ERBB2 and neoplasm: Furthermore, conversion from HER2 positive primary tumor to HER2 negative metastases, and vice versa was determined, as well as conversion from HER2 negative tumor to heterogeneous HER2 expression levels in different metastases in the same patient.27, 28 In 3 of 16 patients, treatment was changed as a direct consequence of the new knowledge of the HER2-status.