Cytologic Findings in Granular Cell Tumors, with Emphasis on the Diagnosis of Malignant Granular Cell Tumor by Fine-needle Aspiration Biopsy

Background: Granular cell tumors (GCTs) are uncommon tumors of putative schwannian derivation that are rarely malignant. Although recent studies have addressed a histologic correlation with malignant behavior, similar studies have not been done on cytologic material.

Methods: The authors evaluated 3 malignant GCTs and 17 benign GCTs (comprising 17 fine-needle aspiration biopsy samples and 3 samples from direct scrapes) for the following cytologic features: hyperchromasia; coarse chromatin; nuclear-to-cytoplasmic (N/C) ratio; nuclear pleomorphism; and vesicular nuclei with enlarged nucleoli, mitoses, necrosis, and spindle cell morphology.

Results: Hyperchromasia, coarse chromatin, increased N/C ratio, nuclear pleomorphism, and vesicular nuclei with enlarged nucleoli and spindle cell morphology were associated the most closely with malignancy when they were present throughout the cytologic sample. All were diffusely present in three of three malignant tumors, except vesicular nuclei and spindle cell morphology, which were present diffusely in two tumors and focally in one tumor. By contrast, although one to five of these features were present focally in 8 of 17 benign GCTs, none was present diffusely in any benign GCTs, with one exception, which had a combination of focal nuclear pleomorphism and hyperchromasia together with diffuse vesicular nuclei, large nucleoli, and coarse chromatin. The N/C ratio in this tumor was not increased, and there were no spindle cells or mitoses. Mitoses were present in 2 of 3 malignant GCTs and absent from all 17 benign GCTs. Necrosis was not seen in any tumors.

Conclusions: Malignant GCTs have characteristic cytologic features that differ from those of benign GCTs. However, morphologic heterogeneity precludes definitive classification of some tumors by cytologic features alone.