Sitcom star Valerie Harper who rose to fame on “The Mary Tyler Moore Show” died last week following a long battle with a rare cancer called leptomeningeal carcinomatosis. She was 80.

While most patients who receive the diagnosis only live a few months, she lived more than six years with the disease, which occurs when cancer cells spread into the fluid-filled membrane surrounding the brain, known as the meninges.

“This is a rare complication of systemic cancer that occurs when cancer cells that are floating in the bloodstream enter the cerebrospinal fluid (CSF) that surrounds the brain and start to grow there,” said Peter Forsyth, MD, chair of the Department of Neuro-Oncology at Moffitt Cancer Center. “These aren’t solid tumors in the brain but rather are like little seeds spread in the fluid that covers the brain and spinal cord.”

Harper was diagnosed in 2013, just four years after beating lung cancer. While she lived much longer than most patients with leptomeningeal carcinomatosis and even managed to compete in “Dancing With The Stars” in 2014, Forsyth believes it was metastasized from her lung cancer.

“The most common tumors that go into the CSF and cause leptomeningeal disease are cancers in the breast and lung and melanoma,” Forsyth said. “So yes, I would say this is from her lung cancer.”

Harper underwent a successful lung resection procedure in 2009 to remove a tumor found in her lung and was considered cancer free for four years. But in 2013 she noticed changes that concerned her. She experienced something she called “frozen jaw” which she compared to a feeling of Novocain injected during a visit to the dentist. She also had difficulty remembering lines during rehearsals.

“This is a terrible disease where most patients only live a few months,” Forsyth said. “The treatments that exist now aren’t that effective, but we are researching ways in the lab and the clinic to understand this disease so we can find much better ways of treating patients.”

Harper underwent a variety of treatments including chemotherapy, according to her husband, Tony Cacciotti, who documented Harper’s journey on social media.

How Valerie Harper's Husband Tony Cacciotti Was Undyingly Devoted to Her Until the End https://t.co/uNp4Mxi4xV

— People (@people) August 31, 2019

Leptomeningeal carcinomatosis is uncommon, occuring in about 1-5% of patients with cancer. Forsyth said that Moffitt does treat patients with the disease and is currently operating a clinical trial.

“We do a lot of research here in this area and have several grants to understand it better and to develop new treatments,” Forsyth said. “We are among only four or five centers in the country that specializes in the research and treatment of this disease.”

That research involves not only treating the tumor cells but identifying their vulnerabilities and identifying strategies for resistance. Forsyth added that researchers are also looking at treating the CSF environment directly to make it less supportive of tumor cell growth.

“Our early research shows that immunotherapies may help with these treatments and that we may need tumor-specific treatments,” Forsyth said. “Some patients’ CSF environment is a bit too friendly to tumors and may encourage them to grow, while others present as more hostile and can help kill tumor cells.”

Following her breakout role as Rhoda Morgenstern on “The Mary Tyler Moore Show,” Harper went on to star in a spin-off of that series simply called “Rhoda” from 1974-1978. In the 1980s she starred in the sitcom “Valerie’s Family.”

In a 2015 interview with People Magazine, Harper discussed her diagnosis and said that she was prepared for the inevitable.

“I’m ready. I’m ready to go,” Harper said in the interview. “Maybe that’s the secret. I don’t want to, my God, I want to live to be 102, but I am not banking on anything, really, because we shouldn’t. We don’t know what’s around the corner. I think you just take each day and get the best out of it and do what you can and have fun.”