Unraveling cancer lineage drivers in squamous cell carcinomas.

Cancer hijacks embryonic development and adult wound repair mechanisms to fuel malignancy. Cancer frequently originates from de-regulated adult stem cells or progenitors, which are otherwise essential units for postnatal tissue remodeling and repair. Cancer genomics studies have revealed convergence of multiple cancers across organ sites, including squamous cell carcinomas (SCCs), a common group of cancers arising from the head and neck, esophagus, lung, cervix and skin. In this review, we summarize our current knowledge on the molecular drivers of SCCs, including these five major organ sites. We especially focus our discussion on lineage dependent driver genes and pathways, in the context of squamous development and stratification. We then use skin as a model to discuss the notion of field cancerization during SCC carcinogenesis, and cancer as a wound that never heals. Finally, we turn to the idea of context dependency widely observed in cancer driver genes, and outline literature support and possible explanations for their lineage specific functions. Through these discussions, we aim to provide an up-to-date summary of molecular mechanisms driving tumor plasticity in squamous cancers. Such basic knowledge will be helpful to inform the clinics for better stratifying cancer patients, revealing novel drug targets and providing effective treatment options.