MMP9 and hepatocellular carcinoma: Lu et al. generated a molecular atlas of the multicellular ecosystem of primary and metastatic HCC using single RNA sequencing that revealed seven TME subtypes of HCC, with the macrophage-dominated and lymphocyte-depleted microenvironments conferring the worst prognosis; these environments have a large population of MMP9+ TAMs, with PPARγ driving their terminal differentiation and thus HCC progression [25].