[CASE OF LOW-RISK PROSTATE CANCER WITH LYMPH NODE METASTASIS IN THE ANTERIOR PROSTATIC FAT TISSUE].

A 78-year-old man with a prostate-specific antigen level of 10 ng/mL was referred to our hospital. Magnetic resonance imaging revealed a Prostate Imaging-Reporting and Data System category of 5 in the apex transition zone. Transrectal and transperineal prostate needle biopsies were performed at a total of 20 sites. A well-differentiated adenocarcinoma with a Gleason score of 3+3 was detected on the right peripheral zone of the biopsied specimen. There were no apparent metastases, and robot-assisted radical prostatectomy was performed (Lesion 1: 30 mm lesion with a Gleason score of 4+5, EPE1, RM1, ly0, v0, pn1, sv0 in the bilateral transitional zones; Lesion 2: 4 mm lesion with a Gleason score of 3+3, EPE0, RM0, ly0, v0, pn0, sv0 in the left peripheral zone). Lymph node metastasis was found in the separately submitted anterior prostatic fat tissue. Removal of the anterior prostatic fat tissue is a simple procedure and is considered useful for evaluating the stump, and in this hospital, the tissue is routinely submitted for pathological diagnosis. It is extremely unlikely that lymph nodes will be found in the anterior prostatic fat tissue, and it is even less likely that any lymph node in the tissue will contain lymph node metastases. We therefore report a case of incidental discovery of lymph node metastasis in the anterior prostatic fat tissue at our hospital.