Malignant granular cell tumor: a look into the diagnostic criteria

Fanburg-Smith et al. classified granular cell tumors (GCTs) using six criteria with high Ki-67 and p53 in malignant cases. We aim to refine their classification and reproduce their immunohistochemical findings. We, first, classified our 48 cases according to Fanburg-Smith criteria (37 benign, seven atypical, and four malignant), and performed Ki-67 and p53 on a sample of tumors. Then, we reclassified them into 44 benign and four with uncertain malignant potential (GCT-UMP) using only necrosis and/or mitoses. (1) According to Fanburg-Smith criteria: Malignant cases were significantly younger than benign and atypical ones; occurred predominantly in males; were significantly larger in size; and showed a higher Ki-67 expression but an insignificant difference in p53 staining. (2) Comparative findings: The four malignant cases according to Fanburg-Smith corresponded to our four cases with UMP. The seven atypical cases and our benign group shared similar means, except for age. None of these atypical cases recurred or metastasized. Despite its small number, our preliminary study showed similar selectivity of two more reproducible criteria (vs six) in the classification of cases of GCT with potential aggressive behavior, preserving a role for Ki-67 in difficult cases. However, metastases remain the sole definite criterion for malignancy.