To compare the clinical characteristics and treatment methods of mucinous breast carcinoma (MBC) and breast invasive ductal carcinoma (BIDC), and analyze prognostic factors.

The clinical data of 100 patients with MBC and 100 patients with BIDC in the Department of Breast Surgery, Cancer Hospital, Chinese Academy of Medical Sciences from January 2010 to December 2014 were retrospectively analyzed. The clinicopathological characteristics were compared between two groups using t test, rank sum test, χ² test or Fisher’s exact test. Survival curves were drawn by Kaplan-Meier method, and DFS and OS were compared between two groups by log-rank test. Univariate and multivariate Cox proportional hazards models were used to analyze related factors affecting DFS and OS.

There were significant differences in age, TNM stage, histological grade, molecular typing and surgical methods between MBC group and BIDC group (t=1.297, Z=3.567, -8.627, χ²=10.086, 17.737; all P<0.050). A total of 14 cases were lost to follow-up, including 3 cases in MBC group and 11 cases in BIDC group, with the follow-up rate of 93% (186/200). There were 12 deaths, including 2 in MBC group and 10 in BIDC group. The 5-year DFS was 91% in MBC group and 78% in BIDC group, indicating a significant difference (χ²=7.585, P=0.006). The 5-year OS was 97% in MBC group and 88% in BIDC group, indicating a significant difference (χ²=7.752, P=0.005). The DFS in MBC group was significantly better than that in BIDC group (HR=0.30, 95%CI: 0.13-0.69, P=0.004); the risk of DFS in luminal B subtype (HER-2 positive) was 4.97 times as high as that of luminal A subtype (95%CI: 1.71-14.42, P=0.003), HER-2 overexpression subtype 6.08 times (95%CI: 2.22-16.13, P<0.001); the risk of DFS in patients receiving modified radical mastectomy was 0.36 times as high as that in patients who received breast-conserving surgery+ sentinel lymph node biopsy (95%CI: 0.13-0.99, P=0.047). The OS in MBC group was significantly better than that in BIDC group (HR=0.26, 95%CI: 0.10-0.63, P=0.003); the risk of OS in patients with luminal B subtype (HER-2 positive) was 6.90 times as high as that of luminal A subtype (95%CI: 1.72-27.67, P=0.006), HER-2 overexpression subtype 11.44 times (95%CI: 3.13-41.89, P<0.001), triple-negative subtype 6.46 times (95%CI: 1.57-26.51, P=0.010); the risk of OS in patients receiving modified radical mastectomy was 0.21 time as high as that in patients who received breast-conserving surgery + sentinel lymph node biopsy (95%CI: 0.06-0.74, P=0.015).

The patients with MBC have a better prognosis and longer survival compared with patients with BIDC, which is related to the molecular subtype.