I’m a nurse, so when I started experiencing pain and swelling in my lower abdomen, I suspected inflammatory bowel disease, or even worse, colon cancer.

But I soon learned my symptoms were caused by non-Hodgkin lymphoma, a type of blood cancer that develops in the white blood cells. Lymphoma causes these cells, called lymphocytes, to grow out of control and crowd out the red blood cells that carry oxygen throughout the body, and...