Abstract P6-07-34: Disease-related outcomes with adjuvant chemotherapy in HER2 positive or triple negative T1a/bN0 breast cancers

Background: Previous studies reported higher relapse rates in T1a/bN0 breast cancers characterized by high-risk biology (HER2 positive or triple negative). The benefits of adjuvant chemotherapy in this group have not been evaluated. The purpose of our study was to determine potential impact of chemotherapy on incidence of relapses and to define the population appropriate for treatment based on observational data.

Methods: We pooled data from two multi-institutional databases spanning the period of 1996–2008 (Beth Israel Medical Center) and 2000–2010 (Brown University). We fitted a propensity score model to adjust for unbalanced confounders between the groups treated or untreated with adjuvant chemotherapy and, in case of HER2+ disease, with trastuzumab. Competing risk analysis was employed to study the effect of chemotherapy on cancer relapses in the matched population.

Results: The study included 321 patients (160 from Beth Israel and 161 from Brown) with a median age of 57 years (range 28–88). 111 (35%) cases were triple negative (TN) and 210 (65%) were HER2+ (of which 64% were ER+). 41% patients received adjuvant chemotherapy and 22% of HER2+ cases received trastuzumab. The treated group differed from untreated with regards to distribution of age, menopausal status, year of diagnosis, histological subtype and grade, tumor size, rates of mastectomy, and adjuvant endocrine therapy. All confounders were successfully balanced with the propensity score analysis. With a median follow-up of 56 months, 20 relapses (12 locoregional and 8 distant) and 10 unrelated deaths occurred. The cumulative incidence of relapse at 5 years was 7.3% (95% CI, 4.3–11.4) and relapse-free survival was 90.2% (95% CI, 85.2–93.6). Age less then 35 years (46.4% vs. 6.1%, p = 0.0004) and TN status (12.9% for TN versus 4.8% for HER2+, p = 0.03) were associated with higher risk of relapse. No significant differences with regards to tumor size (T1a or T1b), surgery type and other variables were observed. There was no significant effect of chemotherapy on incidence of relapse (Hazard ratio 1.2, 95% CI 0.34–4.23, p = 0.78), relapse-free survival or distant recurrence-free interval after propensity score adjustment. Additionally in the HER2+ patients, no benefit of trastuzumab was detected (hazard ratio 0.78, 95% CI 0.06–9.85, p = 0.85). Adjuvant endocrine therapy was associated with lower risk of relapse in the ER+ subgroup (p = 0.04).

Conclusion: Survival outcomes in very early stage breast cancer are excellent with current therapy even in biologically aggressive subtypes. Triple negative status and very young age correlate with higher incidence of relapse. While adjuvant endocrine therapy may be effective in ER positive subset, the risk/benefit ratio of chemotherapy with or without trastuzumab remains uncertain.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-07-34.