Primitive non-neural granular cell tumor: Literature review

Primitive non-neural granular cell tumor (PNNGCT) is a rare mesenchymal neoplasm of unknown lineage with prominent cytoplasmic granularity. By reviewing the relevant literature reported over the past 30 years, we detail the clinicopathological features of these tumors and describe their immunostaining profile and differential diagnoses. These tumors are more common in children and young adults, and often involve the back and extremities. A panel of immunostains is important to rule out other differential diagnoses. For example, S-100 protein is the best differentiating marker to distinguish the more common “traditional” granular cell tumor from PNNGCT, and NKI-C3 and anaplastic lymphoma kinase (ALK) stains can be particularly helpful in confirming the diagnosis. In addition, an underlying ALK gene rearrangement has been reported in a small subset of cases. In general, the majority of these tumors appear to behave in a benign fashion, and conservative management is recommended.