It is nonetheless the most common tumor derived from fibrous connective tissue that occurs primarily in infants and young children.
IMF tumors are benign in the sense that they do not metastasize to distant tissues although when occurring in the viscera, i.e. internal organs, carry guarded to poor prognoses and can be life-threatening, particularly in newborns and young infants.
[4][5] A minority of infantile myofibromatosis tumors present in individuals with a strong family history of the disease.
[8] They may be evident at birth in up to 60% of cases[4] but generally go undetected until they[9] are diagnosed in the first year of life,[8] uncommonly in older infants and young (<10 years/old) children,[4] or rarely in older children and adults (one individual was diagnosed with IMF at 85 years of age).
[1] At least 9 IMF cases described in the English literature were diagnosed in fetuses based on the findings of fetal spectrogram and/or magnetic resonance imaging.
[6] Subsequent studies have found that up to 70%[12] of individuals with IMF and no family history of the disease also carry mutations in one of their two PDGFRB genes in the cells of their tumor tissues.
[16] Further studies are needed to define NOTCH3 gene mutation's frequency of occurrence in, and contribution to the development of, IMF.
[7] This form of IMF, particularly in cases with tumors involving the gastrointestinal tract, heart, and/or lung,[6] has a far higher morbidity and mortality than the other forms[8] with death occurring in infants during the first weeks to 4 months of life[4] in 30–70% of cases[9] Death is typically due to a tumor's compression of vital organs or tissues (e.g. blood vessels).
Immunohistochemical analyses indicate that the spindle-shaped cells strongly express smooth muscle actin, calponin, and, less commonly, desmin proteins.
[9] When activated, the PDGFβ receptor's 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.
[22][23] Infantile digital fibromatosis, a tumor that develops primarily in the fingers and toes, had been regarded as a type of IMF.
Solitary IMF tumors typically grow slowly, produce few or no symptoms, and often regress spontaneously within 18 to 24 months of diagnosis.
Visceral solitary IMF tumors that cause significant tissue injury, are located in vital areas, and/or are life-threatening have been treated by surgical excision or, if surgery is deemed inappropriate, are treated with drugs and/or radiation therapy as indicated in the following section on multiple tumors (with visceral involvement).
[10] In rare cases, aggressive IMF tumors have recurred after regressing and required further observation and/or treatment.
[4] Multiple tumors (no viscera involvement) also may regress spontaneously and carry a good to excellent prognosis even when they invade local tissues.
These tumors typically respond to conventional systemic chemotherapy with reductions in their sizes; these responses are usually observed only after several weeks of therapy.
[9]); 2) imatinib should be the initial choice and dasatinib or ponatinib be used for cases failing to respond to imatinib in cases where the PDGFRB gene mutation has not been defined;[1] and 3) the inhibitors precise dosages for use in newborns and infants are not well-defined, have serious side-affects, and therefore should only be considered for refractory, life-threatening IMF tumors.