PSMD4 and cancer: In general, cancer was shown to co-express (strong positive correlation) at least five PSM gene clusters (1) PSMD1, PSMD11-12, PSME3-4, 2) PSMA3-4, PSMA6, PSMC6, 3) PSMA2, PSMA5, PSMA7, PSMB2, 4) PSMB1, PSMB3-7, PSMC1, PSMC3, PSMC5, PSMD4, PSMD9, PSMD13, PSMG3, and 5) PSMB8-10, PSME1-2.