Actress Loni Anderson died from a rare form of cancer

[Ali Gator]

When actress Loni Anderson died three weeks ago, just two days before her 80th birthday, her longtime publicist said she died from a 'prolonged illness', but gave no further details. Now her death certificate has been made public, and reveals the actress died from metastatic uterine leiomyosarcoma ... a rare cancer that often starts in the uterus and can spread to other parts of the body. It is an extremely rare form of cancer. No other contributing factors were listed.

Leiomyosarcoma is a rare type of cancer that can develop in smooth muscle tissue areas like the digestive system, blood vessels, and uterus, according to the Mayo Clinic. Symptoms can include weight loss, nausea, vomiting, pain, and swelling under the skin. Uterine leiomyosarcomas only have an annual incidence of 0.35-0.64 per 100,000 women — less than 0.001%, according to research in the National Library of Medicine.

Anderson's remains were cremated and buried in Hollywood on Aug. 7.

TMZ was the first to release the death certificate this weekend.