title: Cancerous 'floater': a lesson learned about tissue identity testing, endometrial cancer and microsatellite instability.
abstract: A 46-year-old woman presented with endometrial cells on a pap smear and underwent endometrial curettage. The specimen revealed secretory endometrium and a possible endometrial polyp. In addition, a single 4 mm fragment of well-differentiated adenocarcinoma was found. Tissue identity DNA genotyping was performed and the adenocarcinoma tissue fragment showed a drastically different allelic pattern from that of the background endometrium. To confirm tissue contamination, genotyping of three other tumor specimens-probable sources for a contaminant-was performed but failed to identify a match. Without confirmation of contamination, a second endometrial curettage was obtained from the patient, in which similar adenocarcinoma tissue was once again found. Further workup demonstrated that the patient had a microsatellite unstable (MSI) endometrial adenocarcinoma by immunohistochemistry and molecular testing. The patient subsequently underwent staging surgery, which revealed an early-stage, well-differentiated endometrioid adenocarcinoma. This case study illustrates an uncommon, yet important caveat of tissue identity testing by DNA genotyping, where MSI instability can significantly alter the allelic pattern of DNA polymorphisms in the tumor genome, leading to erroneous conclusion regarding the tissue identity. Awareness of this phenomenon is crucial for a molecular pathologist to avoid interpretation errors of tissue identity testing in a cancer diagnostic workup.
authors.affiliation: Department of Pathology, Yale University School of Medicine, New Haven, CT06520-8023 , USA.
authors.forename: Veerle
authors.initials: V
authors.lastname: Bossuyt
authors.forename: Natalia
authors.initials: N
authors.lastname: Buza
authors.forename: Nhu T
authors.initials: NT
authors.lastname: Ngo
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Much
authors.forename: Maria C
authors.initials: MC
authors.lastname: Asis
authors.forename: Peter E
authors.initials: PE
authors.lastname: Schwartz
authors.forename: Pei
authors.initials: P
authors.lastname: Hui
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics*; D018269:Carcinoma, Endometrioid / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology / Q000601:surgery; D002454:Cell Differentiation; D003475:Curettage; D003951:Diagnostic Errors / Q000517:prevention & control; D016889:Endometrial Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology / Q000601:surgery; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007150:Immunohistochemistry; D053842:Microsatellite Instability; D008875:Middle Aged; D009367:Neoplasm Staging; D010641:Phenotype; D011237:Predictive Value of Tests; D014626:Vaginal Smears
chemical_list: D014408:Biomarkers, Tumor