Shannen Doherty reveals her breast cancer has spread.

In an interview with Entertainment Tonight, actress Shannen Doherty has revealed that her breast cancer diagnosis is much worse than first thought.

The actress revealed the devastating news that her cancer may have spread to her lymph nodes.

"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," Doherty tod ET.

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

The actress - who was diagnosed in February last year - also revealed she underwent a single mastectomy in May as part of her treatment.

Despite her gruelling treatment plan, Doherty revealed the scariest part of her diagnosis was not knowing what was going to work.

"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?" she said.

"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 former 90210 star has completed three out of eight rounds of chemotherapy so far, and recently shared her journey of losing her long, brown hair with her fans on Instagram.

"After my second treatment, my hair was really matted, like in dreadlocks. 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 mum crying, like, 'My hair, my hair, my hair, my hair.'

"It was just shedding and it was driving me crazy. She went and grabbed the kitchen scissors, and put it in a ponytail and she just chopped it off. And it was this cute little bob, but it wasn't enough, you know, it was falling out. 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."

Protect yourself by learning how to perform a self-breast check...