OBJECTIVETo investigate the effect of risk factors on ipsilateral breast tumor recurrence (IBTR) and distant disease-free survival (DDFS) for patients with triple-negative breast cancer (TNBC) who underwent breast-conserving treatment (BCT).

METHODSA series of 1 835 patients with primary breast cancer treated with BCT in a single institute between December 1999 and August 2010 were analyzed retrospectively. Totally 1 614 patients, whose characteristics were intact, were analyzed to compare their outcomes with respect to the incidence of IBTR, DDFS and disease-free survival (DFS). All of patients were female. Median age was 47 years (ranging 21 to 92 years, interquartile range 14 years). According to the immunohistochemical results of the patients, 1 614 cases were divided into TNBC group (n=308) and non-TNBC group (n=1 306). The risk factors of relapse after breast-conserving treatment (age at diagnosis, spread to axillary lymph nodes, hormone receptor status, neoadjuvant chemotherapy, and maximal tumor diameter, human epidermal growth factor receptor 2 (HER-2) status, preoperative MRI, the location and extent of the tumor bed defined by CT scans for electron boost planning as part of breast radiotherapy) were studied.χ(2) test was used to compare the distribution of baseline characteristics among subtypes. The probability of survival (or relapse occurrence), and DDFS were calculated using the Kaplan-Meier method. Cumulative incidence functions were used to describe the cumulative hazard from LR, IBTR and DDFS in the presence of competing risks.

RESULTSA total of 1 614 women with primary breast cancer underwent a breast-conserving surgery followed by radiotherapy. The median follow-up period was 77 months (interquartile range 36 months). One hundred and forty patients (8.6%) were lost to follow-up. Overall 5-year IBTR rate was 3.1% (95% CI: 2.2% to 4.0%), 5-year DDFS rate was 95.8% (95% CI: 94.9% to 96.7%) and 5-year DFS rate was 93.8% (95% CI: 92.7% to 94.9%). Lymph nodal involvement (HR=3.03, 95% CI: 1.66 to 5.51, P=0.000) and use of CT information in boost field planning (HR=0.40, 95% CI: 0.20 to 0.80, P=0.010) were associated significantly with IBTR in Cox multivariable analysis. Multivariable analysis showed that TNBC doesn't have a significantly increased risk of IBTR compared with the non-TNBC subtype (HR=0.90, 95% CI: 0.50 to 1.76, P=0.78). TNBC was not an independent risk factor for DDFS or DFS. The multivariable model showed significant effect of nodal status and age at diagnosis on 5-year DDFS rate and 5-year DFS rate.

CONCLUSIONSBreast-conserving treatment for TNBC is not associated with increased IBTR compared with non-TNBC subtype. Use of CT information in boost field planning can reduce the risk of ipsilateral breast tumor recurrence for patients undergoing BCT.