For those undergoing surgery to remove early-stage breast cancer, one of the most frustrating outcomes is learning, days after the operation, that some of the tumor may have been left behind.
After a typical lumpectomy — the removal of a localized breast tumor — pathologists analyze the removed tissue to see whether its edges, commonly known as the margins, are cancer-free. If not, a second surgery is often suggested.
A new approach may prevent repeat surgeries. Using a fluorescent imaging system, surgeons can see — while still in the operating room — whether cancer cells remain after a tumor is removed. If so, they can remove the residual cancer immediately.
The new technology, known as LumiSystem, was approved by the U.S. Food and Drug Administration in 2024; Stanford Medicine is the first hospital system to integrate it into its breast cancer treatment program. Stanford surgeons Irene Wapnir, MD, Kimberly Stone, MD, and Jacqueline Tsai, MD, have begun using the system on lumpectomy patients who are eligible and choose to receive it.
We spoke with Wapnir, who was also a senior investigator in a pivotal national trial of this technology, about how it works and whom it benefits. This interview has been edited for clarity and length.
Why is it difficult to know whether you’ve removed all of a breast tumor during surgery?
When they perform a lumpectomy, surgeons always try to completely remove a breast tumor. But we can’t always tell where the edges of a tumor are. We need to remove a narrow layer of normal tissue around the tumor while removing as little healthy tissue as possible to preserve the normal appearance of the breast. Thin sections of the tumor are examined under a microscope by a pathologist who determines whether the tissue edges are free of cancer. If not, it could mean that tumor cells were left behind, indicating a need to re-operate. It is important to point out that pathologists examine less than 1% of the surface area of the tumor, so they too can miss tumor cells.
How does this new technology help?
The system lets us look directly inside the breast and inspect the area where the tumor was removed. It uses a fluorescent dye that lights up when it encounters enzymes found only in tumor cells or in tumor-associated inflammatory cells. After removing a tumor, we darken the room and insert a small handheld scope that shows fluorescence in the cavity. The device is connected to a computer that projects onto a screen and guides the surgeon to the cancer cells.
What does this mean for breast cancer patients and their treatment?
What’s most meaningful is that we’re reducing the emotional toll of bringing someone back for another surgery. It’s always very disappointing to have to tell a patient, “We need to go back in.” If we can avoid that, it’s better for the patient and better for the health system.
You were part of a national clinical trial of this approach. What did the results show?
In the study, surgeons used the new system when performing lumpectomies on 357 patients. We found that the technology led to meaningful improvements. Among the 62 patients with positive margins — who would have been recommended to have another surgery — the system identified the remaining cancer in 14.5% of them. In other cases, the system found cancer where the pathologist’s results would have suggested there was no cancer left. That’s powerful. We also saw a high negative predictive value, meaning that if the technology showed no fluorescence, it highly likely was correct.
How does this fit into the surgical workflow? Is it a big change?
Not really. Patients receive the injection of dye about two hours before surgery. After we remove the tumor, it takes just a few minutes to scan the cavity with the imaging device. If needed, we remove additional “shaves” of tissue. On average, the technology added about five to seven minutes to the operation.
Is this now standard for every breast cancer surgery at Stanford?
Not yet. We offer it to eligible patients and explain how it works. Most are enthusiastic about it — once they hear it might avoid a second surgery, they’re on board. We’re careful to be transparent about its limitations. For now, we offer it only to patients with a single breast lesion who haven’t had previous radiation, chemotherapy or lumpectomy. But we’re starting to look at it in patients with recurrences or post-chemotherapy surgeries. I think this kind of technology is helping surgeons, pathologists and patients achieve better outcomes.
