Chromosome enumeration probe 17 (CEP) ratio to predict chemosensitivity in HER-2 overexpressing breast cancer

Abstract

e11600 Background: Precise assessment of HER-2 is critical in breast cancers and predicts benefit of trastuzumab (T). Although subset analysis of CALGB 9840 suggests benefit in FISH-negative patients with chromosome 17 polysomy (C17), clinical significance of C17 in FISH-positive patients is still less known. To analyze the epidemiologic feature of C17 in Japanese patients, consecutive operable breast cancer patients during 05–07 treated in single institution were studied. Methods: HER-2 status of consecutive 307 patients excluding DCIS and whose specimens were poor quality for study, were analyzed with Pathvysion (FISH). We defined HER- 2 (+) and C17 as HER-2/chromosome 17 ratio ≥ 2.2 and CEP ratio ≥ 2.2, respectively. Pathological response following neoadjuvant chemotherapy (NACT) was assigned according to the Japanese Breast Cancer Society (G3; no invasive or in situ residual tumor in the breast, G2; up to two thirds of primary cancer cells having pathologically severe changes or disappearance, G1; up to one third to two thirds of primary cancer cells having pathologically severe changes or disappearance). Results: HER-2 (+) was found in 22% (67/307) and C17 in 25% (77/307). Twenty-four of 67(36%) in HER-2 (+) had C17 and 53 of 240 (22%) in HER-2 (-) did C17. Among HER-2 (+), 23 cases received T-contained regimens as NACT (FEC/EC followed by PAC+T in 18 and DOC+CPA+T in 5). Six of 9 (67%) with C17 had G3 and 2 of 14 (14%) with non-C17 did G3. CEP ratio significantly predicts to have G3 (p=0.02) but HER-2/chromosome 17 ratio by logistic regression analysis. Conclusions: C17 was found in 25% of Japanese operable breast cancer patients of which was similar to that of CALGB. CEP ratio is a good predictive marker for chemo- sensitivity in HER-2 (+) subset. No significant financial relationships to disclose.