Granular cell tumors can occur at many sites. Most are benign but some can behave in a malignant fashion. A number of criteria can help to identify a malignant granular cell tumor.
Malignant granular cell tumor have:
(1) metastasis (with exclusion of multifocal tumors)
(2) definite vascular invasion
Pathologic findings that may indicate malignant behavior:
(1) size (> 5 cm)
(2) tumor necrosis
(3) mitotic activity (> 2 mitoses per 10 high power fields at 200x)
(4) spindle cells
(5) high Ki-67 index (>= 10%)
(6) nuclear pleomorphism and hyperchromasia
(7) vesicular nuclei with large nucleoli
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