Long-term toxicity profile of trastuzumab emtansine (T-DM1): A multicenter real-life study.

e12507 Background: T-DM1 is widely used in HER2 positive metastatic breast cancer (MBC) patients (pts), often for many cycles until progression. However, little is known about its long term toxicity. The aim of this study was to evaluate the safety profile of T-DM1 when delivered for ≥12 cycles. Methods: HER2 positive MBC pts who had received ≥12 cycles of T-DM1 across 18 Italian cancer centers were enrolled from January 2017 to September 2018. The 12 cycles cut-off was chosen based on the EMILIA trial median PFS (9.6 months), to identify a patient population treated with T-DM1 for longer time. Tumor and clinical characteristics were collected. Standard haematological tests, blood chemistries and side effects (nausea, vomiting, diarrhea, stomatitis, asthenia) were recorded cycle by cycle, according CTCAE criteria version 4. Haematological and laboratory toxicities were available for 86 patients, while other toxicities for all 115 patients. Results: Overall, 115 pts were enrolled. Median age was 54.5 (range 29.6–81.9); median time from diagnosis of metastatic disease to first T-DM1 cycle was 32.5 months. T-DM1 was administered as 2nd line and 3rd line of treatment in 45.2% and 27.8% of pts, respectively. Median number of cycles was 18 (range 12-59). Complete response, partial response and stable disease rates were 11.4%, 43% and 45.6%, respectively. Treatment related side effects are shown in table 1. Interestingly, no increased liver toxicity was observed in pts with liver metastases. Analysis of mean CTCAE grade by cycle showed that no relevant incremental toxicity was observed during long term T-DM1 therapy. Conclusions: T-DM1 is safe and well tolerated in these long responding pts. We found no relevant cumulative toxicity. Patients should be treated with T-DM1 as long as their tumor responds, as no safety issues are related to its long term use. [Table: see text]