The American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) changed the guidelines that determine which breast cancers are considered HER2-positive in 2013. According to a recent study from the Mayo Clinic, those changes have doubled the number of patients being diagnosed with HER-2 positive breast cancer. The study, "Change in Pattern of HER2 Fluorescent in Situ Hybridization (FISH) Results in Breast Cancers Submitted for FISH Testing: Experience of a Reference Laboratory Using US Food and Drug Administration Criteria and American Society of Clinical Oncology and College of American Pathologists Guidelines," was published in the Journal of Clinical Oncology. "The new guidelines were established to reduce the number of equivocal cases, where HER2 status is uncertain, but we found that they did just the opposite," Robert Jenkins, MD, PhD, the Ting Tsung and Wei Fong Chao professor of individualized medicine research and professor of laboratory medicine and pathology at Mayo Clinic, and the study's senior author, said in a press release. "The number of equivocal cases went up, resulting in additional testing and a much larger number of women with cancers ultimately labeled as HER2-positive." HER2-positive breast cancers, characterized by high levels of the HER2 protein or by the presence of extra copies of the HER2 gene, tend to be more aggressive and to spread at a faster pace than other breast cancers.