The presence of cancer cells in tumor-adjacent healthy lung tissues was considered unlikely based on histopathology, the lack of expression of EGFR and ERBB2, expressed in respectively 73 and 69 percent of canine primary lung cancers (38), the lack of expression of proliferation markers used to identify replicating cells, and the analysis of differentially expressed genes and of biological process enrichments. Here, ERBB2 is linked to cancer.