four instead of the normal two chromosomes for some but not all chromosomes), single chromosome gains for several chromosomes, and loss of heterozygosity in the p arms of chromosomes 1 and 11 in the first case and in the second case a loss of the p arm in chromosome 10, lose of chromosome 14, and lose of a portion of the q arm of chromosome 22q. These two cases along with recurrent EGFR gene abnormalities strongly support the notation that FHI is as neoplastic tumor. Diagnosis
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. The combination of these factors clearly distinguishes FHI from three recently defined tumors (i.e. fibroblastic connective tissue nevus, medallion-like dermal dendrocyte hamartoma, and plaque-like CD34-positive dermal fibroma) as well as various pediatric spindle-shaped cell neoplasms. Tumor imaging methods such as magnetic resonance imaging may also be helpful in suggesting that a tumor is an FHI. Treatment and prognosis
FHI tumors, if left untreated, have been documented to grow for as long as ~5 years following their diagnosis. The treatment of choice for these tumors is complete surgical excision with clear margins (i.e. with removal of all tumor tissue).
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. Sixty-eight percent of these cases were diagnosed in the first year of life, 23% were diagnoses at birth, and 9% were diagnosed in children 2–5 years old. The male-to female ratio was 2.4. The tumors were most common in the axilla (23% of cases), upper arm (12.5%), lower arm (10.5%), external genitalia area (9.5%),  and inguinal region (7.5%); less common or rare sites for these tumors were the buttocks, back of the head, back of the neck, back of the torso, lower arm, leg, foot, chest, and anal area. Most cases presented as solitary masses but 3 cases presenting with 2 tumors and 1 case presenting with 5 tumors. Overall, the size of these tumors varied between 0.5 and 4.0 cm but in rare cases were as large as 20 cm. Two subsequent studies of 145 and 60 individuals agreed with all of these results but also did diagnose  FHI in individuals as old as 8 and 14 years, respectively. Pathology
On gross pathological examination, FHI tumors are soft, poorly demarcated, fibro-fatty masses located in subcutaneous tissues. These tumor masses tend to blend with the surrounding fat tissues, may be lobulated, and in rare cases, especially when large, extend into nearby muscles, nerves, and/or fibrous/connective tissue structures.