Fibrous hamartoma of infancy (FHI) is a rare, typically painless, benign tumor that develops in the subcutaneous tissues of the axilla (i.e. armpit), arms, external genitalia, or, less commonly, various other areas.
[5] In 2020, the World Health Organization classified FHI in the category of benign fibroblastic and myofibroblastic tumors.
In this study, most individuals presented with a slowly growing, symptomless, subcutaneous mass although rarely these masses were rapidly growing, and/or were tender, painful, warm, and/or were accompanied by skin changes, pigmentation, sweat gland enlargement, and/or increased hair overlaying the tumor.
On gross pathological examination, FHI tumors are soft, poorly demarcated, fibro-fatty masses located in subcutaneous tissues.
[2] Earlier Immunohistochemical analyses of FHI tumor tissues in a small number of cases have given varying results.
[11] The EGFR gene which codes for the production of the epidermal growth factor receptor protein is located at band 11.2 on the short (or "p") arm of chromosome 7.
These two cases along with recurrent EGFR gene abnormalities strongly support the notation that FHI is as neoplastic tumor.
[5] The diagnosis of FHI is dependent on its presentation as a subcutaneous tumor that often occurs in individuals at birth or ages <1–2 years old; its highly characteristic histopathology consisting of fibroblast/myofibroblast, adipose tissue, and myxoid zones; and its content of tumor cells which have one of the EGFR gene mutations described in the previous section.