Andrea Mandell

USA TODAY

Shannen Doherty revealed some tough news on Monday, saying her cancer has spread.

"I had breast cancer that spread to the lymph nodes, and from one of my surgeries we discovered that some of the cancer cells might have actually gone out of the lymph nodes," the former Beverly Hills 90210 and Charmed star told Entertainment Tonight. "So for that reason, we are doing chemo, and then after chemo, I'll do radiation."

Doherty, 45, made news recently when she shared photos of herself cutting and shaving her hair. "We did stages," Doherty says now. "We did a pixie. And then we did a mohawk, which was my favorite look. And then finally, we had to get the shaver thing and just buzz it off."

The actress first revealed she was battling breast cancer when she filed a lawsuit last August, claiming her former business managers caused a lapse in her health insurance, delaying her ability to see a doctor. Doherty was ultimately diagnosed in early 2015, and reveals she had a single mastectomy this May. She has since completed three of eight rounds of chemotherapy.

Shannen Doherty shaves head in cancer battle

"The unknown is always the scariest part," she said. "Is the chemo going to work? Is the radiation going to work? You know, am I going to have to go through this again, or am I going to get secondary cancer? Everything else is manageable. Pain is manageable, you know living without a breast is manageable, it's the worry of your future and how your future is going to affect the people that you love."

Her husband, photographer Kurt Iswarienko, whom Doherty married in 2011, has been by her side.

'90210' star Shannen Doherty has breast cancer

After chemo, "I am in bed and it is a rush to the bathroom," she said. "It's, you know, you're throwing up every single second. After my first treatment I lost 10 pounds, instantly. You're throwing up and the last thing you want to do is be in a car. You don't want to be moved, you can't eat. But my husband has to, you know, pick me up. He puts me in the car, he buckles me in, and he drives me to my oncologist and they hook me up to an IV and I get hydrated. ... There's nothing going in my body, it's all going out."

Doherty said she's making her story public so that she can help others.

"People don't realize that cancer — yes, it ages you — but also, you can balloon up from the various meds," she explains. "There are so many different reactions you have and so I just — I didn't want someone to take a picture of me coming out of the grocery store and be like, 'Oh God, look at her.'"

She added: "I wanted to put it out there the way it felt the best for me to put it out there. And also, if I could help one person then it makes me go, 'Oh OK.' It's easier to live with having cancer if I know I'm helping at least one person."