Patterns of Care and Survival of Metastatic Metaplastic Breast Cancer Patients.

Background: Metaplastic breast cancer (MBC) is a rare, aggressive variant of breast cancer, usually triple negative disease and chemotherapy refractory. Despite this, the standard of care remains the same as invasive ductal breast cancer. We sought to analyze patterns of care and outcomes among patients with metastatic MBC.

Methods: Patients over 18 years diagnosed with metastatic MBC from 2004-2015 were identified in the National Cancer Database (NCDB). Clinical and demographic details were compared between two groups (chemotherapy vs no chemotherapy). Logistic regression was performed to assess for predictors of receiving chemotherapy. The Kaplan-Meier method was used to assess overall survival (OS) and Cox regression analysis was used to assess the impact of covariates on OS.

Results: There were 7,580 patients with MBC of which 417 (5.5%) presented with metastatic disease. Median age was 65 years (interquartile range (IQR) 54-76) and median follow up for living patients was 48 months (IQR 31-77). One hundred and fifty-six (37.4%) patients received chemotherapy. On multivariable logistic regression analyses, treatment at an academic facility was associated with an increased likelihood of receiving chemotherapy (OR 3.14, 95% CI 1.95-5.03, p<0.001) while age ≥65 years (OR 0.54, 95% CI 0.34-0.86, p=0.009) and receipt of hormonal therapy (OR 0.35, 95% CI 0.15-0.85, p=0.021) were associated with a decreased likelihood of receiving chemotherapy. On multivariable Cox regression analysis, higher Charlson-Deyo score (hazard ratio (HR) 1.35-1.78, p<0.05) was associated with worse survival while receipt of chemotherapy (HR 0.76, 95% CI 0.59-0.99, p=0.041) and having insurance (HR 0.34-0.47, p<0.05) were associated with improved survival. Patients who received chemotherapy had improved median (twelve versus eight months), one-year (51% versus 38%), and two-year (35% versus 21%) OS, as compared to those who did not receive chemotherapy (p=0.006).  Conclusions: In this study of MBC patients, there was a survival benefit with palliative chemotherapy in the setting of metastatic disease. As expected, treatment was most often given to younger patients.