Pulmonary Benign Metastasizing Leiomyoma: A Retrospective Analysis of Seven Cases Including a Rare Coexistence with In Situ Mucinous Adenocarcinoma.

Pulmonary benign metastasizing leiomyoma (PBML) is a rare condition characterized by histologically benign smooth muscle tumors occurring at extrauterine sites, often in women with a history of uterine leiomyoma. While PBML generally exhibits indolent behavior, its pathogenesis, management, and malignant potential remain unclear. This study retrospectively analyzes the clinical characteristics, imaging features, diagnostic approaches, pathological findings, treatment strategies, and outcomes of seven patients with PBML treated at our institution between January 2016 and May 2025. Seven patients were included, with a mean age at diagnosis of 48.9 ± 5.6 years. Two patients presented with respiratory symptoms. Imaging revealed multiple bilateral pulmonary nodules in four patients and solitary nodules in three. Six patients were diagnosed via video-assisted thoracoscopic surgery, and one through computed tomography-guided percutaneous biopsy. Immunohistochemistry revealed positivity for SMA and Desmin in all cases, ER in six, and PR in five, with the Ki-67 labeling index ≤3% in six patients. One patient had a coexisting in situ mucinous adenocarcinoma within the PBML lesion. All had a history of uterine leiomyoma. After diagnosis, one patient received hormonal therapy, and another underwent right adnexectomy. The remaining patients were managed with surveillance without additional treatment. During follow-up, one patient developed distant organ metastasis. PBML is a rare, typically indolent condition with potential for metastasis. Accurate diagnosis relies on imaging, histopathology, and immunohistochemistry. This study reports a unique case of PBML coexisting with intratumoral in situ mucinous adenocarcinoma, a previously unreported finding that may broaden the known histopathological spectrum.