Differences in the clinicopathological characteristics of pure and mixed invasive micropapillary breast carcinomas from eastern China

BACKGROUND: Invasive micropapillary carcinoma of the breast (IMPC) is a rare pathologic subtype of breast cancer. Since the differences in the pathological features of pure and mixed IMPCs are not fully understood, we aimed to investigate the difference in clinicopathological characteristics between localized pure and mixed IMPCs. METHODS: A total of 121 localized IMPC cases were included. The clinicopathological features and survival estimates of the pure IMPC and mixed IMPC groups were compared. Targeted sequencing was performed to investigate the genomic profile of paired primary breast cancer and metastatic tissue samples from two pure IMPCs and four mixed IMPCs. RESULTS: Overall, 48 cases were pure IMPC and 73 were mixed IMPC. The pure group had a significantly higher proportion of Luminal B compared to the mixed group (37.5% vs. 15.1%). The pure group had a similar HER2 overexpression rate (31.2% vs. 32.9%) and mean age at diagnosis (51.0 vs. 50.2 years), compared with the mixed group. The pure group had a significantly higher proportion of stage IIIC cases compared with the mixed group (38.3% vs. 17.8%). We found no significant difference in the 3-year disease-free survival (DFS) between the two groups (83.7% vs. 80.0%), but the mixed group had a better overall survival (OS) compared with the pure group [HR =0.28 (0.091–0.868), P=0.047]. CONCLUSIONS: We found that pure IMPC had a more aggressive behavior with locally advanced disease and a higher proportion of Luminal B than mixed IMPC. Mixed IMPC had a longer OS compared to pure IMPC, but there was no significant difference in the 3-year DFS between the two groups.