ERBB2 and breast carcinoma: For patients with metastatic HER2-positive breast cancer (23% of breast cancers in Mexico), the cost per patient of treatment with trastuzumab, pertuzumab, and chemotherapy doubles the cost for the treatment of patients with disease in earlier stages (38,796 v 21,000 USD) and is 154 times higher than the cost for patients with carcinoma in situ (stage 0), whose average is 251.45 USD.