Adenosquamous gallbladder carcinoma: Multigene hotspot mutational profiling reveals a monoclonal origin of the two components.

Adenosquamous carcinoma (ASC) of the gallbladder is a rare malignant tumor that is characterized by a coexisting of glandular and squamous components. In a case of ASC, we performed hotspot multigene mutational profiling of 164 hotspot regions of eleven cancer-associated genes (AKT1, APC, BRAF, CTNNB1, KIT, KRAS, NRAS, PDGFRA, PIK3CA, PTEN and TP53) in the two microdissected components. Both tumor phenotypes resulted characterized by a p.E542K point mutation in the PIK3CA gene, whereas adenocarcinoma component revealed also a TP53 Q331* homozygous stop mutation. Of note, coexisting high-grade dysplastic epithelium was characterized by a mixed cell population, with an upper part featuring a glandular differentiation and a basal layer of p63 positive (squamous committed) cells. Overall these data provide evidence of an early squamous differentiation of the lesion with a common genetic landscape of the two components.