Catherine O'Hara's death certificate reveals rectal cancer diagnosis. What to know.

Catherine O'Hara died from a pulmonary embolism, but her death certificate also revealed she was diagnosed with rectal cancer.

O'Hara's death certificate was obtained by USA TODAY on Feb. 9. TMZ was first to report the news.

Rectal cancer is a type of cancer that starts in the rectum, which is the last several inches of the large intestine, according to Mayo Clinic.

Since rectal and colon cancers are similar in many ways, they're often referred to together as colorectal cancer. But treatments are quite different, the clinic adds.

Here's what to know about the diagnosis.