Birt-Hogg-Dubé Syndrome with Renal Cancer Treated as Multiple Metastases of Cancer of Unknown Primary.

A 60-year-old woman presented with multiple lung and bone metastases with unknown primary cancer. Chest CT images showed multiple pulmonary cysts, predominantly of the middle and lower lobes. She also had a history of pneumothorax. Four years after chemotherapy and radiation therapy, multiple hypervascular tumors eventually developed in the bilateral kidneys, suggesting the possibility of Birt-Hogg-Dubé (BHD) syndrome. Genetic testing revealed a folliculin mutation, which confirmed the diagnosis of BHD syndrome. When we encounter cancer of unknown primary with multiple pulmonary cysts in a patient with a history of pneumothorax, thorough imaging of the kidneys and genetic testing for BHD syndrome is necessary.