title: Expression of TdT in Merkel cell carcinoma and small cell lung carcinoma.
abstract: Merkel cell carcinoma (MCC) is an uncommon tumor with indistinct clinical features. The differential diagnosis includes small cell lung carcinoma (SCLC). We characterized the expression of terminal deoxynucleotidyl transferase (TdT) and a panel of immunohistochemical markers in 40 MCC, 30 SCLC, and 6 pulmonary carcinoid tumor (PCT) cases. We used antibodies against TdT, thyroid transcription factor (TTF)-1, cytokeratins (CKs) 7 and 20, chromogranin, and synaptophysin. Immunostaining was recorded semiquantitatively. Of 40 MCC cases, 28 (70%) were positive for TdT, showing, on average, more than 25% of tumor cells reactive with moderate nuclear staining intensity. TTF-1 (1 [3%]), CK7 (2 [5%]), CK20 (35 [88%]), chromogranin (29 [73%]), and synaptophysin (39 [98%]) were expressed in the MCCs. Of the 5 CK20- MCC cases, 4 were positive for TdT. SCLC showed expression of TTF-1 (23/30 [77%]), CK7 (22/30 [73%]), chromogranin (16/30 [53%]), and synaptophysin (22 [73%]) and no CK20 (0%) expression. Of 30 SCLC cases, 2 (7%) were positive for TdT. TdT may be beneficial in rare cases of CK20- MCC and may assist in distinguishing between MCC and SCLC. There is significant immunohistochemical variability and overlap between these 2 tumors.
authors.affiliation: Dept of Pathology, Sunnybrook Health Sciences Centre, University of Toronto, 2075 Bayview Ave, Toronto, Ontario, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Sidiropoulos
authors.forename: Wedad
authors.initials: W
authors.lastname: Hanna
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Raphael
authors.forename: Zeina
authors.initials: Z
authors.lastname: Ghorab
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002276:Carcinoid Tumor / Q000378:metabolism / Q000473:pathology; D015266:Carcinoma, Merkel Cell / Q000378:metabolism* / Q000473:pathology; D002864:Chromogranins / Q000378:metabolism; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D053554:Keratin-20 / Q000378:metabolism; D053552:Keratin-7 / Q000378:metabolism; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009687:Nuclear Proteins / Q000378:metabolism; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology; D055752:Small Cell Lung Carcinoma / Q000378:metabolism* / Q000473:pathology; D013194:Staining and Labeling; D016708:Synaptophysin / Q000378:metabolism; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D002864:Chromogranins; D053554:Keratin-20; D053552:Keratin-7; C000614412:NKX2-1 protein, human; D009687:Nuclear Proteins; D016708:Synaptophysin; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; D004253:DNA Nucleotidylexotransferase