For further molecular and cellular characterization of the desmoplastic reactions present in HapT1 tumors, this study examined the expression of two major extracellular matrix proteins (i.e., collagen and fibronectin) and two important cell types known to promote PC-associated fibrosis (i.e., myofibroblast-like and mast cells). The gene discussed is LYPLA1; the disease is pachyonychia congenita.