title: Primary Colon Adenosquamous Carcinoma in a Patient With Lynch Syndrome: A New Histologic Subtype Associated With Microsatellite Instability?
abstract: We report a case of a 53-year-old woman who presented with rectal bleeding and a 9.5 cm hemicircumferential ascending colon mass. Histology revealed adenosquamous carcinoma (ASC), a rare subtype comprised of malignant squamous and glandular elements. Immunohistochemistry revealed loss of MLH1/PMS2 expression and retained MSH2/MSH6 expression in squamous and glandular components, indicative of microsatellite instability (MSI). MSI is caused by loss-of-function defects in DNA mismatch repair genes, leading to increased susceptibility to a variety of neoplasms; the role of MSI in colorectal ASC is unknown. The tumor was negative for MLH1 gene promoter hypermethylation, the patient had a germline MLH1 mutation, and met criteria for Lynch syndrome. To our knowledge this is the first report of a MSI-high colorectal carcinoma (CRC) showing adenosquamous histology. Further evaluation of MSI status in colorectal ASC may be warranted as this may be another histologic type of CRC associated with MSI.
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, USA veduncan@uabmc.edu.
authors.forename: Virginia E
authors.initials: VE
authors.lastname: Duncan
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Shuko
authors.initials: S
authors.lastname: Harada
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Stevens
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis; D018196:Carcinoma, Adenosquamous / Q000175:diagnosis / Q000473:pathology*; D003110:Colonic Neoplasms / Q000175:diagnosis / Q000473:pathology*; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000175:diagnosis / Q000473:pathology*; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D000070957:MutL Protein Homolog 1 / Q000235:genetics; D016133:Polymerase Chain Reaction
chemical_list: D014408:Biomarkers, Tumor; C501486:MLH1 protein, human; D000070957:MutL Protein Homolog 1
keywords: Lynch syndrome; adenosquamous carcinoma; microsatellite instability