Folliculosebaceous Poromas With PAK2 and PAK3 Rearrangements: A Report of Two Cases and Review of the Literature.

We report two cases of folliculosebaceous poroma (holocrine poroma) harboring gene rearrangements involving members of the p21-activated kinase (PAK) family. Both tumors were composed of small poroid cells with ductal and sebaceous differentiation and demonstrated strong nuclear GATA3 expression on immunostaining. In one case, fluorescence in situ hybridization (FISH) demonstrated a PAK2 rearrangement; in the other, a PAK3 rearrangement was identified. Although GATA3 has been proposed as a useful marker to distinguish clonal seborrheic keratosis from hidroacanthoma simplex, its strong expression in PAK2/PAK3-rearranged folliculosebaceous poromas suggests limited specificity in this differential context. Notably, to our knowledge, this represents the first reported case of a benign poroma harboring a PAK3 rearrangement. These findings support a role for PAK gene fusions that may contribute to sebaceous differentiation in folliculosebaceous poroma and underscore the molecular heterogeneity of poromas.