In about 50% of these cases, these somatic mutations were the same as those found in familial IMF with the remaining cases having mutations in other sites of the gene. These other somatic mutation sites included 2 cases of p.Asp850Val (Asp=aspartate, Val=valine), 2 case of p.Asn666Lys (Asn=asparagine, Lys=lysine), and concurrent double mutations p.Arg561Cyt plus Asp666Lys in one case and p.Trp566Arg (Trp=tryptophan) plus AspN666Lys in another case. Three cases had more complex mutations involving multiple gene sites with two of them having the p.Asn666Lys mutation gene in combination with other mutations. PDGFRB gene
The PDGFRB gene product, the PDGFβ receptor, is normally highly expressed in fibroblasts and other cells of mesenchymal origin including vascular smooth muscle cells. When activated, the PDGFβ receptors tyrosine kinase stimulates cell signaling proteins such as phosphatidylinositol-3 kinase, STAT proteins, phospholipase Cγ, and GRB2 which in turn promote their parent cells to grow, proliferate, and survive for abnormally prolonged times. The PDGFβ receptor gene is a proto-oncogene, i.e. a normal gene that when mutated could form a cancer-causing oncoprotein. Studies show that the PDGFRB mutant proteins in IMF are constitutively overactive and that the tyrosine kinase inhibitor imatinib blocks the activity of the p.Arg561Cys and p.Asn666Lys mutants as well as the p.Arg561Cyt plus Asp666Lys and p.Trp566Arg plus AspN666Lys double mutants but not the p.Asp850Val mutant. Two other tyrosine kinase inhibitors, dasatinib and ponatinib, do inhibit the p.Asp850Val mutants tyrosine kinase activity. Limited initial studies suggest that these inhibitors are useful in treating severe cases of IMF.
cells that blend a variable set of features seen in fibroblasts, the most common cell type in connective tissue, with a variable set of features seen in smooth muscle cells.Treatment of IMF tumors depends upon the tumor numbers, locations, and genetic abnormalities found in each individual and often include more than one therapeutic regimen. Individuals with solitary tumors are usually treated by observation with the expectation that many of these tumors will regress spontaneiously. Single tumors located in vital areas (e.g. intracranial tumors) and tumors that do not regress over suitable observation periods are often treated by surgical removal. Multiple tumors (with viscera involvement) and surgically inaccessible life-threatening IMF tumors have been treated with one or a combination of chemotherapy drugs, radiation therapy or, in tumors with certain PDGFRB gene mutations, drugs directed specifically against this mutated genes protein product. Presentation
IMF tumors are usually painless, well-encapsulated, rubbery to hard, and freely movable-to-fixed masses. They may be evident at birth in up to 60% of cases but generally go undetected until they are diagnosed in the first year of life, uncommonly in older infants and young (<10 years/old) children, or rarely in older children and adults (one individual was diagnosed with IMF at 85 years of age). The tumors may be flesh-colored papules or nodules; plaques (i.e. flat-topped papules that are equal to or greater than 10 mm in largest diameter); pedunculated, calcified masses; or ulcerated, necrotic masses. Most of these tumors are <1 cm in diameter but can be much larger, e.g. 5.2 cm in diameter.