Two smalls in one: Coincident small cell carcinoma and small lymphocytic lymphoma in a lymph node diagnosed by fine-needle aspiration biopsy

Background: B-cell chronic lymphocytic leukemia / small lymphocytic lymphoma (CLL / SLL) is one of the most common lymphoproliferative disorders in western countries. Patients with SLL / CLL are at increased risk of site-specific secondary cancers. We present a unique case of a 71-year-old male, with a history of SLL / CLL, who presented with pulmonary symptoms and a mediastinal mass. Fine needle aspiration (FNA) of the mediastinal lymph node revealed synchronous SLL / CLL and small cell carcinoma (SCC). Materials and Methods: The patient underwent a computed tomography (CT) scan of the chest and endobronchial ultrasound-guided transbronchial fine needle aspiration of the mediastinal lymph node (4R). The sample was submitted for cytopathology, immunohistochemical stains, and flow cytometry evaluation. Results: Fine needle aspiration of the mediastinal lymph node revealed neoplastic cells, in clusters and singly, with cytological features suggestive of small cell carcinoma. The immunohistochemistry results confirmed this diagnosis. Small-to-medium, mature-appearing lymphocytes were also present in the background. Flow cytometry analysis revealed that these lymphocytes possessed an immunophenotype consistent with CLL / SLL. Conclusions: This case illustrates the importance of a pathologist's awareness of the possibility of concurrent lymphoma and metastatic carcinoma in a lymph node. When evaluating lymph nodes, pathologists must strive to identify both foreign cells and subtle lymphoid changes. As demonstrated by our case, ancillary techniques (such as immunohistochemistry and flow cytometry) can be critical to making a complete and accurate diagnosis. The diagnosis of small cell carcinoma in the enlarged lymph node, primarily harboring CLL / SLL, is of critical importance for decision-making and treatment purposes, in addition to having a significant adverse impact on the overall survival.