'Boy Meets World' actress Danielle Fishel has breast cancer. She caught it so early it's at stage 0.

Actress Danielle Fishel has been diagnosed with breast cancer, the Boy Meets World star revealed on her podcast. “I was recently diagnosed with DCIS, which stands for ductal carcinoma in situ, which is a form of breast cancer,” Fishel said on an Aug. 19 episode of Pod Meets World. “It is very early. It’s technically stage zero.”

Fishel credits a reminder message for her early diagnosis. “The only reason I caught this cancer when it is still stage zero is because the day I got my text message that my yearly mammogram came up, I made the appointment,” she said. Fishel explained that she will soon undergo surgery to remove the “micro-invasive” cancer, followed by some additional treatment. “I’m going to be fine,” Fishel said, though she added that she’s had to make “a lot of decisions over the last couple of days.”

She decided to reveal her diagnosis to help others, providing transparency around those difficult initial days — or what she calls the “messy middle.” Though stage zero is the earliest form of breast cancer, experts say that the phase after diagnosis can be stressful, as patients deal with the uncertainty and their treatment options. Here’s what stage zero means and how common it is.

What is stage 0 breast cancer?

It goes by many names, Dr. Kelly Hewitt, an assistant professor of surgical oncology at Vanderbilt University tells Yahoo Life. Along with the technical term DCIS, it’s also sometimes called precancerous or pre-invasive breast cancer. At this stage, “abnormal, malignant cells are confined within the [milk] duct within the breast tissue and haven't invaded through the lining of the duct,” Hewitt says. “These cells can’t really escape or go anywhere, but once they do break through the lining of the duct, that’s when it becomes stage 1 or invasive.”

Still, it’s an anxiety-inducing situation. “Anybody who hears ‘cancer’ and your mind goes to the worst-case scenario,” Hewitt says. “It can be a very challenging discussion and, often, even more challenging than [with] someone with a more advanced cancer, where it’s very straightforward what they need to do.”

Fishel said that her cancer was diagnosed as “micro-invasive,” meaning, according to Hewitt, that cancer cells have broken through the duct lining in a very, very small area of the breast, “on the order of millimeters or less.”

What are the signs and symptoms of DCIS?

At this early stage, most patients don’t have any symptoms, Hewitt says. Typically, DCIS is discovered after a mammogram, which might show calcification, which are calcium deposits in the breast tissue. (Most of the time these calcifications aren’t cancerous, but they can be an early sign of cancer.) From there, doctors will perform a biopsy to test the tissue for cancerous or precancerous changes.

How common is it?

Around one in five new breast cancer diagnoses in the U.S. are stage 0, or DCIS, according to the American Cancer Society. And though it’s the earliest form of the cancer, Hewitt says she sees the diagnosis in patients of all ages. Studies estimate that, on average, women are typically diagnosed in their 50s. Fishel is 43 years old.

How is stage zero breast cancer treated?

For the most part, doctors treat stage zero and stage 1 cancer the same way, Hewitt says. The first step is almost invariably surgery, which Fishel says she plans to undergo. Some women may choose to have a complete or partial mastectomy (also called a lumpectomy) to remove all or part of the breast tissue. The type of surgery depends in part on how big the area affected by cancer is relative to their breast, as well as personal preferences.

After surgery, if all the cancerous tissue has been removed, most patients will undergo radiation. If testing shows that their tumor is fueled by estrogen, patients may be put on an additional medication that suppresses the hormone and induces menopause. After that, “the vast majority of patients are cured, end of story,” Dr. William Gradishar, chief of hematology and oncology and a professor of breast oncology at Northwestern University's Feinberg School of Medicine, tells Yahoo Life. The survival rate for DCIS is 98%, according to the Breast Cancer Research Foundation.

What can be done to reduce your risk?

A family history of breast cancer is one predictor. This is especially true for those who have inherited mutations on the BRCA 1 or BRCA 2 gene, which carries a higher risk of breast cancer. Risk is also elevated for people whose mothers or sisters have been diagnosed with breast cancer. Aside from living a healthy lifestyle — including not smoking, not drinking too much, staying physically active and maintaining a healthy body weight — Hewitt says the best thing you can do is know your familial history and get your mammogram regularly.