Pulmonary Metastases of a Uterine Smooth Muscle Tumour with Undefined Malignancy Potential.

Smooth muscle neoplasms with atypical proliferative behaviour, but without clear histopathological malignancy represent a diagnostic and therapeutic challenge, as distinction from a sarcoma can be difficult and no guaranteed treatment recommendations are available due to the rarity of these changes. In the event of uncertain primary histology, even metastases cannot be assessed as malignancy criteria, but may contribute to the clarification of the histology. Similarities with other smooth muscle proliferations, such as lymphangioleiomyomatosis, are striking. The diagnostic difficulties and treatment options are explained based on the example of a 59-year-old patient, in whom a retroperitoneal mass and pulmonary lesion of such a tumour occurred 4 years after a hysterectomy. Even though the genesis and histological diagnostics have not been conclusively clarified, slow growth and a low recurrence rate for post-menopausal patients allow for a wait-and-see approach, whereby the option for anti-hormonal treatment exists in the event of positive evidence of hormone receptors.