Criteria for the decision to treat small tumors in adjuvant setting remain debatable, especially for HER2-positive tumors, since HER2 itself is associated with poor prognosis. Analysis of a large database including 503 T1 HER2-positive breast carcinomas treated with chemotherapy plus trastuzumab in Italian oncology clinics from 2006 to 2009 and, with 32 months of median follow-up and with 35 (7.0%) relapses, revealed no statistically significant differences in relapse rate among the T1a/T1micro, T1b and T1c groups, suggesting that tumor size is not associated with relapse probability in T1 HER2-positive tumors; the only clinico-pathological factors significantly associated with disease-free survival were nodal involvement (unadjusted HR = 3.4, 95%CI = 1.6-7.3, p = 0.002), loss of hormone receptor expression (HR = 3.1, 95%CI = 1.5-6.2, p = 0.002) and high tumor grade (HR = 2.9, 95%CI = 1.2-6.9, p = 0.020). Multivariate analysis indicated that patients who were both ER-negative and lymph node-positive presented the highest risk of relapse (HR = 5.5, 95%CI = 2.8-10.9, p = <0.001). These results suggest that the clinical decision for adjuvant treatment of small HER2-positive tumors should be based on nodal and hormone status, not on tumor size information. While the most recent National Comprehensive Cancer Network guidelines (version 3.2012) for systemic adjuvant treatment of small HER2-positive breast cancer only suggest considering adjuvant chemotherapy treatment including trastuzumab for T1a cases with axillary node micrometastasis and for all T1b, but require such treatment for all tumors >1 cm, our data identify T1 tumor ER-negativity/axillary lymph node-positivity as the crucial criteria for adjuvant treatment, independent of tumor size categories.

Supported by AIRC.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-12-06.