Infantile Myofibromatosis

Infantile myofibromatosis (IMF) is a rare tumor found in 1 in 150,000 to 1 in 400,000 live births. 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.IMF tumors occur in three clinical patterns: 1) solitary IMF tumors (also called myofibromas) which often regress spontaneously and rarely cause serious issues; 2) multiple tumors (no viscera involvement) which consists of numerous (i.e. dozens to >100) IMF lesions most of which are located in the skin, subcutaneous tissues, and non-visceral but not visceral organs, may regress spontaneously, and rarely cause serious issues; and 3) multiple tumors (with viscera involvement) (also called generalized myofibromatosis) which rarely regress spontaneously and consist of numerous IMF lesions in non-visceral tissues plus one or more visceral tumors that may be life-threatening.A minority of infantile myofibromatosis tumors present in individuals with a strong family history of the disease. These familial cases are associated with mutations in either the PDGFRB or NOTCH3 gene. However, most IMF cases have no family history of the disease but nonetheless have PDGFRB gene mutations in their tumor cells; these mutations are similar to those occurring in the familial PDGFRB gene mutations. Regardless of these genetic variations, all IMF tumors consist of bland-appearing, benign (i.e. non-malignant) myofibroblasts, i.e. 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 gene’s protein product.