The cancer that has struck Alex Trebek, the 78-year-old host of the television quiz show “Jeopardy!,” is uncommon and devastating: a Stage 4 malignancy of the pancreas, the insulin-producing organ that lies behind the stomach.

Pancreatic cancer strikes about 55,000 people each year in the United States, accounting for 3 percent of all cancers but 7 percent of all cancer deaths. That’s because it can be so difficult to detect and treat. Stage 4, unfortunately, is the most advanced level.

The main risk factor is aging, and Mr. Trebek is “in the right age range,” said Dr. Ursina Teitelbaum, clinical director of the Pancreatic Cancer Research Center at the University of Pennsylvania.

What is pancreatic cancer?

There are several types, but the most common by far is adenocarcinoma: Tumors arise in pancreatic glands that make enzymes to help digest foods.