ABSTRACT
Background
Fibrous hamartoma of infancy (FHI) is a rare soft tissue lesion arising as a subcutaneous mass involving the axilla, trunk, and upper arm in infants and children <2yrs. Sarcomatous transformation in FHI is described in anecdotal cases in the literature.
Case Report
We describe one such example arising as a mass in the lower back in a 3-month-old infant. On histology, the tumor contained classic triphasic morphology; however, brisk mitotic activity noted at multiple foci was diagnostically challenging to categorize. The tumor was evaluated for ETV6-NTRK3 fusion to exclude other common differentials.
Conclusion
While FHI may be frequently encountered in infants, rare sarcomatous transformation are known to occur and merits special attention as it can be misdiagnosed. Also, a close follow-up is warranted as the lesion is known to recur locally.
Keywords
Hamartoma; Neoplasms, Fibrous Tissue; Neoplasms, Connective Tissue; Neoplasms, Connective and Soft Tissue
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