Unique characteristics and failure patterns of metaplastic breast cancer in contrast to invasive ductal carcinoma: A retrospective multicenter case-control study (KROG 13-07)

Background This retrospective study was performed to investigate the need for management modification in MBC according to evaluation of characteristics and failure patterns compared with IDC. Patients and Methods We performed this multicenter study taking MBC and randomly assigned IDC cases matched for age (± 3 years), pathologic stage (T and N), locoregional treatment methods (surgery with or without radiation therapy), and period of treatment (± 6 months) that occurred from January 1999 to November 2011 in the 6 institutions of the Korean Radiation Oncology Group. Results A total of 144 female MBC patients were enrolled. The median follow-up was 51 months (range, 1-186 months). The rates of positivity for estrogen receptor (P <.001), progesterone receptor (P <.001), and HER2 (P =.007) were significantly lower in MBC patients. During follow-up, recurrence developed in 22 (15.3%) MBC and 6 (4.2%) IDC patients (P =.002). The median time to recurrence of MBC and IDC was 15 months and 24 months, respectively. Most instances of recurrence in MBC developed in the triple-negative (TN) subgroup (TN-MBC). In particular, locoregional recurrence developed exclusively in the TN-MBC subgroup. In the TN-MBC subgroup, the number of risk factors (pT2-3, N1-3) was related to significant differences in overall survival (P =.001) and recurrence-free survival (P <.001). Conclusion The MBC patients had a higher rate of TN, poorer differentiation, and a higher recurrence rate than did the IDC patients. Considering the unique characteristics and failure patterns, it is necessary to modify the current management guidelines for MBC.