Improving Endocrine Treatment Decisions in ER+ Breast Cancer

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The Breast Cancer Index (BCI) helps determine whether an additional five years of anti-estrogen therapy is warranted for patients with early-stage, ER-positive breast cancer. This tool is helpful for determining the appropriateness of extended endocrine therapy, says Denise A. Yardley, MD, who has used the assay in her practice for selected patients.

Extended hormonal therapy offers the greatest benefit to individuals at higher risk, says Debu Tripathy, MD. At this time, BCI is the only assay that has been tested specifically in an extended randomized hormonal study, giving it the greatest promise, adds Tripathy. Extended hormonal therapy increases the likelihood of an adverse event, including the development of uterine cancer. Additional toxicity data will be available as clinical trials evaluating extended aromatase inhibition mature, states Tripathy.

Other tests are available for patients with breast cancer, including Oncotype DX. This assay is useful for patients with HER2-negative disease but did not help predict outcomes for those with HER2-positive breast cancer, says Edith Perez, MD. There is a growing interest in investigating whole genome assays to offer predictability in this setting; however, at this time, many of these markers have not panned out, adds Perez.

Findings from the phase III SOFT trial also shed light on improving care with tamoxifen. In this study, patients were randomized to 5 years of tamoxifen (n = 1018) or ovarian function suppression (OFS) added to either tamoxifen (n = 1015) or exemestane (n = 1014). At a median follow-up of 5.6 years, the addition of OFS to tamoxifen resulted in a small but not significant improvement in disease-free survival (DFS; 86.6% vs 84.7%; HR = .83; P = .10).

A subset analysis from the SOFT trial showed an advantage to individuals who received OFS plus tamoxifen or an aromatase inhibitor versus tamoxifen, says Perez. In patients who remained premenopausal following chemotherapy, adding tamoxifen to OFS reduced the risk of disease recurrence by 22% versus tamoxifen alone (HR = .78; 95% CI, 0.60-1.02). Additionally, exemestane combined with OFS demonstrated an HR for DFS of 0.65 versus treatment with standard tamoxifen (95% CI, 0.49-0.87). Premenopausal patients who are high risk may benefit from ovarian blockade, says Tripathy, noting that the toxicities tend to be short term.