Best Friend, Indeed! Shannen Doherty Says Her Dog Detected Her Cancer First

iShannen Doherty tells ET about how her dog Bowie detected her cancer.

The Beverly Hills 90210 and Charmed star reveals that her dog, Bowie, first detected her cancer. "she's become just this crazy protective dog," Doherty told ET.

Actress Shannen Doherty revealed to Entertainment Tonight that her dog, Bowie, first detected her cancer.

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

The Beverly Hills 90210 and Charmed star was first diagnosed with breast cancer in 2015 and has since undergone radiation and chemotherapy treatment and a single mastectomy.

Bowie, a German shepherd, is named after the late musician David Bowie, who lost his 18-month battle with cancer in January 2016 at the age of 69.

Doherty said Bowie's protective instincts have really kicked in since she began treatment: "When I had my first chemo, she would sniff my entire body up and down. And, she was always protective before, but she's become just this crazy protective dog ― it's hard to get close to me when she's around."

The 45-year-old elicited an outpouring of support recently when she shared photos of her getting her head shaved.

Dogs Can Smell a Problem

Dogs are good health monitors because they can smell chemical changes in humans, Alan Beck, director of the Center for the Animal-Human Bond at Purdue University, told LIVESTRONG.COM.

“Smelling chemical changes in the body is really no different than sniffing out drugs or bombs,” Beck said. “Animals can sense changes we can’t even sense in ourselves.”

In fact, dogs can be trained in just three weeks to detect breast and lung cancer up to 97 percent of the time, according to a study published by Integrative Cancer Therapies. Other health conditions pets are being trained to detect are changes in blood glucose levels in diabetics and oncoming epileptic seizures.