ERBB2 and neoplasm: Furthermore, several additional prognostic factors have been suggested: Nulliparity, high tumor cell proliferation (KI-67), high tumor vessel density (angiogenesis), oncogene amplification or overexpression (HER2/neu, K-ras) and alterations of tumor suppressor genes (PTEN, p53, p21, p16) are believed to be associated with adverse prognoses.