My mother was diagnosed with rheumatoid arthritis that turned out to be ovarian cancer. Have you ever heard of this?

Yes, in a small number of cases cancer can present like arthritis. This is true for quite a few different kinds of cancer. The condition is called a paraneoplastic syndrome. Para means like. Neoplastic is another word for cancer. Syndrome refers to a group of symptoms.

In a recent study, the Mayo clinic in Jacksonville, Florida, reported four cases of hand and arm symptoms that later turned out to be from ovarian cancer. There was a wide range
of symptoms from pain and stiffness to actual contractures. Contractures are fixed positions of the joints so the patient can't fully flex or extend.

Most cases are finally diagnosed properly when the symptoms don't clear up as expected with treatment. Sometimes the cancer gets worse and the patient develops other symptoms to guide the doctor.