Background: Drug cost increases are key contributors to cancer care spending in the US. These increases often outpace consumer price index (CPI) inflation, and impact patient access, outcomes, and cost sharing. We analyzed pricing trends and impacts of lower cost generic or biosimilar alternative (LCA) drug launches for key cancer drugs. Methods: Using Medicare Part B drug (Part B) administration & Part D drug (Part D) dispense data for 15 practices in The US Oncology Network, we obtained the unit cost to Medicare for top 30 drugs by total spend over a 6-year period (July 2016 – June 2022). Evaluating cost change patterns in Part B and Part D, we compared trends before and after LCA launches. Results: Over a 6-year period, mean drug costs increased by 12.3% (range: -41.8% to 39%) for Part B and 46.2% (range: -67.5% to 278.2%) for Part D. The largest increases were for Protein-bound Paclitaxel (Part B) (39%) and Ibrutinib (Part D) (278.2%). Many increases exceeded CPI inflation (23.2%) over the same period. Part B/Part D drugs with LCA launches had decreases of -11%/-39%. Non-LCA Part B/Part D drugs increased 21%/ 67%. Prior to LCA launches, Part B/Part D LCA drugs had a mean increase of 22%. After LCA launches, a mean decrease of 36% was observed. Conclusions: Part D drugs have 3.75 times higher increases versus Part B and often outpace CPI inflation. LCAs for branded drugs bend cost increase trends. The impacts of evergreening drug patents and potential shifting of drug coverage from Part B to Part D on costs are ripe for evaluation. The inflation-based rebate and Part D coverage changes in the Inflation Reduction Act (IRA) need to be monitored for its impact on cancer drug cost trends, access, affordability, and financial toxicity for patients.