Survival of stage 4 primary breast cancer cases after surgery by intrinsic subtype: HER2-positive subtype potentially curable.

e13026 Background: With the incorporation of anti-HER2 agents in the treatment of HER2 positive primary breast cancer, stage 4 disease of this subtype has become potentially curable. However, the duration of clinical CR that is needed be certain that the patient is cured, and therefore the necessary duration of anti-HER2 treatment is uncertain. We address this issue in this presentation. Methods: We present cases of stage 4 primary breast cancer who underwent breast surgery after their distant metastases were controlled, with continued post-operative systemic therapy. There were 52 cases of which the intrinsic subtype as of immunohistochemical analysis was as follows; Luminal A - 7 cases, Luminal B, - 14 cases, Luminal-HER2 - 9 cases, HER2-enriched - 7 cases, and Triple negative -15 cases. The patients were followed up for duration of treatment and overall survival. Results: The average post-operative observation period for all 52 cases was 32.6 months. The five year overall survival rate for HER2-enriched cases was 100%, for Luminal-HER2 cases 80%, for Luminal A cases 80%, for Luminal B cases 55%, and for Triple-negative cases 0%. Of the 16 HER2 positive cases (Luminal-HER2 and HER2 enriched), there was only one death at 48.4 months post-operation. The survival of 5 of 15 surviving HER2 positive cases exceed 60 months (5 years). Of the five, only one at 72.0 months has clinically observable disease (cSD). The remaining 4 cases all are clinically disease free (cCR). Of the 4 cCR cases, only 1 case which originally had multiple lung metastases is continuing anti-HER2 therapy at 90.3 months post-operation. The remaining three discontinued anti-HER2 therapy at 18.1 months (lung metastases CR, observation period 71.7 months), 72.3 months (liver and lymph node metastases CR, observation period 90.3 months), and 101.9 months (liver and bone metastases CR, observation period 102.3 months), respectively. The last case terminated anti-HER2 therapy after testing negative for ERBB2 related genes on liquid biopsy. Conclusions: With the proper incorporation of anti-HER2 therapy, Stage 4 HER2 positive primary breast cancer disease seems to be a potentially curable disease, and anti-HER2 therapy probably can be discontinued in cCR patients after 5 years. Liquid biopsy for tumor related genes (e.g. ctDNA, miRNA) might facilitate decision making.