Shannen Doherty on her terrifying cancer battle: "I wasn't going to live."

After sharing her emotional battle with breast cancer with her fans on Instagram, Shannen Doherty is now opening up about her health in an interview with Entertainment Tonight.

The former 90210 star was diagnosed in with breast cancer in February last year, and has recently shaved her head as part of treatment.

"I started thinking that I wasn't going to live," she tells ET in a teaser for the interview, due to air in full this week.

"I don't look past today... I want to believe that if I fight, I'm going to be OK".

Speaking of her changing appearance, Doherty also reveals, "I don't know if I'll ever look like me again".

The actress' cancer diagnosis is already a heartbreaking story. She first revealed her diagnosis to the public in a lawsuit filed in mid-2015, which revealed her management had failed to keep her health insurance up to date.

The actress claims she wasn't able to see her doctor for regular check-ups while she was uninsured, and it wasn't until she was able to re-enroll with the Screen Actor's Guild in 2015 that she could seek treatment, by which stage her breast cancer had already progressed.

"Had she been insured and able to visit her doctor, the cancer could potentially have been stopped, thus obviating the need for the future treatment (including mastectomy and chemotherapy) that Plaintiff will likely have to suffer through now," the lawsuit read.