A 68-year-old woman presents with a lump in the soft tissue of her neck. Physical examination reveals a 0.5-cm subcutaneous tumor. Biopsy of the mass shows a benign neoplasm. The patient is told that she has the most common soft tissue tumor. What is the appropriate diagnosis?

Lipoma is composed of well-differentiated adipocytes and is the most common soft tissue mass. This benign, circumscribed tumor can originate at any site in the body that contains adipose tissue, but most appear in the subcutaneous tissues of the upper half of the body, especially on the trunk and neck. Lipomas are encountered mainly in adults. Histologically, a lipoma is often indistinguishable from normal adipose tissue. Fibroma (choice A) and leiomyoma (choice B) are benign neoplasms of fibroblasts and smooth muscle cells, respectively. Pleomorphic adenoma (choice D) is a mixed neoplasm of the salivary gland.Diagnosis: Lipoma