AB 54. Lung infiltration from small cells TTF-1+, CD56+: is always small cell carcinoma?
Background: The presentation of two cases with similar morphological and immunohistochemical findings could be corresponded to small cell carcinoma of the lung, but ultimately they were considered as lymphoblastic lymphoma.
Patients and methods: Two patients, 33-year-old and 35-year-old men, respectively, of which the first was operated (VATS) for anterior mediastinal mass with pressure effects. A transbronchial biopsy was performed for the second patient who complained for dyspnea and hemoptysis. The specimens were evaluated in paraffin sections of hematoxylin-eosin and immunohistochemistry.
Results: It was observed in both cases diffuse infiltration of small cells with scant cytoplasm, nuclear molding and finely granular chromatin. There were areas with crash artifacts. Immunohistochemically in the first case was observed expression for TTF-1, ki67 (90%), CD3, TdT, CD10, and were negative for keratin AE1/AE3 and 8/18, CD56, CD20, CD30. In the second case was observed expression for CD56, ki67 (90%), CD3, TdT, while it was negative for TTF-1, CD10, keratin AE1/AE3 and 8/18, CD20, CD30. Finally the diagnosis in both cases was confirmed as T lymphoblastic lymphoma. In the second case, we were lately informed that, the patient was treated at the age of 9-yearold, in ermany, for T lymphoblastic lymphoma, with bone marrow transplantation.
Conclusions: The infiltration of the lung parenchyma by small cells with intense crush artifacts, do not always correspond to small cell lung carcinoma. Immunohistochemical stains have to perform for TTF-1, CD56, ki67, chromogranin, synaptophysin and keratin. The keratin was considered as primitive indicator for carcinoma, thus we don’t forget it from the immunohistochemical panel. The CD56, as is known, can be coexpressed in hematological diseases as indicator premature neoplastic cells, and also the TTF-1 expressed in carcinomas of the thyroid and occasionally in other carcinomas. The absence of expression of keratin AE1/AE3 or 8/18 in our cases, we removed from the initial estimate of small cell carcinoma, followed by additional immunohistochemistry were led to the correct diagnosis of lymphoblastic lymphoma.
