the number needed to harm associated with one adverse event to compute for prespecified serious adverse events, including cardiovascular disease, cerebrovascular disease, bone fractures, thromboembolic events, endometrial carcinoma and other second cancers, not including new breast cancer, according to the study.

Compared with tamoxifen, longer duration of aromatase inhibitor therapy was associated with an increased risk for cardiovascular disease (OR=1.26; 95% CI, 1.10-1.43) and bone fractures (OR=1.47; 95% CI, 1.34-1.61). However, treatment was associated with a decreased risk for venous thrombosis (OR=0.55; 95% CI, 0.46-0.64) and endometrial carcinoma (OR=0.34; 95% CI, 0.22-0.53).

There was a non-statistically significant increased risk for death without recurrence after 5 years of aromatase inhibitor therapy vs. 5 years of tamoxifen alone or tamoxifen for 2 to 3 years followed by aromatase inhibitor therapy for 2 to 3 years (OR=1.11; 95% CI, 0.98-1.26).

According to the authors of an accompanying editorial, data from the current meta-analysis, and others similar to it, are not mature due to the short follow-up length of trials of adjuvant aromatase inhibitors in this patient population. Therefore, they wrote, “A practical approach while we await further maturation of adjuvant endocrine data would be to choose initial endocrine therapy for the individual patient with careful attention to the risk of breast cancer recurrence, the risk of toxicity and comorbidities.”

Ultimately, they wrote, these results, coupled with those of another recent meta-analysis, suggest that switching strategies is rational and effective. They conclude, “We should not ‘ditch the switch.’”

For more information:

• Amir E. J Natl Cancer Inst. 2011;doi:10.1093/jnci/djr242.
• Puhalla S. J Natl Cancer Inst. 2011;doi:10.1093/jnci/djr302.

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