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"The 23 percent number is very significant, because it argues that if pathologists just do one section, you may want to ask them to do more," he explained. "We think the information you get by doing more is significant."

According to Cody, 30 years ago the standard of care for breast cancer patients was complete dissection of the axillary lymph nodes (those found under the armpit) followed by cell-shape analysis using a single tissue slice from each node. Such a surgery would typically collect 15 to 20 nodes, on average. Today, however, a different, less traumatic approach called sentinel node biopsy is used.

In sentinel lymph node (SLN) biopsy, a patient's tumor is injected with a combination of dye and radioactive tracer molecules. The following day, only those lymph nodes to which the tracer molecules migrated (the SLNs) are biopsied and analyzed. So, instead of harvesting 15 to 20 nodes, on average only two are three are collected using the new technique.

That reduction in work per node has a real payoff, because pathologists can delve much deeper into each sample, Cody explained.

"Because you remove fewer nodes, you can study them more carefully, and we argue that the information you get by doing that is prognostically significant," he said.

Current guidelines from the College of American Pathologists recommend analyzing one tissue slice per biopsied lymph node, Cody noted. Yet for years, he said, physicians have known that the more carefully one looks, the more cancerous cells one can find. The problem has always been one of balancing the additional work and expense required against the likelihood of success -- some studies have suggested a pathologist would need to analyze as many as 1,600 additional sections to find a single additional node-positive case.