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A New HER2 Tool for Pathologists
By Marilynn Larkin
After your breast tumor is biopsied, the pathology lab runs a number of tests on it to get a clearer picture of what kind of cancer you have, the characteristics that make it grow, and its size and location. This, in turn, helps your oncologist evaluate the best treatment for you. One of the characteristics a lab looks for is a tumor’s HER2 status.
Having too many copies of the HER2/neu gene in the breast cell, which overproduces the HER2 protein, can make the tumor grow quickly and aggressively. If your tumor is classified as HER2-positive, it’s likely to respond well to the drugs Herceptin or Tykerb.
Typically, the pathology lab starts by conducting an immunohistochemistry (IHC) test on the tumor tissue sample, which measures the amount of HER2 protein in the gene. If the results are inconclusive, the pathologist will confirm them with a fluorescent in situ hybridization (FISH) test, which uses a special microscope to examine the number of copies of the gene.
Now labs have an alternative to FISH: The Spot-Light HER2 CISH test, approved this summer by the Food and Drug Administration. Unlike FISH, which must be used in a darkroom with ultraviolet light (a feature not all pathology labs have), CISH uses a stain that makes the HER2 genes distinctive enough to be measured using an ordinary microscope in natural light.
Studies show that CISH is as accurate as FISH in confirming whether a tumor is HER2-positive. However, until pathologists become more experienced at working with CISH, it’s probably best for labs to continue using FISH, says Elizabeth Hammond, MD, a professor of pathology at the University of Utah and a former member of the College of American Pathologists’ board of governors. She adds: “As with any medical procedure, you want that test done by someone who does it all the time.”
