Hogan says the cancer is B-cell non-Hodgkin's lymphoma. He says it may be Stage 4, or at least a very advanced Stage 3.
He spoke at a hastily organized news conference Monday afternoon in Annapolis, surrounded by members of his family and cabinet.
Hogan, a Republican who took office in January, says he's "shocked" by the news.
He says he's been feeling good and has had few symptoms, but has tumors, a low appetite and some pain. Chemotherapy treatment is planned.