A lifesaver with a catch: Powerful new cancer drugs can trigger diabetes — and no one is certain why

The first two rounds of treatment went off without a hitch. But last November, after receiving a third dose of potent immunotherapy for his skin cancer, Rich Lenihan started to feel tired and weak.

He was urinating constantly, and no amount of water could abate his thirst. A blood test revealed glucose levels that were through the roof.

Lenihan, at age 62, had developed a disease akin to type 1 diabetes — formerly called “juvenile” diabetes — a rare complication of drugs known as checkpoint inhibitors that rev up the body’s immune assault on tumor tissue.