AFST tumors commonly present as slowly growing, painless, deep-seated lumps in individuals aged 6 to 86 years old (median age 47-50 years in different studies). The tumors are most common in the lower extremities but uncommonly occur in the back, chest wall, iliac crest, groin and nearby lower lateral abdominal region, abdominal cavity, pelvic cavity, breast, cheek, temporal region of the head and, in a report on 24 AFST cases done in Shanghai, the upper limb in 3 cases and, in 1 case each, the retroperitoneum and liver. The tumors' longest diameters have ranged from 1.2 to 10 cm (mean: 5.1 cm) and 0.8 to 14 cm (mean: 4.6 cm) in two different studies. Pathology== Grossly, AFST tumors, when visible on skin, are located in the skin's subcutaneous<unk>  or the fascia layer below the subcutaneous<unk> . They may be infiltrating deeper into these<unk> s and/or into nearby large joints. Regardless of location, however, most of these tumors are well-circumscribed. Histopathological microscopic analyses of hematoxylin and eosin-stained AFST<unk> s generally reveal bland appearing spindle-shaped cells and a prominent small, thin-walled blood vessels network in a background of alternating myxoid connective<unk>  areas and more highly cellular collagen fiber-rich connective<unk>  areas. (Myxoid indicates areas that appear more blue or purple than normal due to their high uptake of the hematoxylin stain.) Typically, these tumors appear well-circumscribed but some cases show them infiltrating into adjacent normal adipose<unk> s, connective<unk> s, skeletal muscles, and/or joints. Immunohistochemistry analyses (i.e. identifying specific proteins in cells using antibodies that bind to these proteins) of AFST<unk> s detect cells bearing estrogen receptor, CD163 and NCOA2 proteins in 100% of cases; MUC1 (also termed EMA) protein in 46% of cases; desmin protein in 22% of cases; ACTA2 (also termed α-SMA), CD34, and STAT6 proteins in 10% or fewer cases, and S100 and cytokeratin proteins in no cases. Chromosome and gene abnormalities== In 60-80% of cases, the cells in AFST tumors express the AHRR-NCOA2 fusion gene. A fusion gene is a hybrid gene formed from two previously independent genes as a result of a translocation, interstitial deletion, or chromosomal inversion. The AHRR gene (i.e. gene for the aryl hydrocarbon receptor repressor protein) is located at band 15.33 on the short (or "p") arm of chromosome 5 (cite designation: 5p15.33); The NCOA2 gene (i.e. gene for the nuclear receptor coactivator 2 protein) is located at band 13.3 on the long (or "q") arm of chromosome 8 (cite designation: 8q13.3). A translocation between these two chromosomes creates the AHRR-NCOA2 fusion gene (fusion gene designation: t(5;8)(q15;q13)). AHRR is a tumor suppressor gene that when fused to other genes is found in the cells of , and thought to promote, various leukemias and neoplasms. It is thought to similarly promote the development and/or progression of AFST tumors. While most commonly associated with the AHRR-NCOA2 fusion gene, rare AFST tumor cases have also been shown to be associated with GAB1-ABL1, GTF2I-NCOA2, NCOA2-ETV4, ETV4-AHRR, and NAB2-STAT6 fusion genes.
Angiofibroma of soft tissue
Cellular angiofibroma
Juvenile hyaline fibromatosis
Lymphangioma
Lymphohemangioma
Peripheral ossifying fibroma
Cavernous hemangioma
Aponeurotic fibroma