Transcript for Shannen Doherty reveals stage 4 breast cancer diagnosis, why she’s sharing it now
into the public. The message full of raw honesty. My stage four cancer came back. And that's why I'm here. Reporter: Actress shannen Doherty is fighting for her life. Now revealing her breast cancer has returned and has now spread to her lymph nodes and bones. It's not the news anyone wants to hear, and you've been living with it privately for a year Yes. Reporter: And you wanted to keep it private, why? I've processed it. I've had a year to let this sit and resonate with me. I definitely wasn't prepared to come out with it. Reporter: Because, when you tell people it that you have stage four met static breast cancer, the way people treat you changes. The way people look at you changes. They look the you like you're dead man walking basically, and they need to say their good-byes to you or something. And also work dries up. I enjoy working and working gives me another reason to wake up every morning. It's another reason to, you know, fight to stay alive. Reporter: Shannen is best known for "Beverly hills 90210". Tell me the size and it's yours. Reporter: And "Charmed." She was first diagnosed in 2015, she documented in raw moments like shaving her hair. It's how it's going to affect the people that you love. Reporter: And in 2017, she posted triumphantly that her cancer was in remission. She continued to act throughout her journey, returning to the role that made her famous, Brenda Walsh in the "90210" reboot months after the death of Luke Perry. What was going through your mind at that moment? Because you didn't share this with anyone. Why wasn't it me? It's so weird for me to be diagnosed, and then somebody who was even seemingly healthy to go it was really, like shocking. Reporter: Shooting the reboot, she put on a brave face publicly, but privately, she knew her cancer was back. I thought, when I finally do come out and I would have worked and people would have looked at that and said oh, my god, she can work and other people with stage four can work, too. Reporter: How did you keep it. I had moments of great anxiety where I thought I can't do it. And Brian was the one person who knew, like we got this, kiddo. Reporter: She admits it has been a struggle. Can you tell me how you found that it was returning? I started feeling some very odd aches. I called my oncologist. Reporter: Were you shocked? I think yes and no. In the back of your head you are always suspecting that it's going to happen. But I had also convinced myself that I had beaten it. I was the true warrior. Reporter: You said you slayed cancer on "Good morning, America." The cancer slayer. Yeah. It's a bitter pill to swallow in a lot of ways. I'm not going to lie. I think the first time around I found some really beautiful, positive way to look at it, and I felt very enlightened. This is a much more difficult one to deal with. I'm grappling. I haven't found my path. And my peace. Reporter: But she's treating her cancer like she does everything in her life. She's fighting it. What have your treatments been like? It's basically a chemo pill you take 21 days on. And a blocker to prevent that's the biggest thing with cancer in the bones. It just starts breaking down your bone. Reporter: And standing by her side through it all, her mother and husband. But even so, it's an isolating place. I imagine when you're in this situation, how alone you feel. You do feel alone. There are moments I feel alone and I have the most amazing support system, friends, but sometimes I think oh, my god, I have a headache. I have stage four, you know. And I don't want to be that person. It can be isolating. Because you're just on a completely different scale. Reporter: A bitter dose of perspective. I want to be, you know, the person that does help people. Like hey, I'm so positive and peaceful and do it like I did last time. But I also think what an incredible disservice to everybody else going through this if I put forth something completely false. Like I'm not okay. That's the truth. Reporter: Shannen is also in the middle of an ongoing legal dispute, state farm, after her home was destroyed in the woolsly fire. Walked in the house and it reeked of smoke. I got passed around from claims adjustor to claims adjustor. So I ended up suing state farm. Reporter: She has been forced to pay out of pocket for losses she believes should be paid by her insurance policy and some claims have been unjustly declined. We reached out and they said we empathize with Ms. Dougherty's health issues and wish her a full recovery. We strongly believe we have upheld our commitment to our customer. They say they have paid 1.1 million to clean and repair plaintiff's home and personal property. But nevertheless she claims she is entitled to additional benefits under her policy. She is set to begin in early March. Reporter: You want to own your cancer story. Yeah, I'd rather people hear it from me. I don't want to be a court document. I want it to be real and authentic. I want to control the narrative. Reporter: How do you handle the fear? I don't know. I'm pretty scared. My mom is, you know, a ridiculously strong, courageous human being. So is my husband, but I worry about him. Reporter: Have you decided how you want to live? Are you going to change how you live? I think the thing I want to do the most right now is I want to make an impact. And I want to be remembered R something. Bigger than just me.
This transcript has been automatically generated and may not be 100% accurate.