The most common benign neoplasm of the breast is fibroadenoma, which typically occurs in the upper outer quadrant of the breast in women between the ages of 20 and 35. These lesions originate from the terminal duct lobular unit and histologically reveal a mixture of fibrous connective tissue and ducts. Clinically, fibroadenomas are rubbery, freely movable, oval nodules that usually measure 2 to 4 cm in diameter. Numerous neutrophils are seen in acute bacterial infection of the breast (acute mastitis), which is usually seen in the postpaum lactating or involuting breast. Dilation of the breast ducts (ectasia) with inspissation of breast secretions is characteristic of mammary duct ectasia, which is common in elderly women. If large numbers of plasma cells are also present, the lesion is called plasma cell mastitis. Fat necrosis of the breast, associated with traumatic injury, is characterized by necrotic fat surrounded by lipid-laden macrophages and a neutrophilic infiltration. Fibroadenoma Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition