Long-term follow-up (FU) of patients with durable complete response (DCR) after chemotherapy (CT) and trastuzumab (T) for HER2-altered (HER2+) metastatic breast cancer (MBC).

Abstract

615 Background: Durable CT-induced complete response (DCR) of MBC is reported only anecdotally. The addition of monoclonal antibody T to conventional CT results in significant increase in response rates and prolonged survival for patients (pts) with HER2+ MBC. Though CRs are reported in most phase II and III clinical trials of CT+T, there is lack of data about clinical features and long-term outcome of these pts. Methods: We retrospectively reviewed all pts with HER2+ MBC treated at our Institutions with any CT+T and identified cases who achieved DCR. HER2 positivity was defined as 3+score at immunohistochemistry and/or amplification at FISH test. DCR was defined as a CR according to RECIST 1.0 criteria lasting >36 months. Results: We identified 13 pts with HER2+ MBC who met criteria for DCR following CT+T. Their characteristics are: median age: 56yrs (range 30-65), stage at diagnosis: M0 54%/M1 46%, histology: ductal 84%/mixed ductal-lobular 8%/unknown 8%, tumour grade: G3 54%/G2 23%/unknown 23%, oestrogen receptors (ER): neg 62%/pos 38%, sites of metastatic disease: liver only 54%/other visceral 15%/bone and soft tissues only 31%, chemotherapy regimen: taxane+carboplatin 54%/single-agent taxane 23%/docetaxel+lapatinib 15%, capecitabine 8%. Metastatic disease was biopsy-proven in 54% of pts. All pts received maintenance T. Median follow-up (FU) is 6.5 yrs (range 3.0-11.6). Median duration of T was 59 months (17-121). At database cut-off date 12 pts (92%) are alive. Five pts (38%) had disease relapse (3 on maintenance T, 2 after T discontinuation), 2 of whom had radical surgery. In 8 pts (62%) disease has not relapsed (characteristics: all 1st-line therapy, ER negative 75%, liver only distant disease 75%). Conclusions: This is the largest series to our knowledge analyzing long-term FU of HER2+ MBC pts with DCR following CT+T. DCR pts appear to have prolonged survival and a substantial subgroup of them have no further disease relapse. These pts are usually treated in the 1st-line setting, have more frequently ER-negative disease and liver-only metastases. We are currently investigating the molecular profile of this subset of pts.