Molecular pathways involved in hair follicle tumor formation: all about mammalian target of rapamycin?

Hair follicle tumors show a broad range of phenotypic variability and diverse histopathological characteristics. To date, different genes and signalling cascades have been implicated in the development and growth of these tumors including the sonic hedgehog, nuclear factor kappa-B and wingless pathway. While the former three have received ample attention, little is known about the possible role of mammalian target of rapamycin (mTOR) in trichofollicular tumorigenesis. Here, we delineate how mTOR can link the various signalling pathways, thereby proposing a unifying model for hair follicle tumor formation.