When cancer is surgically removed, the aim is to eliminate all cancerous cells while preserving as much healthy tissue as possible. This involves excising the tumor along with a surrounding border of seemingly normal tissue, known as the surgical margin. This margin is then meticulously examined to determine if any cancer cells are present at its edges.
Defining Positive Margins
“Positive margins” in cancer surgery refer to the finding of cancer cells at the edge of the tissue that was removed. This means the tumor extends to the inked boundary, suggesting cancer cells may have been left behind.
Conversely, “negative margins” or “clear margins” mean that no cancer cells are found at the edge of the removed tissue, indicating a border of healthy tissue surrounding the tumor. While there is no universal standard for how wide a clear margin must be, a common guideline for some cancers, like breast cancer, suggests a margin of 2 millimeters, although some practitioners may consider 1 millimeter or less sufficient. Clear margins generally suggest a lower risk of local recurrence and are the desired outcome of cancer surgery.
The Identification Process
After surgical removal, the excised tissue is sent to a pathologist for microscopic examination, a process that typically takes several days to complete. The pathologist first inks the outer edges of the tissue specimen with different colors to mark its orientation.
The inked specimen is then sliced into thin sections, placed onto microscopic slides and stained. Under a microscope, the pathologist examines these sections to determine the presence or absence of cancer cells at the inked edges and measures the distance between the tumor and the margin.
Factors Contributing to Positive Margins
Despite a surgeon’s best efforts, positive margins can occur due to several complex factors. The inherent nature of the tumor itself plays a significant role, including its size, its specific location within the body, and how invasively it has grown into surrounding tissues. Tumors that have diffuse spread, microscopic tendrils, or are in close proximity to vital structures can make achieving clear margins challenging.
Pre-operative imaging techniques, while valuable, have limitations in precisely defining the microscopic boundaries of a tumor. Cancer cells are not visible to the naked eye during surgery, meaning that even experienced surgeons cannot always visually or by touch detect all cancerous tissue. Certain cancer types, such as ductal carcinoma in situ (DCIS) and multifocal tumors, have also been associated with a higher rate of positive margins.
Subsequent Treatment Strategies
When positive margins are identified after cancer surgery, subsequent treatment strategies are often necessary to reduce the risk of cancer recurrence. One common approach is re-excision surgery, where the surgeon removes additional tissue from the area where the positive margin was found. The goal of this second surgery is to achieve clear margins, confirming that no cancerous cells remain.
Another frequent strategy is radiation therapy, which uses high-energy rays to destroy any remaining cancer cells in the surgical area. For certain cancer types and stages, radiation therapy may be used alone or in combination with re-excision. In some cases, systemic therapies like chemotherapy, hormonal therapy, or targeted therapy may also be considered, depending on the specific type and stage of cancer and the patient’s overall health. The decision for subsequent treatment is highly individualized, made by a multidisciplinary team including oncologists, surgeons, and radiation oncologists, taking into account the unique characteristics of the cancer and the patient’s condition.