Cutaneous Desmoplastic Leiomyosarcoma Development at Smallpox Vaccination Site

Area of Science:

• Dermatopathology
• Oncology
• Surgical Pathology

Background:

• Subcutaneous tumors require accurate diagnosis to differentiate benign from malignant conditions.
• Desmoplastic spindle cell lesions present a diagnostic challenge in surgical pathology.
• The differential diagnosis for firm subcutaneous tumors includes various mesenchymal and melanocytic neoplasms.

Observation:

• An 81-year-old male presented with a 4-year history of a slowly enlarging, firm, subcutaneous tumor on his left upper arm.
• The lesion's location at a prior smallpox vaccination site was noted.
• Histopathology revealed a desmoplastic spindle cell proliferation.

Findings:

• Immunohistochemical staining showed spindle cells positive for desmin and caldesmon, indicating smooth muscle differentiation.
• Strong and uniform p53 positivity was observed.
• Exclusion of symplastic leiomyoma, desmoplastic melanoma, and cutaneous spindle cell carcinoma was based on specific immunophenotypic and histopathologic features, leading to a final diagnosis of desmoplastic leiomyosarcoma.

Implications:

• Accurate clinicopathologic correlation and immunohistochemistry are crucial for diagnosing rare soft tissue tumors.
• Desmoplastic leiomyosarcoma, though rare, should be considered in the differential diagnosis of desmoplastic spindle cell lesions.
• Staged surgical excision is a necessary treatment modality for complete tumor eradication.