The impact of molecular status on survival outcomes for invasive micropapillary carcinoma of the breast.

Invasive micropapillary carcinoma (IMPC) is an uncommon variant of breast cancer. Previous studies demonstrated this subtype is often hormone receptor (HR)-positive, resulting in survival outcomes similar to invasive ductal carcinoma. However, many of these studies were conducted prior to HER2 testing availability. We aim to determine the impact of molecular marker status (including HER2 status) on IMPC survival outcomes. The National Cancer Data Base (NCDB) was used to retrieve patients with biopsy-proven IMPC from 2007 to 2012. Only patients with known HR and HER2 status were included. Cox multivariate regression was used to determine prognostic factors. In total, 865 patients were included; median follow-up was 2.5 years. Overall, 651 patients (75.3%) had HR + HER2- disease, 128 (14.8%) had HR + HER2+ disease, 41 (4.7%) had HR-HER2 + disease, and 45 (5.2%) had triple negative disease. Patients with triple negative disease were more likely to have poorly differentiated histology (66.7%), lymphovascular invasion (73.3%), stage 3 disease (37.8%), undergone mastectomy (68.9%), and positive surgical margins (15.6%). On Cox multivariate regression, those with triple negative disease had worse overall survival (hazard ratio [HR] 7.28, P < 0.001). Other adverse prognostic factors included African-American descent (HR 2.24, P = 0.018), comorbidity score of 1 (HR 2.50, P = 0.011), comorbidity score ≥2 (HR 3.27, P = 0.06), and ≥3 positive lymph nodes (HR 3.23, P = 0.007). Similar to invasive ductal carcinoma, triple negative disease in IMPC results in worse survival outcomes. This is the largest and first study to characterize molecular status (including HER2 status) in patients with IMPC and its impact on survival outcomes.