Sclerosing Atypical Lipomatous Tumor with Myxomatous Features Presenting in the Plantar Heel: A Case Report.

INTRODUCTION: Atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) is the most common liposarcoma subtype, but foot and ankle involvement is exceptionally rare, and plantar heel presentation is particularly uncommon. Such lesions may mimic benign soft-tissue masses, raising the risk of delayed diagnosis or unplanned excision and poorer oncologic outcomes. This case reports a rare sclerosing ALT with prominent myxomatous features arising in the plantar heel, confirmed by diffuse MDM2 immunohistochemical positivity; reports of this specific presentation are extremely limited in the literature. The case underscores the need for a broad differential in persistent or enlarging plantar masses, diagnostic use of magnetic resonance imaging (MRI) and histopathology, and planned excision with negative margins followed by long-term surveillance. CASE REPORT: A 61-year-old male presented with a slowly enlarging, mildly tender mass on the plantar right heel, measuring approximately 2.7 × 3.4 cm on exam as a firm, non-mobile subcutaneous mass. MRI showed a well-circumscribed, T1-hypointense/T2-hyperintense lesion with inhomogeneous enhancement. Marginal excision confirmed sclerosing ALT with myxomatous features, diffuse nuclear MDM2 IHC positivity, and negative margins. No recurrence was identified at 1-year follow-up. CONCLUSION: ALT should be considered in the differential for persistent or progressive plantar soft-tissue masses in middle-aged to older adults. Unplanned excision of foot sarcomas carries significant risk, including recurrence and dedifferentiation. This report is relevant to podiatric surgeons, orthopedic oncologists, and pathologists, and more broadly to surgical oncology, reinforcing MDM2 IHC, negative-margin excision, and long-term MRI surveillance as essential to management of ALT in rare anatomic sites.