EXCLUSIVE: Shannen Doherty Says Her Dog Was First to Detect Her Breast Cancer

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Before her frightening breast cancer diagnosis, Shannen Doherty received a surprising warning sign.

The former Beverly Hills, 90210 star tells ET that it was actually her beloved dog, Bowie, that first appeared to detect that something was wrong.

"She would obsessively sniff right here on my right side for a long time before," Doherty tells ET's Jennifer Peros. "So, it made sense when I got diagnosed."

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The 45-year-old actress was officially diagnosed with breast cancer in February 2015. Doherty now says that the disease has spread to her lymph nodes.

She has undergone three out of eight rounds of chemotherapy thus far and says she'll do radiation once the chemo has been completed. In May, Doherty underwent a single mastectomy.

"When I got back from surgery, [Bowie] again was kind of right in this area," Doherty says, gesturing towards her right side. "Then when I had my first chemo, she would sniff my entire body up and down. And she was always protective before, but she has become this crazy, protective dog. It's hard to get close to me when she's around."

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Bowie, named after the late music icon David Bowie, even sometimes sports an adorable "Security" shirt while watching out for her famous mom.

Tune in to Entertainment Tonight on Tuesday for more from our exclusive, emotional sit-down with Doherty.

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