ERBB2 and metastatic neoplasm: We defined the onset of primary or secondary distant metastatic disease as discovering at least one of the following criteria: (i) undergoing chemotherapy for a minimum of five calendar quarters, (ii) undergoing HER2-targeted antibody therapy for a minimum of seven calendar quarters, (iii) taking medications that define distant metastatic disease for a minimum of two quarters, or (iv) histologic examination of putative malignant lesions (e.g., biopsies, paracentesis).