Immunohistochemical expression of PAX5 and TdT by Merkel cell carcinoma and pulmonary small cell carcinoma

A potential diagnostic pitfall but useful discriminatory marker

Ravindra Bharat Kolhe, Michelle D. Reid, Jeffrey R Lee, Cynthia Cohen, Preetha Ramalingam

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Background: Merkel cell carcinoma is a high-grade neuroendocrine carcinoma of skin that is characterized by immature cells which, because of its striking morphologic similarity, may be confused with other small round blue cell tumors such as pulmonary small cell carcinoma or lymphoblastic leukemia/lymphoma. Immunohistochemistry is therefore paramount to ensuring accurate diagnostic distinction between these tumors. The aim of our study was to evaluate and compare the expression of PAX5 and Terminal deoxynucleotidyl transferase (TdT), in Merkel cell carcinoma and pulmonary small cell carcinoma. Design: PAX5 and TdT immunohistochemical stains were performed on 27 Merkel cell carcinomas and 10 pulmonary small cell carcinomas. Results: PAX5 was expressed in 24/27 (89%) Merkel cell carcinomas and 0/10 (0%) pulmonary small cell carcinomas. TdT was expressed in 21/27 (78%) Merkel cell carcinomas and 9/10 (90%) pulmonary small cell carcinomas. Conclusions: Our study confirms that PAX5 and TdT expression can be expressed in a high percentage of Merkel cell carcinomas and so when positive are not diagnostic of lymphoblastic leukemia/lymphoma. When dealing with metastatic lesions, PAX5 negativity would favor a diagnosis of pulmonary small cell carcinoma over Merkel cell carcinoma. In addition, TTF-1 negative pulmonary small cell carcinoma is to be differentiated from Merkel cell carcinoma.

Original languageEnglish (US)
Pages (from-to)142-147
Number of pages6
JournalInternational Journal of Clinical and Experimental Pathology
Volume6
Issue number2
StatePublished - Aug 30 2013

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Merkel Cell Carcinoma
Small Cell Carcinoma
DNA Nucleotidylexotransferase
Lung
Precursor Cell Lymphoblastic Leukemia-Lymphoma
Neuroendocrine Carcinoma
Neoplasms
Coloring Agents
Immunohistochemistry
Skin

Keywords

  • Lung
  • Merkel cell carcinoma
  • PAX5
  • Small cell carcinoma
  • TdT

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Histology

Cite this

Immunohistochemical expression of PAX5 and TdT by Merkel cell carcinoma and pulmonary small cell carcinoma : A potential diagnostic pitfall but useful discriminatory marker. / Kolhe, Ravindra Bharat; Reid, Michelle D.; Lee, Jeffrey R; Cohen, Cynthia; Ramalingam, Preetha.

In: International Journal of Clinical and Experimental Pathology, Vol. 6, No. 2, 30.08.2013, p. 142-147.

Research output: Contribution to journalArticle

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abstract = "Background: Merkel cell carcinoma is a high-grade neuroendocrine carcinoma of skin that is characterized by immature cells which, because of its striking morphologic similarity, may be confused with other small round blue cell tumors such as pulmonary small cell carcinoma or lymphoblastic leukemia/lymphoma. Immunohistochemistry is therefore paramount to ensuring accurate diagnostic distinction between these tumors. The aim of our study was to evaluate and compare the expression of PAX5 and Terminal deoxynucleotidyl transferase (TdT), in Merkel cell carcinoma and pulmonary small cell carcinoma. Design: PAX5 and TdT immunohistochemical stains were performed on 27 Merkel cell carcinomas and 10 pulmonary small cell carcinomas. Results: PAX5 was expressed in 24/27 (89{\%}) Merkel cell carcinomas and 0/10 (0{\%}) pulmonary small cell carcinomas. TdT was expressed in 21/27 (78{\%}) Merkel cell carcinomas and 9/10 (90{\%}) pulmonary small cell carcinomas. Conclusions: Our study confirms that PAX5 and TdT expression can be expressed in a high percentage of Merkel cell carcinomas and so when positive are not diagnostic of lymphoblastic leukemia/lymphoma. When dealing with metastatic lesions, PAX5 negativity would favor a diagnosis of pulmonary small cell carcinoma over Merkel cell carcinoma. In addition, TTF-1 negative pulmonary small cell carcinoma is to be differentiated from Merkel cell carcinoma.",
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