A clinical study showed that when breast cancer HER2 expression was measured using the HERmark assay, breast cancer patients with advanced disease whose tumors were HER2 positive by fluorescence in situ hybridization (FISH) but H2T low by HERmark had similar outcomes (as measured by time to progression, following treatment with trastuzumab) as those patients whose cancers were FISH negative and H2T low, thus identifying HER2 FISH-positive tumors with a poorer response to trastuzumab, relative to those tumors which were both HER2 positive by FISH and H2T high by HERmark [16]. This evidence concerns the gene ERBB2 and breast cancer.