In Health Affairs, Abby Alpert and colleagues evaluate the reasons behind the increase in vertical integration in the market for cancer care. Much of the move towards consolidation over the past decade has been vertical - hospitals acquiring physician practices - instead of horizontal - physician practices or hospitals merging with similar entities. The authors' analysis shows that the rate of hospital or health system ownership of practices doubled from about 30 percent to about 60 percent between 2003 and 2015. The two most commonly cited explanations for this consolidation are a 2005 Medicare Part B payment reform that dramatically reduced reimbursement for chemotherapy drugs, and the expansion of hospital eligibility for the 340B Drug Discount Program under the Affordable Care Act (ACA). The authors evaluated the evidence for these drivers through a difference-in-difference approach assessing whether consolidation increased more in areas with greater exposure to each policy than in areas with less exposure. They find little evidence that either policy contributed to vertical integration, and instead attribute increased consolidation in the market for cancer care to a broader post-ACA trend toward integrated health care systems.