[A case of metastatic renal cell carcinoma associated with Birt-Hogg-Dubé syndrome treated with molecular-targeting agents].

A 56-year-old man was referred to our clinic because of left lumbar pain and a left solitary renal tumor (9. 8 cm in diameter) and bilateral pulmonary metastases detected by computed tomographic scan. Pathologic diagnosis following open radical nephrectomy was papillary renal cell carcinoma, G2, pT2aN0M1. Subsequently, the patient was sequentially treated with interleukin-2 (3 months (mo), progressive disease (PD)), interferon-alpha (3 mo, PD), and oral S-1 as a clinical trial (28 mo, PD). Because of skin fibrofolliculomas, pulmonary cysts, and spontaneous pneumothorax history, Birt-Hogg-Dubé (BHD) syndrome was suspected during the treatment course, despite his having no family history of the disease. Subsequent genetic testing revealed a FLCN germline mutation (c. 1285dupC). He was started on molecular-targeting therapies sequentially, i.e., sorafenib (1 mo, PD), sunitinib (4 mo, PD), and everolimus (7 mo, PD). The patient died of progressive disease at 78 mo from the initial nephrectomy and 30 mo from the start of targeted agents. Loss of FLCN function has been shown to result in the upregulation of the PI3K/mTORC1 pathway in both in vitro experiments and in vivo FLCN knockout mice models. Despite its use as the sixth-line systematic treatment, the mTOR inhibitor everolimus exhibited a relatively long-term effect as compared with the previously used tyrosine kinase inhibitors and in contrast to the results in the RECORD-1 clinical trial. This finding may provide insight into the molecular mechanism of BHDassociated renal tumors.