Adherence to hormonal therapy after surgery among older women with ductal carcinoma in situ: Implications for breast cancer-related adverse health events.

Background: Evidence from randomized clinical trials (RCTs) shows that receipt of hormonal therapy after surgery for estrogen receptor-positive ductal carcinoma in situ (DCIS) reduces the risk of DCIS and contralateral invasive breast cancer (IBC) but not death from breast cancer. RCTs examined homogeneous samples, and therefore whether this evidence can be generalized to diverse populations is unclear.

Methods: Population-based data from four state cancer registries (California, New Jersey, New York, and Texas) were analyzed on women aged 65 years and older newly diagnosed with DCIS who underwent surgery with or without radiation during the years 2006-2013. Registry records were merged with Medicare enrollment in Parts A and/or B and D (prescription drugs) and associated claims. Whether adherence to hormonal therapy was associated with adverse breast cancer-related health events was analyzed.

Results: Achieving excellent adherence did not affect death from breast cancer. In contrast, the risk of developing a subsequent breast tumor was 6.24 percentage points (breast-conserving surgery [BCS] with radiation therapy [RT]) and 10.54 percentage points (BCS alone) lower for women with excellent versus low adherence (p < .00001). For excellent versus good adherence, the reduced risk among women who had BCS with and without RT was approximately 3 and 5 percentage points, respectively. A similar pattern emerged for the risk of IBC among women who achieved excellent versus good or low adherence, whereas good versus low adherence comparisons were not significant.

Conclusions: This analysis of a diverse population-based cohort of women with DCIS demonstrates that achieving excellent adherence to hormonal therapy is critical to minimizing the occurrence of developing subsequent breast tumors.

Plain Language Summary: Our analysis of a diverse population-based cohort of women with ductal carcinoma in situ demonstrates that achieving excellent adherence to hormonal therapy is critical to minimizing the occurrence of developing subsequent breast tumors.