A single institutional experience treating adipocytic tumors: incidence, disease-related outcomes, and the clinical significance of MDM2 analysis

Adipocytic tumors exist either as a benign or malignant form. The benign variant, lipoma, is composed of normal fat tissue. Lipomas typically develop from superficial fat cells beneath the skin or mucous membranes. Liposarcoma, the malignant counterpart, often develops in deeper tissues and is the most commonly diagnosed Soft Tissue Sarcoma (STS), comprising at least 20% of adult STS. However, malignant tumors of fatty origin exist as a spectrum of diagnoses, each carrying a unique risk of recurrence, metastasis, and longterm survival. The World Health Organization classifies liposarcomas into five categories: i) Atypical Lipomatous Tumors/Well Differentiated (ALT/WD); Ii) Dedifferentiated (ALT/DD); Iii) Myxoid; Iv) Round cell; and v) Pleomorphic. Lipomatous tumors often exhibit different immunohistochemical patterns. Benign lipomas are distinguished by the absence of Murine Double-Minute 2 (MDM2) amplification. Similarly, ALT/WD, classically defined as a low-grade and locally aggressive tumor, demonstrates consistent patterns of MDM2 amplification. Some studies suggest 10% of ALT/WD progress to the highgrade DD form, with others report a dedifferentiation rate of as high as 20% for primary ALT/WD based on location. The ALT/DD subtype is aggressive and has a high capacity to metastasize. While the mechanism of pathogenesis of ALT/DD metastasis is unknown, previous studies suggest that increased MDM2 amplification may play a role. This study sought to evaluate a single institutional experience treating the entire spectrum of lipomatous tumors and describe utilization patterns of MDM2 testing. The group hypothesized: i) Atypical Lipomatous Tumors (ALT), which include ALT/DD and ALT/WD, would exhibit a higher rate of local recurrence than lipomas with no significantly increased incidence of metastases; and ii) at least 50% of our MDM2 testing of ALT would prove positive for the MDM2 overamplification. This study retrospectively reviewed 105 cases (66 lipomas, 27 ALTs, 12 liposarcomas) of patients who underwent lipomatous tumor excision at our institution from 2013 to 2017. Twenty-five tumors (6 lipomas, 18 ALT, 1 liposarcoma) were tested for MDM2 amplification. Three of the tested tumors recurred (2 ALT, 1 liposarcoma), and each exhibited MDM2 overamplification. Five tumors (5 liposarcoma) developed late metastases. These data suggest that although ALT is associated with a higher rate of local recurrence, metastases are quite rare. Additionally, the data demonstrate a high rate of positive MDM2 testing (76%) based on clinical and imaging characteristics of the tumors.