By Rebecca Pocklington & Claire Rutter

The former Beverly HIlls, 90210 actress was diagnosed with breast cancer in February last year, and she revealed this week it has now been detected in her lymph nodes too in a heartbreaking admission.

But shockingly, she also claims it was her dog Bowie who first detected she was ill.

The german shepherd began sniffing around the area where her tumour was located repeatedly, and it only began to make sense once she had been diagnosed.

"When I got back from surgery, [Bowie] again was kind of right in this area.

"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."

Dogs were previously found to have 98% reliability rate in sniffing out prostate cancer in men, according to research.

The research involved two trained German shepherds sniffing the urine of 900 men - 360 of them had prostate cancer and 540 didn't.

One of the dogs was right in 98.7% of the time while the other was right 97.6% of the time.

The study was carried out by the Department of Urology at the Humanitas Clinical and Research Centre in Milan

Meanwhile, Shannen spoke out in the tell-all chat about the devastating last few months as she bravely battles the disease.

She said: "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.

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

The 45-year-old actress - who had a single mastectomy in May - admitted she is worried about the future because so much is "unknown".

She said: "The unknown is always the scariest part. 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?

"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."

Shannen recently shaved off her long dark hair as her chemotherapy treatment was causing it to fall out, which was "driving her crazy".

"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 mom crying, like, 'My hair, my hair, my hair, my hair.'

"It was just shedding and it was driving me crazy. It was just clumps, and I was like, 'Just grab the kitchen scissors.' And my mom's like, 'Wait, wait, wait.' I'm just, like, 'Grab it.' 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 stages. We did a pixie. And then we did a mohawk, which was my favourite look. And then finally, we had to get the shaver thing and just buzz it off."

Shannen's husband, Kurt Iswarienko, wasn't able to be with her while she had her head shaved, but his response made her "feel better" about losing her hair.

She recalled: "He was in Mexico working and he was texting nonstop in the middle of his photoshoot like, 'Give me pictures, and are you ok? I wish I could be there.'

"He was so stricken that he wasn't there with me but I sent him pictures and videos and he was like, 'Oh my god. You're hot with no hair.' So you know, everybody kind of made me feel better about it."

The actress admitted her treatment has affected her appearance so she wants to be open about her battle with the disease in the hope it helps others.

She said: "People don't realise that cancer -- yes, it ages you -- but also, you can balloon up from the various meds.

"There are so many different reactions you have and so I just -- I didn't want someone to take a picture of me coming out of the grocery store and be like, 'Oh God, look at her.'

"I wanted to put it out there the way it felt the best for me to put it out there. And also, if I could help one person then it makes me go, 'Oh OK.' It's easier to live with having cancer if I know I'm helping at least one person."