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Presented by Pedram Argani, M.D. and prepared by Bahram R. Oliai, M.D.
Case 3: 69-year old male with inguinal lymphadenopathy.
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1. Question
Week 52: Case 3
69-year old male with inguinal lymphadenopathy./images/2076a.jpg
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Answer: Merkel cell carcinoma involving lymph node
Histology: The lymph node is partially effaced by a uniform proliferation of primitive small round blue cells. These cells have fine delicate chromatin, and focally show nuclear molding. The mitotic rate is high. The cells have uniform round nuclear contours. These are the typical cytologic features of Merkel cell carcinoma. Tumor cells are immunoreactive for cytokeratin 20 but not for TTF-1, which identifies the tumor as Merkel cell carcinoma.
Discussion: Both lymphoblastic lymphoma and primitive granulocytic sarcomas could yield lymph node lesions composed of similar blastic-appearing cells. However, such lesions should be immunoreactive for leukocyte common antigen (CD45) and often CD43 but not for cytokeratin. Small cell carcinoma of the lung is typically immunoreactive for thyroid transcription factor (TTF-1) and not for cytokeratin 20.
The most likely scenario in this case is that the patient has a primary Merkel cell carcinoma of the skin, which may have regressed or had been excised but not reported to us. Rosai has postulated that Merkel cell carcinomas might rarely arise primarily in lymph nodes (AJSP 1992;16: 658-666).
Incorrect
Answer: Merkel cell carcinoma involving lymph node
Histology: The lymph node is partially effaced by a uniform proliferation of primitive small round blue cells. These cells have fine delicate chromatin, and focally show nuclear molding. The mitotic rate is high. The cells have uniform round nuclear contours. These are the typical cytologic features of Merkel cell carcinoma. Tumor cells are immunoreactive for cytokeratin 20 but not for TTF-1, which identifies the tumor as Merkel cell carcinoma.
Discussion: Both lymphoblastic lymphoma and primitive granulocytic sarcomas could yield lymph node lesions composed of similar blastic-appearing cells. However, such lesions should be immunoreactive for leukocyte common antigen (CD45) and often CD43 but not for cytokeratin. Small cell carcinoma of the lung is typically immunoreactive for thyroid transcription factor (TTF-1) and not for cytokeratin 20.
The most likely scenario in this case is that the patient has a primary Merkel cell carcinoma of the skin, which may have regressed or had been excised but not reported to us. Rosai has postulated that Merkel cell carcinomas might rarely arise primarily in lymph nodes (AJSP 1992;16: 658-666).
