Myoepithelial carcinoma: A National Cancer Database study of demographic and socioeconomic factors.

Abstract

e22590 Background: Myoepithelial carcinoma (MECA) is a rare malignant tumor arising from myoepithelial cells and documented across multiple anatomical sites, most commonly in the breast and salivary glands. Due to its low incidence, the epidemiology and clinical characteristics of MECA remain poorly understood. This study aims to use population-level datasets from the National Cancer Database (NCDB) to better characterize demographic distribution, tumor characteristics and treatment patterns for MECA. Methods: This study examined histologically-confirmed MECA cases (ICD-O-3 code - 8982) in the National Cancer Database (NCDB) from 2004–2020 (N = 336). Variables included age, sex, race, facility type, distance from facility, insurance, Hispanic status, educational attainment, Charleson-Deyo comorbidity score, survival rates, and treatment modalities. Descriptive statistical testing and regression analysis were used to assess demographic trends. Results: A gradual upward trend in the number of reported cases of MECA was observed over this study period (R² = 0.22). Women were disproportionately affected (70.5%), and the average age at diagnosis was 56.7 years. Most patients were White (82.1%) and non-Hispanic (89.3%), and the majority had a Charlson–Deyo score of 0 (78.9%). The most common primary site was the upper outer quadrant of the breast (12.5%), followed by the overlapping lesion of the breast (10.7%) and the vulva (5.4%). Nearly half were privately insured (47.0%), and 39.3% were covered by Medicare. Most patients lived in metropolitan counties (81.5%) and 40.5% were in the highest income quartile ($74,063 or more). Patients were most frequently treated at academic or research programs (39.2%) and comprehensive community cancer programs (32.2%). Many patients received surgical procedures (77.9%), followed by radiation therapy (36.6%). After surgery, 68.2% had no residual tumor, 3.3% had a microscopic residual tumor, 2.75% had an unspecified residual tumor, and 0.6% had a macroscopic residual tumor. Two-year survival was 79.4%, five-year survival was 66.5%, and ten-year survival was 52.0%. Conclusions: To our knowledge, this is the first NCDB analysis of myoepithelial carcinoma, demonstrating a clear predominance among women and identifying the upper outer quadrant of the breast as the most common primary site. This study also provides the first population-level assessment of socioeconomic factors in MECA, showing that patients most often reside in densely populated metropolitan areas and fall within the highest income quartile. These insights expand the limited epidemiologic understanding of MECA and highlight the need for further research on how demographic and socioeconomic factors influence diagnosis, treatment, and outcomes.