AbstractBackground/Objectives: Cancer is most frequently diagnosed in adults over the age of 65 years in the United States (U.S.) Access to cancer care is unequal and the anticipated insufficient supply of oncology physicians may further worsen access to services. The growth of older adults with the corresponding increase in cancer prevalence necessitates the need to characterize Nurse Practitioner (NP) and Physician Assistant (PA) oncology workforce. Design: In this observational, cross-sectional analysis, we examined all ambulatory care malignancy claims from the 2013 Surveillance, Epidemiology, and End Results (SEER) registry linked with Medicare. We identified Fee-for-service Medicare recipients over age 65 years with a cancer diagnosis who received ambulatory care and the providers who cared for them, as identified by the taxonomy codes associated with their National Provider Identifier number. Results: An analysis of over 7 million claims yielded 2.5 million claims for malignancy-specific care. Of the 15,227 cancer providers identified, 32% were NPs (4,806), 28% were double boarded hematology/oncology physicians (4,222), 24% were PAs (3,767), 11% were singled boarded medical oncologists (661), 2.6% were gynecology oncologists (403) and 2.4% were single boarded hematologists (368). Compared to physicians, NPs and PAs were more likely to provide care to rural patients (OR 1.84, 95% CI 1.65-2.05 and OR 1.57, 95% CI 1.40-1.77, respectively). Patients who received NP care were more likely to be female, and reside in high poverty areas. Evaluation of NP care vs. no NP care revealed that NPs were more likely to see female patients (56% vs. 48%, p=.0001) and those who resided in high poverty areas (21% vs. 18%, p=.05). Conclusions: Our study identified a large number of previously unrecognized NPs and PAs providing cancer care to older adults, especially in the Southern U.S., in rural settings and for poorer older adults