A case of recurrence of a solid pseudopapillary neoplasm of the pancreas effectively treated with proton beam radiotherapy.

We report a case of a male in his 50 s who underwent pancreaticoduodenectomy for solid pseudopapillary neoplasm (SPN) of the pancreas at 30 years. He developed a liver abscess 15 years after the surgery, and CT scan revealed a swollen retroperitoneum lymph node and a tumor in the liver. Symptoms, including abdominal distension, appetite loss, and epigastric pain, appeared due to lymph node metastasis. Endoscopic ultrasonography-guided fine-needle aspiration against the lymph node revealed SPN recurrence. The tumor had invaded the common hepatic artery, and surgery was not indicated. Chemotherapy of Gemcitabine/nab-Paclitaxel biweekly was performed 8 times; however, no reduction in tumor size was observed, and the patient's symptoms worsened. Proton beam therapy (67.5 GyE in 25 fractions) was subsequently performed for lymph node metastasis, and led to a gradual reduction in lymph node metastasis, and an improvement in symptoms. No re-expansion of lymph node metastasis has been observed 3 years after proton beam therapy. Since SPN is low malignancy and most cases can be expected to be cured by surgery, there is currently no standard treatment of unresectable SPN. This case is the first report of proton beam therapy for SPN, and was considered to be effective.