Collision Tumor of Metastatic Lung Adenocarcinoma to Lower Limb Leiomyosarcoma: Case Report and Literature Review.
Mark Strong, Nicholas Frazzette, Fang Zhou et al.
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Case in brief
A 90-year-old man presented with a rapidly enlarging soft-tissue mass over the anterolateral right knee. Biopsy showed high-grade leiomyosarcoma, and imaging also identified a dominant pulmonary nodule. Resection of the knee mass revealed a separate glandular component alongside the sarcoma. Lung biopsy confirmed adenocarcinoma, and immunohistochemistry showed that the glandular cells in the knee lesion matched the lung tumor, supporting metastatic lung adenocarcinoma within the primary leiomyosarcoma.
What made this case unusual
The case represents tumor-to-tumor metastasis from lung adenocarcinoma into a malignant soft-tissue sarcoma, producing a carcinoma-sarcoma collision tumor.
Diagnostic / clinical pearl
When a soft-tissue sarcoma contains a distinct glandular component, histology and immunophenotyping can help distinguish metastatic carcinoma within the sarcoma from carcinosarcoma.
Why it matters
Correct classification of a biphasic soft-tissue lesion may inform oncologic planning for both tumor types.