Clinical outcomes and prognostic factors in epithelial-myoepithelial carcinoma (EMC) of the breast.

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Background: EMC is a biphasic neoplasm of the breast and comprises of malignant components derived from both luminal epithelium and myoepithelium. Most of the published data on EMC consists of individual case reports, and hence survival outcomes and prognosis are not clearly defined to guide evidence‐based management. We aimed to evaluate the clinical characteristics, survival outcomes, and prognostic factors in patients with EMC. Methods: All women with a histologic diagnosis of EMC irrespective of age and stage at diagnosis till 2018 in the National Cancer Database (NCDB) were included (N=111). Overall survival (OS) was assessed utilizing the Kaplan–Meier method and compared among groups using the log-rank test. Results: The median age at diagnosis was 67 years, and 101 (88.6%) were greater than 50 years of age. Most women were white (84.7%), non-Hispanic (91.9%), had a Charleston-Deyo score of 0-1 (95.5%), and treated at an academic or comprehensive community cancer programs (70.2%). Ten percent of patients were ER+/Her2-, 29.7% were ER-/Her2-, 0.9% were Her2+, 5.4% were ER+/Her2 unknown, 24% were ER-/Her2 unknown, and 29.7% had no data on ER status. Almost one-third of the women had poorly differentiated or undifferentiated tumors. Of the patients with available data, 46.7% had tumor ≤2 cm and more than 97% had no lymph node involvement or metastases. Most underwent surgical resection- radical mastectomy (16.2%), total mastectomy (18.9%), and partial mastectomy (56.8%). Chemotherapy and radiation were utilized in 35.2% and 40.6% of the women, respectively. At a median follow up of 67.6 months, the 3-year and 5-year OS was 81.6% and 74.3% respectively. The 5-year OS was 82.7%, 76.5%, and 50% for tumor ≤2 cm, 2-5 cm, and >5 cm respectively (p=0.009). Details on 5-year OS based on chemotherapy, radiation, and tumor size are shown in the table below. Among women who underwent lumpectomy (N=35), the 5-year OS for those who received adjuvant radiation vs surgery alone was 81.9% vs 76% (p=0.4). Conclusions: EMC demonstrates distinctive clinicopathologic features and receptor status. Administration of chemotherapy or radiation was associated with improved OS in tumors >5 cm, although small sample size and lack of recurrence data may limit this conclusion. Further studies using larger cohorts are needed to demonstrate objective efficacy of systemic treatment in lymph node positive and metastatic EMC. [Table: see text]