e13063 Background: Breast cancer survivors may develop other primary malignancies due to several factors. However, sociodemographic factors associated with the development of head and neck (HN) and esophageal second primary malignancies (SPMs) following management of primary breast cancer (BC) have not been well studied. This study examined the association between BC patients’ sociodemographic characteristics and the development of an esophageal or HN SPM. Methods: Patients ( n= 505,641) diagnosed with breast cancer between 1973 and 2013 in the Surveillance, Epidemiology, and End Results (SEER) 9 program were used for this analysis. HN SPMs included oral cavity, pharynx, larynx, and sinuses. Cox proportional hazards regression was used to evaluate estimators of survival based on age at diagnosis, race, marital status, treatment type, and year of diagnosis. Results: A total of 284 BC patients developed an esophageal SPM, and 969 developed HN SPM. In the adjusted model, increased age at BC diagnosis was a significant predictor for developing both HN and esophageal SPMs. For every 1-year increase in age at diagnosis, the hazard of developing an esophageal SPM increased (HR: 1.05; 95% CI: 1.04-1.06) and HN SPM increased (HR: 1.02; 95% CI: 1.02 -1.03). Hispanic women had a decreased hazard (HR: 0.63; 95% CI: 0.47-0.85) of developing HN SPM compared to non-Hispanic White women, however there was no significant difference for esophageal SPM. Women that were married had a decreased hazard (HR: 0.70; 95% CI: 0.55-0.90) of developing esophageal SPM compared to unmarried women. Conclusions: Sociodemographic factors may be important in the development of SPMs after treatment for breast cancer. While older women with BC were more likely to develop SPMs of the HN and esophagus, Hispanic breast cancer survivors and married women were less likely to develop SPMs of the HN and esophagus. To optimize survival benefits in the breast cancer population, there is need to further explore these sociodemographic factors associated with developing SPMs.