This case illustrates a very rare clinical scenario of large cell transformation of mycosis fungoides (LCT-MF) with pulmonary involvement and granulomatous inflammation. Mycosis fungoides (MF) is a common type of cutaneous T-cell lymphoma, which often presents in the sixth decade with red, scaly skin patches and plagues predominantly on the lower trunk and sun-protected areas (1). The skin lesions are composed of abnormal cleaved small T-cell lymphocytes showing dermal and intra-epidermal infiltration. LCT-MF typically occurs in advanced MF cases, affecting approximately 20-50% of these patients (2). LCT-MF requires greater than 25% large atypical lymphoid cells, which are greater than 4 times the size of a small lymphocyte (1). The diagnosis of LCT-MF is typically made on a skin biopsy after a well-established diagnosis of MF has been made. Extracutaneous involvement, such as lymph node, bone marrow or lung involvement, may be seen in either patients with MF or those who have already demonstrated transformation in the skin. The cytomorphology of MF and LCT-MF has been well described in patients with extracutaneous involvement. Fine needle aspiration (FNA) of enlarged lymph nodes in patients with MF can show either a predominance of small lymphoid cells with significant nuclear irregularities or a mixed population of cells with a significant large cell population in the setting of LCT-MF (3). A diagnostic flow cytometric pattern is necessary to support the extracutaneous involvement by this cutaneous T-cell lymphoma characterized by a dominant CD4+ population of T-cells with loss of T-cell antigens typically associated with mature T-cells (1, 3, 4). Further molecular analysis, including analysis for clonal T-cell receptor gene rearrangements, may be necessary in some patients if flow cytometry is not diagnostic (3). Immunohistochemical staining including CD30 staining can be helpful; however only about 50% of cases of LCT-MF will show CD30 positive large cells and CD30 positivity is not specific for this lymphoma (5).

Granulomatous inflammation has been well described in association with lymphoid malignancies. Up to 2% of patients with cutaneous lymphomas can showed a marked granulomatous reaction, with the majority being seen in association with MF (6). However, granulomas can be seen even more frequently in Hodgkin lymphoma (9-13%), as well as with other T-cell lymphomas (6, 7). It is important to pay close attention to the cytologic characteristics of the cells in the background when encountering granulomatous inflammation on FNA as there may be atypical or malignant cells in the background (7). Tissue biopsy may be necessary to help definitively diagnose malignancy if there is an exuberant obscuring granulomatous reaction (7). During rapid on-site evaluation, keeping a broad differential can assist in assuring appropriate triage of the FNA samples. Furthermore, the importance of having the correct clinical history cannot be overemphasized as seen in this case. The clinical history of MF was provided; however, the on-site team was not aware of the known large cell transformation of MF in this patient. The presence of the large, atypical cells in the background of granulomas was therefore perplexing, although appropriate triage was performed.