Medicare Part D Spending on Drugs Prescribed by Oncologists: Temporal Trends and Regional Variation.

Purpose: Drug cost is a significant factor in the ever-increasing expenditures for cancer health care.

Methods: We used Medicare Part D administrative data to explore prescribing patterns and attributed drug costs of oncologists from 2013 to 2017. We highlighted regional variation in spending and potential associations. We used the location quotient (LQ) to measure the relative concentration of oncologists compared with the national average by hospital referral regions. Costs were reported in 2017 US dollars (inflation adjusted) for cross-year comparisons.

Results: Oncology's share in Part D spending showed an uninterrupted increasing trend. In 2017, oncologists prescribed medicines with $12.8 billion in Part D costs (8.3% of all Part D payments), which exceeded 2013 costs by $7.3 billion, when their claim payments were $5.5 billion (5.0% of all Part D payments). Oncology contributed a higher annual growth in Part D drug costs compared with all other providers (15.1% and 3.1%, respectively, for 2017). The top 3 drugs increased cost by approximately $3.5 billion from 2013 to 2017. Across hospital referral regions, the oncologists' Part D share varied (median in 2017, 7.7%; interquartile range, 6.2%-9.3%) and was higher across regions where oncologists had an LQ significantly > 1 (mostly in areas with centers that excel in cancer care) and lower for an LQ significantly < 1 (median, 9.7% 6.2%, respectively; < .001).

Conclusion: Oncology increased its share in Part D drug spending, disproportionately to all other providers, with regional differences partially moderated by the oncology workforce and quality of cancer care.