Introduction: Fibrous hamartoma of infancy (FHI) is a benign, soft tissue tumor that usually occurs in children and has a characteristic histological morphology. Objective: To describe a case of congenital FHI with atypical histological and clinical characteristics. Clinical case: Full-term male newborn, with no perinatal morbid history was referred to dermatology due to a congenital erythematous plaque in the umbilical region. The histological study showed a fusocelullar proliferation in dermis and hypodermis of biphasic distribution, with an infiltrative, swirling pattern and bundles of spindle fibroblast-like and myofibroblast-like cells, associated in depth with a mature adipose tissue component. The immunohistochemical study revealed diffuse positivity for CD34, and focal positivity for FXIIIa, without immunoreactivity for actin, desmin, MyoD1, S100, HMB45, Melan-A, or EMA. Fluorescent in situ hybridization (FISH) was negative for platelet-derived growth factor receptor beta (PDGFR-beta) and for ETV6 gene. PDGFR-beta and ETV6 gene are present in congenital dermatofibrosarcoma protuberans and infantile fibrosarcoma, respectively. This history, in addition to previous histological findings, supported the diagnosis of FHI. Surgical resection was performed, without signs of recurrence during clinical follow-up. Conclusion: It is important to consider the FHI within the differential diagnosis of subcutaneous tumors in children, especially in those under two years of age. Although its behavior is benign, it is similar to multiple benign and malignant lesions, which makes it imperative to perform a histological study in front of suspicious clinical lesions.

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