Histopathological, Immunohistochemical and Clinical Features of Granular Cell Tumors: Re-Evaluation of Malignancy Criteria in a Series of 54 Tumors

<i>Aim.</i> Granular cell tumors (GCTs) are mostly benign. Malignant GCTs are extremely rare. Although the criteria proposed by Fanburg-Smith et al are widely used, some authors do not find them especially useful. We aimed to present our GCT case series consisting of 54 patients from 2 institutions during a 22-year period and evaluate these tumors according to these criteria of malignancy. <i>Materials and Methods</i>. Fifty-four patients with GCT diagnosed between 2000 and 2024 were retrospectively reviewed. All hematoxylin/eosin-stained slides were evaluated for spindling pattern, nucleolar prominence, pleomorphism, geographical necrosis, increase in nuclear/cytoplasmic ratio, and mitotic index. <i>Results</i>. Overall, 7 tumors were classified as "Malignant GCT." Histopathologically all malignant tumors showed nucleolar prominence and pleomorphism. Ki-67 proliferation index was 3% or higher in 6 tumors. In 4 of the malignant GCTs, lymph node metastasis was present at the time of diagnosis. In 2 of these patients, lung metastasis and in 1 patient liver metastasis were also found. Another malignant tumor showed bone invasion. In one of the malignant tumors, local recurrence, lymph node metastasis, and lung metastasis occurred 1 year after excision. <i>Conclusions</i>. Malignant GCTs had behaved as frequently metastasizing high-grade sarcomas.