An ultrasound image of the right axilla showed a nondiagnostic solid mass measuring 2.3 × 1.3 × 5.7 cm. Hematoxylin-eosin–stained sections revealed different-sized lobules in the mid and lower dermis and subcutaneous tissue surrounded by moderately cellular connective tissue. The smallest lobule was a terminal duct lobular unit. The wall of the lobular unit and duct consisted of 1 layer of columnar cells. There also were terminal ducts merging with somewhat larger ducts. Some of these larger ducts had myoepithelial cells at the periphery of the columnar cells. In addition, hair follicles and apocrine and eccrine glands were present.
Axillary Mass in a 20-Year-Old Woman. Arch Dermatol. 2001;137(10):1367-1372. doi: