A rare condition in which one or more fibrous (connective tissue) tumors form in the skin, muscle, or bone. Sometimes, they also form in internal organs. The tumors are usually benign (not cancer) and do not spread to other parts of the body, but they can grow large and damage nearby organs. They may go away without treatment. Infantile myofibromatosis occurs most often in the first 2 years of life, or it may be present at birth. It is a type of soft tissue tumor.