Squamous Cell Carcinoma of Lung Metastatic to a Mediastinal Lymph Node Involved by Chronic Lymphocytic Leukaemia /Small Lymphocytic Lymphoma, A Case Report with Review of Literature

Abstract

Metastasis of a cancer to another coexisting tumor is a very rare event. When this occurs, it confers a diagnostic dilemma.  So far, only very few cases have been reported regarding primary squamous cell carcinoma metastatic to lymph nodes replaced by chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL), most of which were metastasis from primary skin cancers.  Here we present a rare case of squamous cell carcinoma of lung metastatic to CLL/SLL-involved mediastinal lymph node.  The patient was an 82-year-old male who had a history of CLL/SLL and recurrent stroke. His disease has been stable with a white cell count maintained around 60,000 for the previous 3 years without medication.  He presented with left-sided facial droop, confusion and slurred speech with a white cell count of 110,000.  CT Scan performed recently showed a 2.6 cm right lung mass with enlarged bilateral hilar and mediastinal lymph nodes.  Mediastinal lymph node biopsy was performed and sent for frozen section.  Frozen section was misinterpreted as “negative” due to diagnostic difficulty. On permanent sections, aggregates of cohesive epithelioid cells (Figure 1) were found in a background of homogenous population of small lymphocytes. The normal architecture of lymph node was effaced (Figure 5). The epithelioid cells showed increased nuclear/cytoplasm ratio, clumpy chromatin, and were positive for CK5/6 (Figure 2) and negative for BerEp4, Mucicarmine (Figure 2) and TTF-1 (Figure 1). The small lymphocytes in the background were positive for CD5, CD20 and CD23 (Figure 6-8), and negative for CD3.  These morphological and immunohistochemical features are diagnostic for poorly differentiated squamous cell carcinoma metastatic to a lymph node involved by CLL/SLL. We compared this case with other similar cases available in the literature and discussed diagnostic pitfalls in such situation.