'Growing Pains' Star Joanna Kerns Reveals She Underwent a Mastectomy — 1 Week Before Alan Thicke's Death

Joanna Kerns has undergone a nipple-sparing double mastectomy after learning of her breast cancer diagnosis and has been “given an all clear — the best of the results I could have had.”

The actress, 64, reveals to PEOPLE exclusively that she was diagnosed with ductal carcinoma in situ — a non-invasive, stage zero cancer trapped inside the milk ducts— in November after a routine Contrast Enhanced Spectrum Mammography screening, which is suggested for women with dense breasts.

After two lumpectomies, Kerns decided to have a double mastectomy in December “instead of risking radiation and the chance of it coming back.”

“Had I not caught my cancer this early on, I would have had to have a year of chemotherapy, and because of the reoccurrence and aggressiveness of this particular type of cancer, which was non-invasive HER2, I chose to do the mastectomy,” she says.

Kerns says the diagnosis was jarring because she has no family history of breast cancer — a disease she thought to be genetic — and felt no symptoms.

“What was really interesting about this process is that breast cancer does not run in my family,” she continues. “I had been vigilant about screenings and exams, except this time I had missed a couple of years in there due to work and family issues, and suddenly I turn around, and it’s two years later, and I hadn’t done it and I have cancer — it was quite shocking.”

But her breast cancer surgeon Kristi Funk — noted for her treatment of celebrities Angelina Jolie and Sheryl Crow — of the Pink Lotus Breast Center tells PEOPLE, “for the most part, breast cancer is not genetic,” adding, “We consider family history and gene mutations, but she didn’t have those issues.”

“It is under our control and has to do with lifestyle choices, which we can absolutely control,” she says. “If all women would control these things to her best ability, we could absolutely eradicate 50 to 90 percent of all breast cancer.”

In an effort to guide Kerns on the path to recovery, Funk suggested she follow a “whole-food, plant-based diet,” which she details in her book called Breasts: The Owner’s Manual: Every Woman’s Guide to Reducing Cancer Risk, Making Treatment Choices, and Optimizing Outcomes (available for pre-order now and on shelves May 1).

“I strongly advise a whole-food, plant-based diet,” she says. “It’s very clear that all animal-based products – whether it’s red meat, white meat, fish, dairy or eggs – cause oxidative stress in your body, which contributes to the imbalance, which leads to inflammation and free radicals and cell damage. Avoiding animal products as much as possible puts you into this super healthy antioxidant environment that cells love.”

Kerns, who is married to architect Marc Appleton, played Maggie Seaver — the loving wife to Alan Thicke‘s Jason Seaver — on ABC’s beloved sitcom Growing Pains from 1985 to 1992. Sadly, just one week after Kern’s mastectomy, Thicke died from a heart attack.

“It was so devastating,” she says. “It was just a very, very hard time. I did go to the memorial four weeks out, and I was very happy to see my whole cast and my producers and dear friends.”

On Thursday night, Kerns stood by Funk’s side as she was honored at at the Yo San University of Traditional Chinese Medicine Gala celebrating Pioneers in Women’s Health at the Bel Air Bay Club in Santa Monica, California.

“I have to thank my husband,” she says. “He was 100 percent behind me, and we have been through a lot together. I think we knew I was in the right place, so that’s 90 percent of it – having the right doctors. I had my husband, I had a plan and I had a great understanding of what it was going to be like. I don’t think I knew the mastectomy was going to be as tough as it was, but I just knew I was going to get better – I knew it because I caught it early.”

“Today, I take care of myself and I’m vigilant – and I’m working out!” she adds. “We went to Scotland and I played golf for nine days.”