DCIS at the Margins: The Microscopic Cancer That Can Mean More Surgery
Partnership note: I work with Perimeter Medical Imaging AI in a paid partnership as a patient advocate.
DCIS (Ductal Carcinoma in Situ) is microscopic. It looks and feels like normal tissue to the naked eye. If this microscopic cancer is discovered at the margins after your surgery, it may mean that you need to return for a re-excision.
Before I started working with Perimeter as a patient advocate and member of their industry advisory board, I didn’t realize that DCIS was a factor in so many re-excisions. Did you know that, compared to invasive breast cancer, DCIS triples the risk of re-excision? (Reference Link)
I certainly didn’t. After learning so much, I realized it was a topic worth writing about.
Prior to my lumpectomy in 2019, I wasn’t thinking about my cancer being microscopic. Its impact on my life certainly hadn’t been microscopic, that’s for sure!
I knew my DCIS was relatively small, and that clean margins were important, but I didn’t realize how challenging it was for my surgeon to remove the cancer he couldn’t see. He was relying on his skill, the wire localization that marked where the DCIS was, and the pre-operative imaging.
And, as I shared in a previous post, he checked my margins while I was still in surgery. It turned out that there was DCIS close to the margin, so he took a little more tissue while I was still in the operating room.
What does "DCIS at the margins" mean?
The margin is the rim of healthy tissue around the cancer your surgeon removes. After surgery, the pathologist inks all six sides of the tissue. Then they look at it under a microscope and measure how close the cancer comes to that ink.
Each side gets its own ink color, so the team knows which side is which. If DCIS reaches one edge, the surgeon can go back for more tissue from that side. (Reference Link)
For DCIS, the standard of care is 2 mm of healthy tissue between the DCIS and the edge. As I wrote in my post on clear margins, that’s about the height of a nickel.
If the DCIS touches the ink, the margin is positive. If it sits closer than 2 mm, the margin is close. Either one can mean a re-excision, depending on your unique clinical risk profile.
All of this happens under a microscope at pathology, after surgery is complete.
I remember reading through my pathology report to get to the part that mattered most to me: Did my surgeon get clear margins?
What is DCIS?
DCIS stands for Ductal Carcinoma in Situ. It is a type of breast cancer that forms in the breast ducts but has not yet spread outside the ducts. The abnormal cells are in situ, meaning in place. If they spread into the tissue outside the ducts, the cancer would be called Invasive Ductal Carcinoma, or IDC.
Breast ducts are the tubes that can carry breast milk from the lobules to the nipples. They are located throughout the breast and are one of the most common places for breast cancer to develop.
DCIS is often discovered during routine breast screenings. It can show up on imaging as a line, branch, or cluster of calcifications (cellular debris or dead cells) that look like white spots. (Reference Link) The DCIS itself isn’t showing up on the mammogram, because it is microscopic, but the calcifications can serve as a marker to indicate the possible presence of DCIS. For more detailed information, and some helpful images, I’ve included additional links down below.
Breast calcifications can be benign or cancerous, and depending on the pattern and location, a radiologist may order a biopsy to learn more. The biopsy tissue sample is then evaluated by a pathologist who will determine if it is cancer or not. Not all DCIS has calcifications, though. DCIS without them can sit farther out, closer to the edges of the tissue that was removed. (Reference Link)
DCIS is non-invasive breast cancer and is considered Stage Zero, no matter what size it is. It makes up 20 to 25% of new breast cancer diagnoses in the United States. (Reference Link)
Not all DCIS is the Same
DCIS is a heterogeneous (varied) group of cancerous cells. Imagine a crayon box with different colors in it. Each one is a crayon by definition, but each crayon can be a different color, size, hue, and sharpness. You may have a box with only one crayon inside, or you may have a box of 64. And sometimes the crayons aren’t sitting neatly in the box. They’re scattered all over the desk.
Some of the terms used to describe DCIS on a pathology report include: (Reference Link)
Grade: Low (1), Intermediate (2), High (3). This describes how different the cancer cells look from normal cells. Low-grade cells look closer to normal. High-grade cells look very different.
Type: This describes the patterns of growth of the DCIS. It is possible to have multiple types in one DCIS lesion. These can include cribriform, micropapillary, papillary, solid, flat or clinging, and comedo. Type matters for margins, because some types show up on a mammogram much less than others. (Reference Link)
Necrosis: The amount of dead cells inside the DCIS. It will be noted on the report as present or not present, and then whether there are small pinpoints of necrosis (focal) or a larger area (comedo).
Margins: How far the DCIS is from the closest edge, measured in millimeters, and which edge it is.
Why is there DCIS at the margins?
So, why is DCIS so sneaky? Why is it the reason for so many re-excisions?
- DCIS is microscopic. It looks the same as normal tissue to the naked eye.
- There is no lump since the disease is contained within the duct. Surgeons rely on localizing techniques, pre-operative imaging, and skill to remove the DCIS.
- DCIS doesn’t form distinct edges as it is developing. Unlike other cancers that form a more solid lump, DCIS can spread out in the ducts. The researchers behind the JAMA Surgery study named this as a reason for the higher reoperation rate: the edges of DCIS are less well defined than invasive cancer. (Reference Link)
- DCIS may be underestimated in pre-operative imaging. Certain types of DCIS don’t show up as well in mammography. One pathology review noted that certain types of DCIS, like micropapillary and cribriform, are more commonly underestimated, by about 50% in some cases. (Reference Link)
- DCIS may be present along with the invasive tumor. (Reference Link) If it is along the margins, that may mean an additional surgery to get clear margins.
Microscopic cancer discovered along the margins often means another surgery. Another delay. Another reason we need to wait to complete treatment.
Checking for DCIS at the margins during surgery
Not every surgeon has a way to check for microscopic cancer along the margins during surgery. Since my lumpectomy in 2019, the technologies have continued to advance.
One of the reasons I’m excited about partnering with Perimeter is because they have developed a device called Claire that can be used to visualize DCIS and IDC during breast conserving surgery.
Here’s how Claire fits into surgery. Your surgeon removes the tissue from your breast, and that tissue is then scanned on all six sides with OCT, which stands for optical coherence tomography. OCT is like an ultrasound, but instead of sound waves it uses light. It’s designed to see through the entire 2 mm margin, which as we talked about is the standard of care for DCIS.
Claire’s AI then identifies and marks areas for your surgeon to review. Your surgeon can look at those marked areas while you’re still in the operating room under anesthesia, and take additional tissue if it’s needed.
Claire is an adjunctive tool, which means it supports your surgeon’s own evaluation rather than replacing it. Claire’s AI doesn’t diagnose a margin as positive or negative. Claire is designed as a human-AI team, where the AI acts as a screening tool and your surgeon provides the clinical judgment and makes the call.
Pathology remains the gold standard. You can read more about Claire in my post on clear margins.
Talking with your surgeon about margins
I didn’t know all the questions I could ask before my lumpectomy, especially about margins.
One question I think is important to ask, especially if you are a DCIS patient, is: “What tools do you use to evaluate the tissue margins in the operating room?”
I’ve worked with Perimeter to put together a list of questions you can take with you to your next appointment. Feel free to head over there and get a copy for yourself.
DCIS along the margins: one more reason I keep saying,
“Stage Zero doesn’t mean Zero Challenges.”
Disclosures
This post is produced in partnership with Perimeter Medical Imaging AI. You can read more about my policies here.
The content in this post is general education and information and is not to be considered medical advice. Always talk with your medical team about your care.
The Claire OCT System is an adjunctive tool; it does not replace standard tissue histopathology nor provide a diagnosis. For regulatory and important safety information about Claire, please visit https://perimetermed.com/claire-disclosures/.
References
- DCIS and Reoperation: Langhans L, Jensen M, Talman MM, Vejborg I, Kroman N, Tvedskov TF. Reoperation Rates in Ductal Carcinoma In Situ vs Invasive Breast Cancer After Wire-Guided Breast-Conserving Surgery. JAMA Surgery. 2017;152(4):378–384. https://doi.org/10.1001/jamasurg.2016.4751
- DCIS Diagnoses: National Breast Cancer Foundation. Ductal Carcinoma In Situ (DCIS). Medically reviewed January 31, 2026. https://www.nationalbreastcancer.org/dcis
- DCIS Pathology: Tozbikian G. DCIS. PathologyOutlines.com website. Accessed October 1, 2026. https://www.pathologyoutlines.com/topic/breastmalignantdcis.html
- DCIS Specimen Evaluation: Pinder SE. Ductal carcinoma in situ (DCIS): pathological features, differential diagnosis, prognostic factors and specimen evaluation. Modern Pathology. 2010;23:S8–S13. https://doi.org/10.1038/modpathol.2010.40
- DCIS Imaging: Shehata M, Grimm L, Ballantyne N, Lourenco A, Demello LR, Kilgore MR, Rahbar H. Ductal Carcinoma in Situ: Current Concepts in Biology, Imaging, and Treatment. Journal of Breast Imaging. 2019;1(3):166–176. https://doi.org/10.1093/jbi/wbz039
- DCIS to IDC: Wang, J., Li, B., Luo, M. et al. Progression from ductal carcinoma in situ to invasive breast cancer: molecular features and clinical significance. Sig Transduct Target Ther 9, 83 (2024). https://doi.org/10.1038/s41392-024-01779-3
- DCIS: Understanding Your Pathology Report: https://www.mypathologyreport.ca/diagnosis-library/breast-ductal-carcinoma-in-situ/
- Information about DCIS: https://breastcancernow.org/about-breast-cancer/diagnosis/types-of-breast-cancer/ductal-carcinoma-in-situ-dcis
Jennifer Douglas
Jennifer Douglas is an author, patient advocate, and DCIS breast cancer survivor. After navigating her own breast cancer journey in 2019, she began writing and encouraging others who were newly diagnosed. Her resources include her book, "A Breast Cancer Journey: Living It One Step at a Time," and her online support course, "Encourage: Breast Cancer and Beyond." Jennifer also actively supports patients through her online presence and direct involvement in communities and support groups, offering guidance and encouragement every step of the way.
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