Difference in clinicopathological characteristics between pure and mixed invasive micropapillary breast carcinomas from eastern China.

Abstract

e12500 Background: Invasive micropapillary carcinoma of the breast (IMPC) is a rare pathologic subtype of breast cancer with frequent lymph node metastases. Since the differences in pathological features between pure and mixed IMPCs are not fully understood, we aimed to investigate the difference in clinicopathological characteristics between pure and mixed IMPC. Methods: Overall 121 IMPC cases were included from Zhejiang Cancer Hospital, China during May 2010-August 2018. The clinicopathological features and survival estimates between 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 IMPC and four mixed IMPC. The copy number variations (CNVs) and the tumor mutation burden (TMB) from metastatic tissues were analyzed. Results: Overall 48 cases were pure IMPC and 73 were mixed IMPC. The pure group had significantly higher proportion of luminal B compared to the mixed group (37.5% vs.15.1%), but lower proportion of luminal A (33.3% vs. 45.2%). The pure group had similar HER2 overexpression rate (31.2% vs. 32.9%) and mean age at diagnosis (51.0 vs. 50.2 years), compared to the mixed group. The pure group had significant higher proportion of stage ⅢC cases compared to the mixed group (38.3% vs.17.8%). We found no significant difference in 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 to the pure group (HR = 0.28 (0.091-0.868), P = 0.047). Conclusions: We found that pure IMPC had more aggressive behavior with locally advanced disease and higher proportion of luminal B than mixed IMPC. Mixed IMPC had a longer OS compared to pure IMPC, but no significant difference in 3-year DFS between two groups.