Background: An oncologist shortage and rising number of breast cancer survivors has created a strained workforce. Care models that incorporate advanced practice providers (APPs) are recommended to meet this rising demand, particularly during survivorship. The objective of this study is to describe the evolving oncology workforce using anti-estrogen prescribing as a surrogate for breast cancer survivorship care. Methods: We used Medicare Part D Public Use Files to identify prescribers of anti-estrogen therapy from 2013 to 2020. We included medications primarily prescribed in the adjuvant setting for estrogen receptor positive breast cancer, including anastrozole, letrozole, exemestane, tamoxifen, raloxifene, fulvestrant, and toremifene. We assessed the volume of physician and APP prescribers and claims by provider type using descriptive statistics and logistic regression. Individual prescribers were included if they had more than 10 claims. Results: The overall number of anti-estrogen claims did not change significantly from 2013 to 2020, with an average of 3,224,361 annually. There was a significant increase in APP prescribers from 7,815 (8.6%) in 2013 to 12,961 (18.3%) in 2020. There was a reduction in physician prescribers by 24,815 (9.7%) over the same period with an overall net decrease of total prescribers of 19,669 (21.7%). The average annual claims per individual prescriber rose from 2013 to 2020 (Physicians: 2013: 37.5 to 2020: 45.2, p < 0.001; APP: 2013: 28.2 to 2020: 37.0, p < 0.001). The percentage of claims attributed to APP prescribers rose substantially from 6.6% in 2013 to 15.5% in 2020. This represents an increase from 220,000 prescriptions in 2013 to over 480,000 in 2020. Conclusions: Our results indicate an ongoing shift in the provider composition responsible for delivering breast cancer survivorship care. Over the time frame analyzed, there was no significant change in number of prescription claims annually, but an overall decrease in providers. Thus, the rise in APP prescribers is not driven by an increased prescribing volume, but rather seems to reflect an evolving surgical oncology workforce. This has significant implications for the future access to and delivery of timely high-quality cancer care.