High HER2/Centromeric Probe for Chromosome 17 Fluorescence In Situ Hybridization Ratio Predicts Pathologic Complete Response and Survival Outcome in Patients Receiving Neoadjuvant Systemic Therapy With Trastuzumab for HER2-Overexpressing Locally Advanced Breast Cancer.

Background: The present study was performed to determine whether the human epidermal growth factor receptor-related 2 (HER2)/centromeric probe for chromosome 17 fluorescence in situ hybridization (FISH) ratio is a predictor of a pathologic complete response (pCR), recurrence-free survival (RFS), and/or overall survival (OS) in patients receiving neoadjuvant systemic treatment (NST) with trastuzumab (NST-T) for HER2+ locally advanced breast cancer (LABC).

Patients And Methods: The present retrospective study included 555 patients with HER2+ LABC who had undergone NST and definitive surgery (1999-2012); 373 had concurrently received trastuzumab. HER2-positivity was considered present with an immunohistochemical score of 3+ and/or HER2 FISH ratio of ≥2.0. We used logistic regression analysis and Cox proportional hazard modeling to determine whether a high HER2 FISH ratio, either as a continuous variable or with a cutoff of ≥7.0, would predict for pCR (no invasive disease in the breast and no tumor in the ipsilateral axillary lymph nodes), RFS, and/or OS.

Results: The pCR group's median HER2 FISH ratio was significantly higher than that of the non-pCR group (6.4 vs. 5.2; p = .003). The logistic regression model demonstrated that the independent predictors of pCR included a high HER2 FISH ratio as a continuous variable (p = .04). The multicovariate Cox proportional hazard model showed that a high HER2 FISH ratio (with a cutoff of ≥7.0 or as a continuous variable) was a significant prognostic indicator of longer RFS time (p = .047 and p = .04, respectively). Similarly, a high HER2 FISH ratio of ≥7.0 was associated with longer OS (p = .06).

Conclusion: A high HER2 FISH ratio is a predictor of pCR in patients with HER2+ LABC who receive NST-T.

Implications For Practice: This study demonstrated the optimal predictive and prognostic value of a HER2/centromeric probe for chromosome 17 FISH ratio for primary HER2+ breast cancer treated with trastuzumab combined with neoadjuvant systemic treatment (NST-T). This suggests that a high HER2 FISH ratio is a potential indicator for a high pathologic complete response rate and a better prognosis when patients are treated with NST-T.