men (10:1 male-to-female ratio) aged 45–70 years (mean age 54 years) with a predilection for arising in the shoulder, posterior neck, and upper back. However, a recent retrospective review of 27 patients with this disease found that it occurred mostly in men (2:1 male-to-female ratio), 18 to 80 years old (average age 56.5 years), ranged from 2 to 10 cm in size, and was located most commonly either in the flank/paraspinal (24% of cases), neck (20%), shoulder (16%), foot/ankle (12%), or other (28%) areas. The tentatively classified cellular angiofibroma variant of MFB typically occurs in adults (women 40–50 years old, men 60–70 years old with rare cases in children), is usually a small tumor but can be as large as 25 cm, and frequently develops in the groin-scrotum or vulva-vaginal regions. Diagnosis Medical imaging may suggest but cannot prove that a tumor is MFB. Mammography, computed tomography scans, and magnetic resonance imaging of mammary and extramammary MFB typically show well-defined and well-circumscribed tumors which in almost all cases have no calcifications; these results suggest that the tumor is not malignant but do not indicate which type it might be. The diagnosis of MFB depends on the microscopic histopathology (i.e. appearances after proper tissue preparation and staining) of its pre-surgery biopsied issues. As shown in the upper image and the two images in the Additional images section seen below, both mammary and extramammary MFB tissues contain spindle cells, variable numbers of adipocytes (i.e. fat cells) and broad sheets or, less often, thick bundles of collagen fibers. About 4% of cases have an epithelial tumor cell-like morphology, i.e. the tissues are composed predominantly of epithelioid cells variably mixed with a minority (10% to 40%) of round, polygonal, and spindle-shaped cells. Unlike malignant tumors, MFB tumors do not have: a) atypical cells except in the rare cases which contain small clumps of multinucleated cells; b) rapidly proliferating cells as defined by measuring the proliferative index (i.e. fraction of cells undergoing mitosis); or c) areas of necrosis (i.e. areas of dead or dying cells). Microscopy of tumors in the spindle cell lipoma tentative variant of MFB show a mixture of mature fat cells, ropey collagen, and spindle cells in a myxoid (i.e. background connective tissue that stains blue or purple rather than the red of normal connective tissue) matrix. The blood vessels in these tumors often appear hyalinized. Tumor tissues in the tentative cellular