Significance of chromosome 17 polysomy in breast cancer.

Abstract

e12002 Background: Human epidermal growth factor receptor 2 (HER-2) overexpression occurs in up to 30% of breast cancers and has been associated with poor clinical outcomes that have improved with advances in HER-2 directed therapy. The HER-2 gene resides on the long arm of chromosome 17 and amplification is typically assessed via immunohistochemistry or fluorescence in situ hybridization (FISH); HER-2 is interpreted as amplified, non-amplified, or equivocal. The effect and clinical impact of chromosome 17 polysomy in specimens interpreted as HER-2 non-amplified has not been well-established in breast cancer patients. This subgroup may represent a unique set of patients who may benefit from HER-2 directed therapy given the increase in HER-2 gene copy number. If tumors with polysomy 17 share biologic similarities with those positive for HER-2 amplification this may significantly influence the approach to treating these patients. In a single institution study we reviewed all breast cancer cases diagnosed in 2008 which were reported as HER-2 equivocal or non-amplified via FISH and with chromosome 17 polysomy in order to extrapolate disease-free and overall survival data within this subset. Methods: HER-2 expression via FISH from patients diagnosed with breast cancer in 2008 was reviewed. In those patients with equivocal or non-amplified HER-2 expression we selected those with chromosome 17 polysomy defined as a chromosome 17 centromere copy number of > 3 per tumor cell. A total of 9 patients were identified. Results: The median age was 74 (36-88). Median tumor size was 1.6 cm (0.7-4.9) and 8 patients (88%) had both estrogen and progesterone positive tumors. Stage distribution was as follows: stage IA: 4 (44%); stage IIA: 2 (22%); stage IIB: 2 (22%) and stage IIIA: 1 (11%). The actuarial 3 year disease free survival was 67%. Conclusions: Breast cancers with equivocal or non-amplified HER-2 expression with chromosome 17 polysomy represent a unique subset of tumors with a biology that is not well-understood. Previously published studies have yielded conflicting results regarding the prognostic significance of this genotype. Our study reflects a three year survival of 67% which suggests that these patients represent an aggressive subset.