Table 1:

Key histopathologic features of common differentials of GCGs

	GCG	GCT	ABC	Brown Tumor
Epithelioid stroma	Spindled stroma, oval-to-elongated nuclei	Plump epithelioid with oval nuclei	Spindled stroma, oval-to-elongated nuclei	Spindled stroma, oval-to-elongated nuclei with fibrous stroma dividing it into lobules
Giant cells	12 Nuclei in clusters around hemorrhagic foci	>12 Uniformly distributed nuclei	Smaller giant cells, in clusters, woven bone present, less hemorrhage	Few giant cells
Immunohistochemistry (p63 positivity)	Yes	Yes	No	No
Gene mutation
H3f3a mutation	No	Yes	No	No
USP6 rearrangement	No	No	Yes	No