Danielle Fishel opens up about breast cancer diagnosis, encouragement and message for others

One in three women are diagnosed with breast cancer each year, according to the American Cancer Society – and Danielle Fishel is one of them.

The director, producer and actress, best known for her role as the spunky teen Topanga on the '90s hit "Boy Meets World," sat down with "Good Morning America" to talk about the cancer diagnosis that changed her world, and to share her journey – including a key message that she considers lifesaving.

"My specific type of cancer was very aggressive. And I was looking healthy, I was feeling healthy. I didn't have any lump. I was just goin' about my life," she said.

The 43-year-old mother of two was diagnosed with DCIS, or ductal carcinoma in situ, which the American Cancer Society describes as a Stage 0 breast cancer because it's a non-invasive or pre-invasive, early-stage breast cancer that occurs when the cells that line the breast milk ducts have turned cancerous but have not yet spread into the nearby breast tissue.

"Having to break the news to my husband was really hard. Both of his parents passed from cancer," Fishel said. "I waited until the kids went to bed and he actually brought it up. He said, 'Still no results yet, huh?' and I said, 'No, I did get the results back and I do have cancer.' And I mean, truly just saw the blood drain from his face."

For the last three months, Fishel has undergone two surgeries, including a lumpectomy, and has weighed her options about treatment plans.

"My recovery is going well, I no longer have cancer," she said. "I do still need to make a decision moving forward about radiation."

Fishel first revealed her diagnosis publicly on her podcast "Pod Meets World," which she co-hosts with her former "Boy Meets World" costars Rider Strong and Will Friedle.

"I hopefully could use my own experience to be able to encourage other people to go and get their regular check-ups," Fishel said when asked why she chose to share her diagnosis. "'Cause had I put mine off, it may not have been Stage 0. It may not have been DCIS. It could've been invasive cancer. And I'm so grateful that I prioritized my health and said, 'I'm gonna go and have this mammogram.' And it changed my life."

Fishel also explained that growing up in the 90s, when "there was so much messaging around people being selfless and how amazing that is," prompted her to ask herself questions about that later in her life.

"As I've gotten older, and I've become a mom and a wife, I started thinking, 'Is being selfless actually the virtue we think it is? Or is it really harming us?'" Fishel explained. "And I think it's really harming us. This idea of putting everybody else before yourself. And when it comes to my health, when it comes to my mental health, those are just two areas I'm not willing to sacrifice for anyone. I'm not willing to be selfless – I'm going to be selfish."

According to the American Cancer Society, about one in five breast cancers will be DCIS, and nearly all women diagnosed with it can be cured.

"I feel like it's a very Topanga thing to be saying to people, 'Hey, your health matters. Your wellness matters. Can you please go have your preventative check-ups?'" Fishel said of her former TV persona.

Now, she's using her platform to encourage others to get their mammograms.

"If you grew up watching me on TV, it’s probably time for you to get a mammogram, so go get one," she said.

Fishel's story, and her critical reminder to not put off getting a cancer screening, is in line with the latest guidance from the U.S. Preventive Services task force, which recommends women with average risk should get a mammogram starting at age 40, with follow ups every two years.