The need for clear margins is paramount, in successful breast conserving therapy. What is a margin, and, what constitutes a clear margin has been the topic of conversation/debate for years.
The surgical margin is the distance seen histologically (under the microscope) between the edge of the surgical specimen, and, the cancer within the specimen. This distance is measured, typically in millimeters. When the surgical specimen is removed, it should be oriented by the surgeon, so as to indicate which side of the specimen, corresponds to which location with the surgical cavity in the patient. Typically, there are 6 margins reported. If a margin is too close, it may require re-excision. Re-excision is a second operation, to remove more tissue from an area where the tumor cells were too close, or involving, the edge of the specimen.
Intraoperatively, the margins can be assessed clinically (by touch), radiographically (by performing an x-ray/mammogram/ultrasound of the specimen, to assess how close disease seemed to be to the edge. Recently, a new device, called the Margin Probe, has been used to assess the edges/margins of the surgical specimen. This device uses Radio Frequency (RF) Spectroscopy to determine cellular differences between normal and cancerous tissue. Studies have shown that this device may reduce re-excision rates by as much as 50%. http://www.marginprobe.com/dr-eric-brown/
So, what is the significance of a positive margin? Positive margins (tumor cells seen directly on the edge of the surgical specimen) are associated with a two-fold increase in the risk of local recurrence (IBTR – Ipsilateral Breast Tumor Recurrence) compared with negative margins. There is now a universal consensus (Society of Surgical Oncology and the American Society for Radiation Oncology) that ‘no tumor on ink’ – no tumor to the edge of the surgical specimen, is associated with low rates of IBTR and has the potential to decrease re-excision rates, improve cosmetic outcomes, and, decrease health care costs.