MDK and skin squamous cell carcinoma: In primary cSCC, iCAFs and IL7R+ CAFs produced high levels of MDK to mediate their intercellular communications, while in recurrent cSCC, TSKs secreted high levels of MDK, whose receptors were expressed on TSKs and other cells, thus regulating the strong cell-cell interactions within TSKs (Figure 6B, Figure S9C, Figure S10).