[Tumor infiltrates suspicious of carcinoma in mediastinal lymph nodes].

Myelosarcomas are, due to their rarity, a difficult differential diagnosis. Not infrequently, extensive immunohistochemical staining for characterization of the tumor is performed, if one does not directly think of myelosarcoma. In the present case, there was a positivity of the myeloid blasts for cytokeratin. This may complicate the discrimination of myelosarcoma from carcinoma, in particular small cell carcinoma, not only in the mediastinum, but also in the skin, e.g., Merkel cell carcinoma.