Risk factors of ipsilateral breast tumor recurrence in triple-negative or HER2-positive breast cancer patients who achieved pathological complete response after neoadjuvant chemotherapy.

e12599 Background: To date, patients undergo breast surgery after neoadjvant chemotherapy (NAC) even though they achieve clinical complete response (cCR). The safety of omitting breast surgery for the patients who are predicted to be pCR has recently investigated in some research, however we still have not reached to a definite consensus yet. We may consider the breast surgery omission on the assumption that the rate of ipsilateral breast tumor recurrence (IBTR)after achieving pCR is acceptably low. The purpose of this study is to examine the rate of and evaluate the clinical features of IBTR in patients achieving pCR after NAC. Methods: In this study, a total of 278 patients with HER2-positive or Triple negative type primary breast cancer were enrolled from4 institutions. They were all diagnosed as ypT0 after breast conserving surgery and received postoperative radiotherapy. Occurrence of IBTR and other clinicopathological factors were collected by retrospective chart review. Results: Of the 278 patients, 49 patients (18%) were ER+/HER2+, 106 patients (38%) were ER-/HER2+ and 123 patients (44%) were ER-/HER2-. We found breast recurrence in 11 patients (4%) as a first recurrence. The 5-year breast recurrence rate was 4.5% in total, 2.2% in ER+/HER2+, 4.0% in ER-/HER2+ and 4.6% in ER-/HER2-, respectively. There was no significantly difference among subtypes. Interestingly, the 5-year breast recurrence rate of patients under 40-year-old was 12.3% which was significantly higher than patients with and above 40-year-old (3.1%, p=0.002). Conclusions: We should be extremely careful when consider omitting breast surgery for patients younger than 40 even if they achieved pCR after NAC.