ERBB2 and breast carcinoma: However, if the patient has HER2 positive breast cancer, the utilization of ERBB targeted therapy may offer therapeutic benefit for both cancers.59 This study was conducted prior to the approval of tucatinib for mCRC and therefore was not used for patients in this study.60 The optimal choice of HER2 targeted therapy with a dual diagnosis of breast and CRC has not yet been determined.