Lipomas growing in internal organs can be more dangerous; for example, lipomas in the gastrointestinal tract can cause bleeding, ulceration, and painful obstructions (so-called "malignant by location", despite being a benign growth histologically). Malignant transformation of lipomas into liposarcomas is very rare, and most liposarcomas are not produced from pre-existing benign lesions. A few cases of malignant transformation have been described for bone and kidney lipomas, but it is possible that these few reported cases were well-differentiated liposarcomas in which the subtle malignant characteristics were missed when the tumor was first examined. Deep lipomas have a greater tendency to recur than superficial lipomas because complete surgical removal of deep lipomas is not always possible.The presence of multiple lipomas, lipomatosis, is more commonly encountered in men. Some superficial lipomas can extend into deep fascia and may complicate excision. Liposarcoma is found in 1% of lipomas and is more likely to occur in lesions of the lower extremities, shoulders, and retroperitoneal areas. Other risk factors for liposarcoma include large size (>5 cm), associated with  calcification, rapid growth, and/or invasion into nearby structures or through fascia into muscle tissue. Epidemiology
Around 2% of the general population has a lipoma. These tumors can occur at any age, but are most common in middle age, often appearing in people from 40 to 60 years old.
Genetic studies in mice have shown a correlation between the HMG I-C gene (previously identified as a gene related to obesity) and lipoma development. These studies support prior epidemiologic data in humans showing a correlation between HMG I-C and mesenchymal tumors.Cases have been reported where minor injuries are alleged to have triggered the growth of a lipoma, called a "post-traumatic lipoma". However, the link between trauma and the development of lipomas is controversial. Other conditions
Lipomatosis is believed to be a hereditary condition in which multiple lipomas are present on the body.Adiposis dolorosa (Dercum disease) is a rare condition involving multiple painful lipomas, swelling, and fatigue. Early studies mentioned prevalence in obese postmenopausal women. However, current literature demonstrates that Dercum disease is present in more women than men of all body types; the average age for diagnosis is 35 years.Benign symmetric lipomatosis (Madelung disease) is another condition involving lipomatosis. It nearly always appears in middle-aged males after many years of alcoholism, but nonalcoholic males and females can also be affected. Diagnosis
A physical exam is typically the easiest way to diagnose it. Rarely, a tissue biopsy or imaging may be required. The imaging modality of choice is magnetic resonance imaging (MRI) because it has superior sensitivity of distinguishing it from liposarcoma as well as mapping the surrounding anatomy. Treatment
Usually, treatment of lipomas is not necessary, unless they become painful or restrict movement.