376PLONG-TERM OUTCOME OF PATIENTS (PTS) WITH HER2-POSITIVE (HER2+) METASTATIC BREAST CANCER (MBC) WHO ACHIEVED A COMPLETE RESPONSE (CR) AFTER ANTIHER2 THERAPY (HER2TX).

ABSTRACT Aim: The primary objectives of this study were to analyze the long-term outcome of pts with HER2+ MBC who achieved a CR after anti-HER2 therapy (HER2Tx) and to investigate potential impact of duration of HER2Tx on remission duration. Methods: We performed a systematic retrospective review of a database of all pts with HER2+ MBC treated at our Institution with any HER2Tx. To be included in the present study pts must have received HER2Tx for at least 6 consecutive weeks and have adequate information on response and survival follow up (FU). CR was defined according to RECIST 1.1 criteria. Results: Between January 2000 and November 2013 198 consecutive pts with HER2+ MBC were commenced on HER2Tx. A total of 24 pts (12%) achieved a CR lasting for at least 6 months. Pts characteristics: median age 52yrs (range 25-68), oestrogen receptors (ER): pos 54%/neg 46%, distant metastases: visceral 50%/bone or non-visceral 50%. All pts received trastuzumab (T). Associated systemic Tx was: docetaxel + carboplatin (50%), single agent taxane (29%), docetaxel + lapatinib (13%), capecitabine 8%. All pts received continued HER2Tx post CR. Median FU is 64.5 months (12-164). At the database cut-off date (1/5/2014) 22 pts (11%) are alive and with ongoing CR. Two pts had MBC relapse while on maintenance T (at 49 and 53 months) both ER/PgR-pos. Out of 154 pts with FU > 36 months, 17 (11%) remain alive and in CR. All pts were 1st-line HER2Tx, ER-neg 59%, single site of distant metastases 71%, median duration of HER2Tx 63 months (37-127). The rate of CR > 36months among ER-neg pts is 17% (9/52). No late relapse has been observed in ER-neg CR pts who were in CR > 36 months. Conclusions: These mature results on a larger database confirm our previous (Gullo ECCO 2011) observation. Prolonged CRs after HER2Tx are not anecdotal and our data strongly suggest that overtly metastatic HER2+ MBC is a potentially curable disease, especially in pts with ER-neg disease, a limited number of metastatic sites and no prior HER2Tx. Prolonging HER2Tx might play a role in increasing durable CR. We are currently investigating the molecular profile of this subset of pts. Disclosure: All authors have declared no conflicts of interest.