'The Office' star Jenna Fischer underwent treatment for 'aggressive' breast cancer

"The Office" star Jenna Fischer has revealed her battle against an aggressive form of breast cancer.

Fischer, 50, on Tuesday shared an Instagram post detailing her cancer journey, which began 10 months ago with a Stage 1 triple-positive breast cancer diagnosis. The cancer was detected early, before it could be felt, through diagnostic imaging, and Fischer is now "cancer-free" while still taking medications for treatment.

"October is breast cancer awareness month. I never thought I'd be making an announcement like this but here we are. Last December, I was diagnosed with Stage 1 Triple Positive Breast Cancer. After completing surgery, chemotherapy and radiation I am now cancer free," she captioned a photo of herself in her "patchy pixie" phase of growing out her hair.

The actress, who co-hosts the "Office Ladies" podcast with co-star Angela Kinsey, detailed her experience in ensuing slides. She received inconclusive results from a mammogram due to dense breast tissue – which makes it harder to detect cancer in mammograms – and a breast ultrasound and follow-up biopsy confirmed the presence of a tumor in her left breast.

After removing the tumor surgically, she underwent 12 weeks of chemotherapy followed by three weeks of radiation in June.

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Jenna Fischer encourages: 'Don't skip your mammogram'

Fischer's announcement was shared to "implore you to get your annual mammograms. You can also ask your doctor to calculate your Breast Cancer Risk Assessment Score and get any additional screenings required. I'm serious, call your doctor right now."

"My tumor was so small it could not be felt on a physical exam. If I had waited six months longer, things could have been much worse. It could have spread," she added. "Seeing women post photos of their mammogram appointments on Instagram needled me into setting my own (which I was late for). I'm so glad I did. Consider this your kick in the butt to get it done."

"Don't skip your mammogram. Take it from Pam and her Pam Pams," Fischer joked.

What is triple-positive breast cancer?

Triple-positive breast cancer, the diagnosis Fischer received, is estrogen receptor-positive, progesterone receptor-positive and HER2-positive.

After skin cancer, breast cancer is the second most common cancer among women and the second leading cause of cancer-related deaths among American women, according to the National Cancer Institute. Breast cancer rates have risen by 1% each year over the past decade, and women under 50 have seen the biggest increase in occurrences, the American Cancer Society said in a report released last week.

The Affordable Care Act mandates most insurance companies must cover annual screening mammograms for those 40 and older. The U.S. Preventive Services Task Force earlier this year recommended mammogram screenings every other year from ages 40 to 74 for those with an average risk for breast cancer.

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'The Office' co-stars Angela Kinsey, Ellie Kemper show their support

Fischer's friends and "The Office" co-stars sent her well-wishes in the comments under the post.

Kinsey – who played Angela on the NBC comedy – wrote, "I love you and I’m so glad you're sharing. I got your back, always. ❤️"

Ellie Kemper, aka Dunder Mifflin Scranton secretary Erin, commented: "We love you, Jenna ❤️❤️❤️ Thank you for sharing and for inspiring."

Olivia Munn, who opened up about her own breast cancer experience earlier this year, wrote to Fischer, "You already know how much I love you and how incredibly proud of you I am. But I just want to say it again; I love you and by sharing your story you’re helping so many women and saving so many lives. You’re just the best. 💖💖💖💖"

Jennifer Garner chimed in, "Congratulations, @msjennafischer !! I’m so grateful to know you’re on the other side and cancer free! 💗"

Read Jenna Fischer's full statement on her breast cancer diagnosis

"Back in October of 2023 I posted a photo of myself on Instagram preparing for my routine mammogram with a joking reminder to "take care of your ticking time bags" a la Michael Scott. After inconclusive results on that mammogram due to dense breast tissue, my doctor ordered a breast ultrasound. They found something in my left breast. A biopsy was ordered. Then, on December 1, 2023, I learned I had Stage 1 Triple Positive Breast Cancer.

Triple positive breast cancer is an aggressive form of breast cancer but it is also highly responsive to treatment. In January, I had a lumpectomy to remove the tumor. Luckily my cancer was caught early and it hadn't spread into my lymph nodes or throughout the rest of my body, however because of the aggressive nature of triple positive breast cancer it still required chemotherapy and radiation to be sure it didn't return. In February I began 12 rounds of weekly chemotherapy, and in June I started three weeks of radiation. And while I continue to be treated with infusions of Herceptin and a daily dose of Tamoxifen, I'm happy to say I'm feeling great.

I lost my hair during chemotherapy but thanks to some great wigs and hats with hair (which my family affectionately called Wigats) I have been able to wait until now to reveal all that has been going on for me.

I'm making this announcement for a few reasons. One, I'm ready to ditch the wigs. Two, to implore you to get your annual mammograms. You can also ask your doctor to calculate your Breast Cancer Risk Assessment Score and get any additional screenings required. I'm serious, call your doctor right now. My tumor was so small it could not be felt on a physical exam. If I had waited six months longer, things could have been much worse. It could have spread. Seeing women post photos of their mammogram appointments on Instagram needled me into setting my own (which I was late for). I'm so glad I did. Consider this your kick in the butt to get it done.

I'm also sharing in hopes that it will be a source of support to any woman who is going through this right now. As anyone who has had a cancer diagnosis knows, your life changes immediately. It becomes all about doctor appointments, test results, treatments and recovering from treatments. Suddenly everything in your life is geared around one thing: fighting cancer.

It takes a village to fight cancer, and I have had an amazing village.

Until this happened, I don't think I really knew the generosity and kindness that could rain down from one person to another. It started with a team of doctors and nurses. All of them angels.

There were caregivers, some of whom I saw only once, who shared their own breast cancer stories with me. They seemed placed along my path just in the moments when I needed them most. I was connected to other cancer survivors who coached me along the way. Strangers who are now sisters. It reinforced just how powerful sharing can be for the next person taking this journey.

Another big part of the village were my friends and family who have surrounded us with their love and support. Each person had their own special way of caring for us. Some people texted me every week of chemo, some took me for walks, picked up our kids from school, dropped off food, took me wig shopping, some sent prayers in the form of audio messages. Every gesture big or small was felt. All of it was perfect. Also, many people in my life didn't know until very recently. And I needed that too. I needed spaces and people who did not regard me as a cancer patient.

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Breast cancer is the second-most common cancer among women and the second-deadliest type of cancer. In 2023, an estimated 43,170 women died of breast cancer

Thankfully I've been able to keep working during treatments. This was all because I work with my best friend Angela Kinsey who protected me and advocated for me. For a long time, she was the only person in my workspace who knew. When I lost my hair, she wore hats to our work meetings so I wouldn't be the only one.

When I needed a break, we took one. I am so lucky to have a career with this kind of flexibility. Cancer treatment requires a lot of flexibility. For a gal who likes to plan, that was a hard adjustment.

But, continuing to work has brought so much joy to my life during treatment.

People often ask, "How are the kids?" My kids are 10 and 13. My kids are great. We took this journey as a family. They saw that I was able to do many of the same things as before like eating meals with the family and attending their school events. And they saw the limitations cancer treatment had on me like going to bed before they did and needing naps during the day. We told their teachers and coaches and any adults who might be in a position of supporting them. We leaned on our community. They held us up.

We got through it together.

Finally, I need to mention my husband Lee who has been by my side through all of this. And I mean literally by my side... surgeries, chemotherapy, doctor appointments, endless googling, late night ugly cries. He was there for it all. I knew he was a catch when I married him. I was right. After my final chemo and radiation treatments Lee asked me if there was anything I wanted to do to celebrate. I said I simply wanted to ring a bell, with the kids, in our backyard, with everyone throwing confetti. So, we did it.

I'm happy to say that I was recently re-screened, and the treatments worked. I am cancer free. I will continue to be treated and monitored to help me stay that way.

Again, don't skip your mammogram. Take it from Pam and her Pam Pams. Michael was right. Get 'em checked ladies. And know that should you get a breast cancer diagnosis, there is a village waiting to care for you.

That's all for now, Jenna xoxo"