When women undergo lumpectomies to remove breast cancer, doctors try to remove all the cancerous tissue while conserving as much of the healthy breast tissue as possible.

But currently there’s no reliable way to determine during surgery whether the excised tissue is completely cancer–free at its margins — the proof that doctors need to be confident that they removed all of the tumor. It can take several days for pathologists using conventional methods to process and analyze the tissue.

That’s why between 20 and 40 percent of women have to undergo second, third or even fourth breast–conserving surgeries to remove cancerous cells that were missed during the initial procedure, according to studies.

A new microscope invented by a team of University of Washington mechanical engineers and pathologists could help solve this, and other, problems. It can rapidly and non–destructively image the margins of large fresh tissue specimens with the same level of detail as traditional pathology – in no more than 30 minutes.

“Surgeons are sort of flying blind during these breast–conserving surgeries,” said mechanical engineering professor Jonathan Liu. “Oftentimes they’ve left some tumor behind which they don’t know about until a few days later when the pathologist finds it.”

“If we can rapidly image the entire surface or margin of the excised tissue during the procedure, we can tell them if they still have tumor left in the body or not. And that would be a huge benefit to cancer patients,” Liu said. The new light–sheet microscope – which is described in a new paper published June 26 in the journal Nature Biomedical Engineering – offers other advantages over existing processes and microscope technologies. It conserves valuable tissue for genetic testing and diagnosis, quickly and accurately images the irregular surfaces of large clinical specimens, and allows pathologists to zoom in and “see” biopsy samples in three dimensions.

“The tools we use in pathology have changed little over the past century,” said co–author Nicholas Reder, chief resident and clinical research fellow in UW Medicine’s Department of Pathology. “This light–sheet microscope represents a major advance for pathology and cancer patients, allowing us to examine tissue in minutes rather than days and to view it in three dimensions instead of two – which will ultimately lead to improved clinical care.”

Current pathology techniques involve processing and staining tissue samples, embedding them in wax blocks, slicing them thinly, mounting them on slides, staining them, and then viewing these two–dimensional tissue sections with traditional microscopes – a process that can take days to yield results.

Another technique to provide real–time information during surgeries involves freezing and slicing the tissue for quick viewing. But the quality of those images is inconsistent, and certain fatty tissues, such as those from the breast, do not freeze well enough to reliably use the technique.

By contrast, the UW open–top light–sheet microscope uses a sheet of light to optically “slice” through and image a tissue sample without destroying any of it. All of the tissue is conserved for potential downstream molecular testing, which can yield additional valuable information about the nature of the cancer and lead to more effective treatment decisions.