That is the topic of a recent paper Tyan, Lam and Milligan (2023). Using newly created database from
financial databases combined with press releases, news sources, clinic websites, and financial 10-K reports, the authors found that:
During 2003 to 2022, 724 oncology clinics (53% radiation, 32% medical, 15% multi-oncologic) became affiliated with a PE-backed platform company, constituting 10% of an estimated 6919 oncology clinic locations in the US. At least 2060 oncologists (64% medical, 36% radiation) were affiliated with clinics at the time of initial PE acquisition, constituting an estimated 10% (1318 of 13 531) of practicing medical oncologists and 15% (742 of 4886) of radiation oncologists.
The full paper is here.