Rare triple-negative breast cancers (TNBC): An NCDB analysis.

e19253 Background: The literature on rare triple negative breast cancer (TNBC) histology types is sparse; herein we present the clinical demographic and treatment patterns as well as overall survival (OS) for rare (< 10%) types of breast cancers that typically present as TNBCs: Medullary carcinoma (MedC), Adenoid cystic carcinoma (ACC), and Metaplastic breast cancer (MetC). Methods: Records of patients with a confirmed diagnosis of MedC, ACC, and MetC between 2010 and 2016 in the National Cancer Database (NCDB) were analyzed. Patients with an unknown stage were excluded. Univariate analyses and multivariable Cox-regression models were performed in SAS v. 9.4. Results: A total of 8,479 records were analyzed. MetC was the most commonly diagnosed histologic type in our cohort with 6,867 (81%) patients versus 255 (3.0%) MedC patients and 1,357 (16%) ACC patients. MedC presented earlier in life, with a median age of 53 years versus 62 years for ACC patients, and 63 years for MetC patients. The proportion of TNBC varied by histology type for MedC (70.4%), ACC (77.0%), and MetC (79.0 %). Patients with ACC were less likely to receive radiotherapy (52.4%) and chemotherapy (12.9%) compared to MedC (61.2%, 74.5%) and MetC (49.7%, 68.6%) respectively. On Cox multivariate regression, age ≥60 (HR 4.7), stage ≥3 [compared to patients with stage 0&1] (HR 5.7), and not receiving radiotherapy (HR 2.0) or chemotherapy (HR 1.25) conferred worse overall survival for MedC. Similarly, among patients with ACC, age ≥60 (HR 3.5), stage ≥3 (HR 5.3), and lymph node involvement (HR 4.8) were adverse prognostic indicators as well as not receiving radiation therapy (HR 1.47). Among MetC, lung metastasis (HR 2.6), stage ≥3 (HR 4.5), but also not receiving chemotherapy (HR 1.8) or radiation therapy (HR 1.47) was associated with worse survival outcomes. All p-values for cox regression is <0.0001. The 5-year OS was 92.6% for patients with MedC, 92.0% for ACC patients, 69.3% for MetC patients; all p-values <0.0001. Conclusions: This analysis describes rare types of TNBCs: MedC (most common), ACC, and MetC. We noted heterogeneity among these 3 rare types of TNBC, with the worst 5-year OS noted for MetC. Poor prognostic factors for MetC include advanced stage, lung metastasis, older age, and not receiving chemotherapy or radiation therapy. Future research focusing on rare subtypes of breast cancer is desirable and would potentially inform the optimal management of these breast carcinomas.