The Beverly Hills, 90210 star -- who was first diagnosed with the disease in 2015 -- revealed in 2017 that her cancer was in remission. However, in an interview that aired on Good Morning America on Tuesday, Doherty shared that her cancer had returned, and was in stage four.
The actress admitted to being "petrified" and "pretty scared" of the health battle ahead of her, but said she still wants to "make an impact."
In a new interview with ET, Dr. Kristi Funk -- a breast cancer surgeon, author of the best-seller Breasts: The Owner’s Manual, and women’s health warrior at https://pinklotus.com -- explains what a stage 4 breast cancer diagnosis really means, and offers her advice to women on how to look out for their own health. Funk is not treating Doherty.
As Funk describes, a stage 4 cancer is one that has spread from its original area into other organs.
"Stage 4 breast cancers have cells that have escaped both the breast tissue and the armpit lymph nodes and have landed in a distant organ, so specifically lung, liver, brain and bone," she says. "So, basically these cells have escaped where they initially came from and they take root in another organ and then eventually, unfortunately, they shut down the function of that organ, which is critical to life. So it doesn't matter how big a tumor is in your breast -- you don't need a breast to survive, but that's not true of your liver. So that's why, once you're stage 4 -- except with extremely rare exceptions -- it's an incurable stage."
Funk says that almost a third of breast cancers eventually reach stage 4, and that statistics on survival rates are hard to pinpoint because new treatments are "coming along it seems every six months or so."
Life expectancy, however, varies on where the cancer has spread. "The longest duration after being diagnosed stage 4 comes from having it metastasized only to bone, and the less spots, the better," she says. "Once you hit solid organs -- lung, liver and brain -- life expectancy is less than bone."
"Thankfully, there seems to be almost an endless number of options available to help extend life and make life more comfortable and keep disease progression at bay," she shares.
"Basically we are learning with science to target the mechanisms that cancer cells use to divide and multiply and spread. So if you can throw a wrench in that mechanism, it may disable the cell permanently or at least temporarily, so that's what those drugs are meant to do," she offers.
"It is impossible to prevent it, but you can maximally reduce your risks of ever getting it," Funk says of breast cancer. She recommends that teenage women start self-breast exams one week after their period, and once women reach their 20s, they should continue self-breast exams once a month, as well as receive a clinical breast exam from their gynecologist every three years.
"Then once you hit your 40s, same story: monthly self-breast exam, but your clinical breast exam with the gynecologist moves to annual," Funk advises. "And then starting at age 40, I side with the American Society of Breast Surgeons and recommend that you get mammograms beginning at age 40 and get them once a year, every year and don't stop and don't skip a year until you think you're probably going to die in the next five to 10 years."
As for Doherty and others with a stage 4 breast cancer diagnosis, Funk says that while there isn't a cure, focusing on "relationships and friends and love" can prolong patients' lives.
"I would pay attention to matters of the heart," she says.
Reporting by Leanne Aguilera.
See more on Doherty's diagnosis in the video below.