Metastasizing leiomyoma is a rare condition characterized by the development of benign-appearing smooth muscle neoplasms at extrauterine sites in patients with a history of uterine leiomyoma. These lesions occur most commonly in the lung, with the abdominopelvic and mediastinal lymph nodes being other reported sites. Malignant transformation of metastasizing leiomyoma is extremely rare, with only a few cases described in the literature. We describe a case of metastasizing leiomyoma with malignant transformation in a middle-aged Asian lady, who developed pulmonary metastatic foci 12 years after surgical excision of the original uterine leiomyomata. Molecular analysis showed a common RAB2A-PLAG1 fusion gene and identical single nucleotide variants in both tumor foci, with significantly more pronounced segmental chromosomal copy number variations in one focus showing high-grade features. A comprehensive review of the literature lends support to the hypothesis that the original leiomyomata and the metastatic foci are clonally related, with high-grade features being associated with more complex genomic signatures.
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