A 19-year-old female presents to your office complaining of an enlarging mass over her right anterolateral deltoid. On examination, she has a visible soft-tissue lump over the anterolateral aspect of her shoulder. It is relatively nontender to palpation and has some mobility with relation to the underlying muscle. There is no overlying skin problem. She denies numbness, tingling, or weakness distally. She has no complaints other than the mass is visible and would like it removed. MRI is shown in Figure 8–27.

Figure 8–27

Based on the MRI result, which of the following is true?

1. She should have it removed, with histology and genetic testing of the specimen

2. Due to high recurrence rate, it should not be removed

3. She should get preoperative radiation followed by wide resection

4. Over time the lesion will regress on its own, and it should be treated with conservative symptomatic treatment

Discussion

The correct answer is (A). The MRI demonstrates a lipoma, which is a benign tumor of fat. In this case, the tumor is located in the deltoid musculature. There are fibrous septae and blood vessels within the lesion that could indicate an atypical lipomatous tumor (ALT). If any atypia is seen on histology, MDM-2 FISH testing should be performed, which is positive in ALTs. Since this is a large deep lesion, it should be removed and tested. Atypical lipomatous tumors do not metastasize but can recur. In a small percentage of cases, these tumors can dedifferentiate into a malignant tumor.

She proceeds with surgery, and the lesion is found on final pathology report to be MDM2-positive. What should you tell her at her follow-up visit?

1. She will need to return to the operating room for repeat wide resection

2. This is an atypical lipomatous tumor that has a higher recurrence rate than a typical lipoma, therefore should be watched with surveillance imaging more frequently and for longer duration than a typical lipoma

3. She will be referred to a medical oncologist to discuss this positive test

4. She should get radiation to the area since this test was positive

Discussion

The correct answer is (B). MDM2 is a marker that can be tested for by fluorescence in situ hybridization (FISH), which differentiates atypical lipomatous tumor from a plain lipoma. Atypical lipomas have a higher local recurrence rate, up to 50% at 10 years but do not metastasize. These tumors can be removed with marginal excision, however, patients should be followed more closely and for longer duration than lipoma patients due to the higher recurrence rate. These tumors do not require wide resection, chemotherapy, or radiation.

Objectives: Did you learn...?

Clinical and imaging features of lipoma?

To differentiate between lipoma and atypical lipomatous tumor, both clinically and genetically?