'The Office' star Jenna Fischer is sharing more about her triple-positive breast cancer diagnosis. What to know about the disease.

After announcing earlier this month that she was diagnosed late last year with breast cancer but is now cancer-free, actress Jenna Fischer is sharing more about her experience with the disease. Speaking to Hoda Kotb on the Today show, Fischer opened up about losing her hair during her treatment ("I would kind of do a real elaborate comb-over," she said.) and being out on a hike when she got the news that she had cancer.

“I checked the portal on the hike, and that’s when I saw words like ‘invasive,’ ‘ductal,’ ‘carcinoma,’ ‘malignant,’” she told Kotb. “And I was like, ‘Those words sound like cancer words.’”

The Office alum shared on Oct. 8 that she was diagnosed with stage I triple-positive breast cancer on Dec. 1, 2023, and over the past few months, underwent a lumpectomy, chemotherapy and radiation. The 50-year-old chose to keep her illness quiet until she finished treatment but spoke out for Breast Cancer Awareness Month. “I’m making this announcement for two reasons,” Fischer wrote on Instagram. “One, I’m ready to ditch the wigs. Two, to implore you to get your annual mammograms.” She added that “you can also ask your doctor to calculate your Breast Cancer Risk Assessment Score,” calling out the tool that led fellow actress Olivia Munn to be diagnosed with an aggressive form of breast cancer earlier this year.

Here’s what to know about Fischer’s diagnosis and cancer journey.

Fischer was diagnosed with a very early-stage tumor

When Fischer went in for her annual mammogram on Oct. 1, 2023, she posted a selfie with a Michael Scott quote to Instagram. “Gotta take care of those ticking time bags, ladies,” she wrote.

Results from that mammogram came back inconclusive because she had dense breast tissue. About half of women have dense breast tissue, according to the Centers for Disease Control and Prevention, which makes it more difficult for tumors to be identified. "Some women have what we call more 'busy' breasts, where they have more things that, based on mammography alone, make it harder for a screening radiologist to say, 'This is all clear,'" Dr. Lynn Dengel, assistant professor of surgical oncology at the University of Virginia, previously told Yahoo Life. In some cases, these women, including Fischer, have to undergo additional screenings or tests to find out if they have cancer. In Fischer’s case, that meant a biopsy, which resulted in her diagnosis of stage I triple-positive breast cancer two months later.

What is stage I triple-positive breast cancer?

Triple-positive breast cancers are among the more aggressive forms of the disease, but they’re also the most treatable variety, according to MD Anderson Cancer Center. When a tumor is “triple positive,” that means that its growth is fueled by both estrogen and progesterone hormones, as well as a protein called human epidermal growth factor receptor 2 (HER2). About 10% of all breast cancers are triple positive. These three fuel sources allow these tumors to grow more rapidly than others but also provide more treatment targets.

Stage I is the earliest phase at which a cancer is considered invasive, meaning the tumor has grown into surrounding breast tissue, but is still contained to a small area, according to Memorial Sloan Kettering Cancer Center. “Luckily my cancer was caught early and hadn't spread into my lymph nodes or throughout the rest of my body,” Fischer wrote.

How is it treated?

When the disease is at stage I, the main course of treatment, according to the American Cancer Society (ACS), is surgery to remove the tumor and part of the breast where it’s located, a procedure known as a lumpectomy or partial mastectomy. Fischer underwent a lumpectomy but because her cancer was a more aggressive, triple-positive tumor, she was also treated with 12 rounds of chemotherapy and three weeks of radiation “to be sure it didn’t return,” she said. Fischer noted that she lost her hair during chemotherapy and wore hats and wigs with hair — “which my family affectionately called Wigats” — to help her maintain privacy amid her treatment.

Like many women diagnosed with hormone-fueled breast cancers, Fischer is still receiving additional treatment — infusions of Herceptin, a drug that blocks chemical signals that tell HER2 positive cancer cells to grow, and Tamoxifen, which blocks cancer’s ability to use estrogen as fuel — to reduce the risks of her cancer coming back.

Fischer’s prognosis is good

The actress shared that she’s now “cancer-free” and “feeling great” despite her ongoing preventive treatments. The outlook is good for women with stage I cancers, with a 99% five-year survival rate, according to the ACS. But most people diagnosed with hormone-fueled cancer in the disease’s early stages will be on hormone therapies like tamoxifen for several years.

As for now, Fischer’s hair is growing back and she “wanted to post a photo of myself in my patchy pixie looking happy and healthy to go along with this big news,” she wrote.

Her message: 'Consider this your kick in the butt' to get screened

Fischer’s diagnosis came as the result of an annual mammogram. The U.S. Preventive Services Task Force recommends that all women between ages 40 and 74 get mammograms every two years (the ACS says that women should get the screening every year between ages 45 and 54 and “have the option” to start at 40). However, 59% of respondents to a recent survey said they forego their recommended mammograms. Fischer almost skipped hers last year. “Seeing women post photos of their mammogram appointments on Instagram needled me into setting my own,” she wrote. Fischer explained that her tumor was too small to have been caught by a physical exam. “If I had waited six months longer, things could have been so much worse. It could have spread,” she said. “I’m so glad I did. Consider this your kick in the butt to get it done.”

Fischer also urged others to ask their doctors to calculate their breast cancer risk with the assessment tool that Olivia Munn credits with saving her life after it led her to get additional screenings and be diagnosed with an early but aggressive form of the disease. “I’m serious, call your doctor right now” to ask about the tool, urged Fischer. While mammograms are recommended only for women 40 and older, a doctor can use the risk assessment tool with patients as young as 35, who may be more likely to get cancer due to factors like their family history or past illnesses. “Basically, every single woman needs to know their lifetime risk, even if you don't have a family history of breast cancer," Munn's own ob-gyn and the host of the SHE MD podcast, Dr. Thai?s Aliabadi, previously told Yahoo Life.

This article was originally published on Oct. 8, 2024, and has been updated.