PITTSBURGH (AP) — Health insurer Highmark Inc. has sued the University of Pittsburgh Medical Center claiming the hospital network has overbilled it by $300 million for cancer drugs since 2010.

Highmark’s lawsuit, filed late Wednesday, contends UPMC has been charging for chemotherapy treatments administered at doctor’s offices as though they were performed at hospital outpatient clinics. Hospital outpatient clinics charge more for the same treatments.