RB1 and neoplasm: First, we defined high-confidence RB1-defective (n = 19) and -proficient (n = 28) samples using both the protein abundance and phosphorylation status of Rb (pRb) in TCGA’s Clinical Proteomic Tumor Analysis Consortium (CPTAC) mass spectrometry proteomic dataset (Materials and Methods: Discovery of RBNSigs).