Mast Cell Sarcoma in an Infant

Mast cell diseases comprise a spectrum of disorders including cutaneous mastocytosis, indolent or aggressive systemic variants including leukemia, and unifocal tumor formations such as benign extracutaneous mastocytoma or aggressive mast cell sarcoma (MCS). Many mast cell diseases are associated with aberrancy of c-KIT proto-oncogene resulting in tyrosine kinase activity, typically exhibiting point mutation in codon 816. MCS is an exceedingly rare clinicopathologic entity characterized by a unifocal accumulation of neoplastic mast cells that grow in a locally destructive manner. We report a case in a 2-year-old boy who was initially diagnosed at 8 months of age with atypical cutaneous mastocytoma of the right ear with subsequent aggressive, destructive growth pattern; features that were most consistent with MCS. So far, MCS has been documented in the literature in at least 6 human cases. To the best of our knowledge, our case represents the first MCS in an infant. Thorough multimodal approach with strict follow-up is relevant in appropriately diagnosing this rare entity, particularly in differentiating this lesion from other neoplasms that are more likely to occur in infancy.