Health insurer Cigna will spend about $52 billion to acquire the pharmacy benefits manager Express Scripts, the latest in a string of proposed buyouts and tie-ups in a rapidly shifting landscape for the health services industry.

Including $15 billion in debt, the proposed $67 billion acquisition would follow a deal late last year in which CVS Health Corp. would spend $70 billion for Aetna Inc.

The health sector has been jolted not only by the Affordable Care Act and questions about the form of U.S. health policy going forward, but also the potential arrival of the ultimate disruptor, Amazon.com.

The deal announced Thursday consists of $48.75 in cash and 0.2434 shares of stock of the combined company per Express Scripts share.