HER2-positive breast cancer cells percentage and progression to trastuzumab treatment in metastatic patients

Abstract

11510 Background: Immunohistochemistry (IHC) assay for HER2 in breast cancer (BC) identify patients (pts) who are at benefit from Trastuzumab (T) therapy. The percentage (%) of positive cells is not known to have prognostic significance. Methods: We analyze pts that received T as a treatment for metastatic BC in our center, in monotherapy or in combination with other agents, and to ascertain whether the % of her-2 positive cells can be a predictive factor of response to therapy with T. We define HER-2 positive cells according to the Envision method 3+, valuating the percentage of cells with positive result. If the result of the IHC was 2+, we use fluorescence in situ hybridation (FISH). For a total of 36 patients treated, the results of the % were available only for 21 patients. The median of positive cells was 90% (range 30–100%) and it was taken to define low percentage of positive cell tumors (LPPCT) or high percentage of positive cells tumors (HPPCT). We evaluated the initial response (disease progression-stability versus parcial-complete response), the time to progression (TTP) and the overall survival (OS) of pts on T. We used the log-rank test to determinate the TTP and Fisher’s exact text to determinate the initial response and the OS on therapy with T. Results: TTP to T was significantly higher in LPPCT (median 19 months, CI 10–28) than in HPPCT (median 13 months, CI 7–19) (p=0.037). We didn’t find significant differences regarded to baseline characteristics of the patients, response nor OS. Conclusions: We find that the % of HER2-positive cells is significantly correlated with the TTP in patients on T therapy. The percentage of HER2-positive cells can be at clinical interest as a predictive factor of response to her-2 targeted therapy and it must be confirmed with a large number of pts. No significant financial relationships to disclose.