08/04/2012 12:23 am ET Updated Aug 04, 2012

Michelle Rounds Desmoid Tumors: Rosie O'Donnell's Fiancee's Condition, Explained

Michelle Rounds, fiancee of Rosie O'Donnell, is recovering after undergoing surgery for desmoid tumors, according to news reports.

People magazine reported that Rounds had the surgery in June. The couple has decided to postpone their wedding until next summer because of Rounds's illness, O'Donnell wrote on her blog.

"Desmoid tumors, odd and curious beasts, strong and sneaky, a non cancer that acts cancerous," O'Donnell wrote on her blog. "Only 900 cases a year in the US, an orphan disease -- beyond rare, only 3 people per million get this, michelle is one of them."

According to the Desmoid Tumor Research Foundation, desmoid tumors -- also known as aggressive fibromatoses -- are considered benign, but that doesn't mean they aren't dangerous because they grow quickly just like cancer.

The tumors grow in the soft connective tissue in the body, but can also spread to other nearby tissues and organs, the Mayo Clinic reported. They can even grow into bone.

Desmoid tumors are most common in men and in people between the ages of older childhood up until the 40s, according to the American Academy of Orthopaedic Surgeons. Symptoms usually include feeling some sort of lump -- sometimes painful -- in the arm or leg. However, symptoms can become more severe -- limiting mobility -- depending on where the tumors grow.

The location of the tumors could also bring up other health concerns. For example, if the tumors form in the abdomen, it could lead to rectal bleeding or other GI symptoms, according to the Desmoid Tumor Research Foundation.

The tumors are diagnosed with imaging tests like ultrasound, MRI or CT scans, or with a biopsy, according to the Mayo Clinic.

Surgery is usually the best way to remove desmoid tumors, the American Academy of Orthopaedic Surgeons reported, though radiation therapy and drugs (like NSAIDs and Cox II inhibitors) could also help.