Rare Cutaneous Metastasis of Low-Grade Retroperitoneal Leiomyosarcoma

Retroperitoneal leiomyosarcoma (RPL) is a rare smooth muscle malignancy that often presents silently and is typically diagnosed at an advanced stage. Cutaneous metastases from RPL are uncommon and usually indicate high-grade disease with a poor prognosis. To date, there are no published reports of low-grade RPL metastasizing to the skin. We report the case of a 55-year-old female who initially presented with intermittent abdominal pain and was diagnosed with a 5.1 x 3.1 cm retroperitoneal mass. Following surgical resection, histopathologic examination confirmed low-grade leiomyosarcoma based on spindle cell morphology and low mitotic activity. The patient recovered well postoperatively, but 18 months later, she presented to dermatology with a firm, dusky, subcutaneous nodule on her right temporal hairline. A punch biopsy confirmed cutaneous metastasis of leiomyosarcoma. A subsequent lesion in the right antecubital fossa was also biopsied, showing identical histological features. Both lesions were excised. A follow-up PET scan showed no evidence of systemic metastasis. A third nodule later developed on the right cheek, prompting oncology follow-up due to concern for deep structural involvement. This is the first reported case of a histologically low-grade RPL metastasizing to the skin. While low-grade RPLs are considered less aggressive, this case highlights their potential for metastasis. Clinicians should maintain a high index of suspicion for cutaneous metastasis in patients with RPL who develop new skin lesions, even in cases with low histologic grade.