Trends in Estrogen Receptor Testing and Tamoxifen Initiation After Ductal Carcinoma in Situ During 1996–2011

Background/Aims: Ductal carcinoma in situ (DCIS), a stage 0 breast cancer usually detected on mammogram, accounts for 24% of all breast cancer diagnoses. In 2000, tamoxifen was FDA-approved as adjuvant endocrine therapy for DCIS patients. We assessed tamoxifen initiation after DCIS diagnosis according to calendar year, tumor characteristics and concurrent treatment within Group Health Cooperative (GHC). Methods: We identified female GHC enrollees aged 18–89 years with an incident DCIS diagnosis during 1996–2011. Eligibility criteria required 12 months continuous enrollment before and after DCIS diagnosis. Tamoxifen initiation was identified through pharmacy records. Tumor characteristics and treatment information were captured from the virtual data warehouse. Relative risks (RR) and 95% confidence intervals (CI) for tamoxifen initiation were calculated with multivariable generalized linear models adjusted for age, calendar year, estrogen receptor (ER) status, radiation therapy and grade. Results: We identified 727 women with a DCIS diagnosis, including 163 (22%) who initiated endocrine therapy within 12 months. Fourteen women filled aromatase inhibitor prescriptions and were analyzed with tamoxifen users. ER testing increased from 4% of DCIS cases in 2001 to 71% in 2011. Women diagnosed with DCIS during 1996–2000 were 43% less likely to use tamoxifen as those diagnosed in 2001–2005 (RR: 0.6, CI: 0.4–0.9). However, tamoxifen use did not vary significantly across calendar years after 2001. Among ER-positive tumors, 58% (18 of 31) used tamoxifen in 2001–2005 compared to 39% (47 of 122) in 2006–2011. Among women with unknown ER status, 24% (47 of 194) used tamoxifen in 2001–2005 compared to 15% (21 of 140) in 2006–2011. Younger women were more likely to use tamoxifen (RR: 1.7, 95% CI: 1.1–2.6 for age 45–54 compared to 65–74; P-trend=0.0002). Compared to breast conserving surgery (BCS) with radiation, women who had BCS without radiation (RR: 0.5, CI: 0.2–0.9) or mastectomy (RR: 0.6, CI: 0.4–0.8) were less likely to use tamoxifen. Six percent (n=47) of women had a bilateral mastectomy; of these, \u3c 5 used tamoxifen. Discussion: Increasing ER testing since 2001 has not corresponded to parallel increases in tamoxifen use. Tamoxifen use after DCIS was more common among younger women and those who had BCS and radiation therapy