Chapter 129. Neoplasms of Subcutaneous Fat

Thomas Brenn

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Neoplasms of Subcutaneous Fat at a Glance

Adipocyte tumors are the most frequently encountered group of mesenchymal neoplasms. This is due to the high prevalence of lipoma and angiolipoma.
Tumors range from entirely benign neoplasms (e.g., lipomas) to those of intermediate malignant potential with risk for local recurrence (e.g., atypical lipomatous tumor) to high-grade pleomorphic sarcomas (e.g., pleomorphic liposarcoma).
Although liposarcoma is the single most frequently encountered sarcoma, the large majority of adipocyte tumors are benign.
The clinical presentation of adipocyte tumors is generally nonspecific.
Most adipocyte tumors show distinctive cytogenetic abnormalities that may be of diagnostic value.
Treatment is surgical excision. Adjuvant radiation therapy and/or chemotherapy may be of benefit for treatment of malignant tumors that are not amenable to complete excision or in cases of advanced disease.

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Lipoma at a Glance

Lipoma is the most common soft-tissue tumor.
It is benign and presents in adulthood as a small circumscribed mass. The anatomic distribution is wide with relative sparing of the head, hands, and feet.
Histologically, the tumors are circumscribed, encapsulated, and composed of mature white adipose tissue.

Epidemiology

Lipomas are the most common soft-tissue neoplasm. Although they affect individuals in a wide age range, they occur predominantly in adults between the ages of 40 and 60 years; presentation in childhood is rare. There is no gender predilection. Lipomas are multiple in approximately 5% of cases.1

Etiology and Pathogenesis

The majority of lipomas (approximately 75%) show karyotypic abnormalities. The cytogenetic findings are heterogeneous, but rearrangements of 12q13–15 are most common.2–4 Other affected loci are on chromosomes 6 and 13.2–4 Numerical abnormalities are scarce, and most tumors are diploid.

Clinical Findings

The most common presentation is as a painless, slowly enlarging mass involving the subcutaneous tissue of the trunk, neck, or proximal extremities. Involvement of the head, hands, and feet is uncommon. These superficial lipomas are typically small, measuring less than 5 cm.1 Lipomas may be multiple and familial and show a predilection for the arms and thighs in familial multiple lipomatosis (Fig. 129-1).5 The constellation of multiple lipomas, macrocephaly, lymphangiomas, and hemangiomas is known as Bannayan (Bannayan–Zonana) syndrome.6,7 This autosomal dominant disease shares features with other independently described entities and is currently also referred to as Bannayan–Riley–Ruvalcaba syndrome.8,9 Further clinical findings include intestinal polyposis, genital pigmented macules, and other hamartomas. The syndrome is caused by mutations in the PTEN gene and belongs to the larger family of PTEN hamartoma-tumor syndromes, including Cowden disease.10–15 Lipomas may also be seen as a manifestation of Gardner's syndrome. Gardner's syndrome is part of the spectrum of familial adenomatous polyposis and includes extracolonic manifestations such as desmoid fibromatosis, osteomas, cysts, and lipomas.