08/02/2016 10:53 EDT | Updated 08/02/2016 10:59 EDT

Shannen Doherty Says Her Breast Cancer May Have Spread

"The unknown is the scariest part."

Amid an on-going battle with breast cancer, Shannen Doherty has revealed the disease may have spread.

In an interview with ET, the "Beverly Hills, 90210" star said she has started chemotherapy.

"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," said Doherty. "So for that reason, we are doing chemo, and then after chemo, I'll do radiation."

The 45-year-old actress also revealed that she had a single mastectomy in May, but admitted that it isn't the treatment itself that's the most difficult part of having cancer.

"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."

The other hard part about having breast cancer? Getting fitted for a new bra.

"It was traumatic and horrible, and I didn't think anything of it at the time, then my mom went with me and I broke down crying in the dressing room and ran out," Doherty said about the experience. "And then sat in the car crying."

Doherty was diagnosed with cancer in February 2015, and since then, she has shared her journey on her Instagram page.

A week ago, she posted pictures showing her in various stages of cutting off her hair while undergoing chemotherapy.

Step 6

A photo posted by ShannenDoherty (@theshando) on

"After my second treatment, my hair was really matted, like in dreadlocks," she wrote. "And I went to try and brush it out, and it just fell out. I just remember holding onto huge clumps of my hair in my hands, and just running to my mom crying, like, 'My hair, my hair, my hair, my hair.'"

She also shared an update on her health via Instagram, thanking her loved ones for supporting her.

"Thank you to these three who helped me thru an impossibly tough day and continue to be there every minute supporting and loving me," she wrote.

According to the Canadian Press, Doherty's cancer was publicly revealed in a lawsuit filed against her former business managers. In the lawsuit, she claims that they mismanaged her money and allowed her health insurance to lapse. As a result, she didn't go to the doctor until she had insurance, thus delaying the cancer diagnosis.

"I started thinking that I wasn’t going to live," Doherty admitted in the ET interview. "I don’t look past today, [and] I don’t know if I’ll ever look like me again. I want to believe that if I fight I’m going to be okay."

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