PTCSC may pre-operatively be identified by detecting its characteristic cytological features in FNA smears, regardless of the proportion of SC within the tumor. Because clinical outcomes of PTCSC remain undetermined, it is imperative to postulate PTCSC as a differential diagnosis, even when classical nuclear features of PTC are present. Diagn. Cytopathol. 2017;45:391-398. © 2017 Wiley Periodicals, Inc.

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Malignant granular cell tumors (GCTs) account for less than 2% of all GCTs and mainly occur in the deep soft tissue of the thigh or trunk. Malignant GCTs are highly aggressive tumors with high rates of recurrence and metastasis. In this brief report, we describe a rare case of malignant GCT in a 64‐year‐old Japanese man who presented with a 14 × 20 cm mass in the left inguinal region. The cytologic findings of fine‐needle aspiration (FNA) revealed atypical epithelial‐like granular cells with granular substance in the background, which was difficult to differentiate from apocrine carcinoma or melanoma. The immunohistochemistry (IHC) findings of the needle biopsy revealed that the tumor cells were positive for S‐100 and lysosomal marker CD68 which was suggestive of a GCT. However, the presence of crush artifacts made it challenging to identify cellular atypia, which is a characteristic of malignant tumor. Taken together, the FNA and needle biopsy results were suggestive of malignant GCT. The importance of preoperative diagnosis of malignant GCT is well known, but few reports have described its cytological findings. In our brief report, we show that combining cytological FNA and biopsy findings with IHC findings achieves an accurate diagnosis of malignant GCT.

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