Unilateral breast mass in an infant: a rare presentation of spontaneously regressing myofibromatosis

Breast tumors are very rare in infants. We describe a 4-month-old female infant who presented with a firm and painless right breast mass. It was first noticed at the age of 1 month and then gradually increased in size. Further physical examination and imaging studies revealed other subcutaneous masses and lytic bone lesions. True-cut biopsy from the breast lesion was consistent with infantile myofibromatosis. Infantile myofibromatosis is a group of uncommon mesenchymal tumors that tend to occur in infancy and regress spontaneously, as demonstrated in our case. Surgical excision of such lesion might have led to permanent loss of breast tissue. The report discusses the clinical, radiological, and pathologic features, in addition to the previously described treatment options for this condition.