Prior studies of metastatic breast cancer (some of which included all types of metastatic breast cancer and not just HER2-positive cancers, as well as both de novo and recurrent metastatic cancer) have shown that median OS declines with increasing age at diagnosis, with one study indicating that for each additional year of age at diagnosis, the hazard of death increases by 3% [14,15,16]. Here, ERBB2 is linked to metastatic malignant neoplasm.