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.