Study reveals ways to determine surgical margins for feline tumors

By Veterinary Practice News Editors

Cats with feline injection-site sarcoma (FISS) often have noncancerous tissue removed with their tumors as a precaution. This can have detrimental effects on felines, which is why new research from Oregon State University (OSU) is so promising. The researchers are finding ways to be more precise in determining which tissues are noncancerous.

They do this by analyzing tissue contraction at various stages of the post-operative examination process. Understanding how surgical margin length decreases from surgery to pathology — because of how the removed tissue shrinks and tumor cells invade surrounding tissues — can lead to better surgical margin planning and in turn a better prognosis, said Milan Milovancev, DVM, DACVS-SA, a board-certified veterinary surgeon at OSU’s College of Veterinary Medicine.

“If we can understand the relationship between what the pathologist sees on a slide under a microscope and what the surgeon is taking out in the operating room, and what accounts for the differences between the two, then we can work backward and figure out how much surgical margin to take,” he said.

The pilot study, which looked at 35- to 55-millimeter surgical margins from five cats with FISS, found the greatest margin decreases occurred right after excision. It also found the margins tended to be larger than necessary.

“Older studies showed that if you had bigger margins, cats would live longer,” Milovancev said. “The previous margin guidelines of 2 to 3 centimeters had been found to be inadequate, and the new guidelines were 5, which seemed like a big jump and in some of these cats may cause a lot of unnecessary suffering.

“The net take-home is that yes, 2 to 3 centimeters is indeed inadequate, but we didn’t find any tumors getting close to 5 centimeters. We can reduce morbidity by surgically removing what we need to take out and leaving what doesn’t need to be taken out.”

Milovancev notes that future, larger studies that categorize results by factors that might influence tumor-free margin length — such as tumor grade and location — are likely to lead to more refined preoperative surgical planning.