Background: Patented anti-cancer drugs launch prices have increased in recent years with subsequent increases after launch. Recently, large price increases of generic drugs were at the center of public attention in the United States. Our aim was to assess price changes with time for Medicare part B anti-cancer generic drugs and to understand how drug characteristics and market structure influence price trajectories. Methods: We included all Medicare part B anti-cancer drugs with price reported in both 2006 and 2016. Patent expiration dates were attached using the Medicare Drug Patent Expiration engine and drugs with a patent expiration date later than 2006 were excluded. Generic manufacturers' FDA approvals for each drug were extracted from the FDA Orange Book. For each drug we extracted the Average Sales Price (ASP) history from October 2006 to October 2016, published by the Center for Medicare and Medicaid services (CMS). Prices were adjusted for inflation, using information obtained from the United States Department of Labor. For each drug we calculated the cumulative ASP change during the follow-up period. Data were analyzed using IBM SPSS Statistics software. Results: We identified 31 anti-cancer generic drugs that met the inclusion and exclusion criteria. During the follow-up period, 15 (48%) drugs had increases in price (median 139%, range 18-2632%). Seven (23%) drugs increased by more than 200% (Table 1). Both gradual price and acute price increases were observed. Some of the drugs which had substantial price increases had no market competition market. Conclusions: Generic drug prices may change substantially with time. Gradual or rapid price increases may be due to lack of generic drug competition, substitution shortages or marketing reasons. New regulations may be needed to prevent further increases in generic drug costs, while balancing the need to maintain financial incentives for drug production and competition.