Advances in genetic sequencing technology call for changes in how cancer tissue is handled
Genetic sequencing technology is changing the way cancer is diagnosed and treated, but traditional specimen handling methods threaten to slow that progress.
“Deciding how best to obtain (tumor) samples and how best to process them for whole genome or exome sequencing is a pivotal yet unresolved issue with several layers of complexity,” wrote Scripps Clinic physicians Eric Topol, MD, Kelly Bethel, MD, and Laura Goetz, MD, in a recent editorial. “As the new clinical applicability of genomics emerges at a fairly rapid rate, the field of pathology will arrive at a tipping point for a fundamental change in how cancer specimens are handled.”
Currently, tumor tissue obtained through a biopsy is fixed in formalin, a mixture of formaldehyde and water, and then embedded in paraffin for microscopic viewing. However, because the chemical mixture damages DNA, tissue that has been processed this way is difficult, if not impossible, to sequence.
A better alternative is to also routinely freeze a portion of the specimen, which retains the tissue's genetic coding while preserving it for future analysis. In order to have enough tissue to freeze, larger or additional biopsy samples may be required, especially when using minimally invasive needle biopsy procedures.
“We need to completely rethink the way we have collected and stored cancer tissue samples for decades,” said Topol, “It's becoming increasingly clear that obtaining an accurate map of a tumor's DNA can be the key to determining the specific mutations that are driving a person's cancer, how best to treat it and how likely it is to recur.”
Even though complete genetic evaluations of tumors might require higher sample-storage costs and a more invasive biopsy procedure, most patients would likely agree to that option if it translates into a better diagnosis and possible treatment, the authors wrote.
Evidence of such benefit must come from randomized clinical trials that compare detailed genetic evaluation of tumor tissue with the current standard of care for cancer patients, they said.
Patients and their advocates have a direct role to play in this transformation and should raise questions about tumor specimen storage and genetic testing with their doctor, said Topol, who outlines a consumer-led digital health revolution in his book, The Creative Destruction of Medicine.
This column appeared in the Journal of the American Medical Association (JAMA. 2013;309:37-38).