Solid-pseudopapillary tumor of the pancreas showing a remarkable reduction in size over the 10-year follow-up period

An 18-year-old healthy woman was admitted to our department for further evaluation of a pancreatic mass (45 mm in diameter) by transabdominal ultrasound at a general health check. Solid-pseudopapillary tumor (SPT) was suspected from the findings of diagnostic images. Therefore, surgery was recommended. The patient and her family, however, refused surgery. Ultrasound-guided transcutaneous biopsy revealed proliferation of tumor cells with small nuclei showing a pseudopapillary arrangement. PAS positive granules and alpha-1-antitrypsin positive cells were proven, which led to the diagnosis of SPT. As the grade of atypism of the tumor cells was low, the patient underwent follow-up examination once a year at our outpatient department thereafter. The tumor gradually decreased its maximum diameter in 10 years from 45 mm to 15 mm. Thus far, there have been very few reports on the natural course of SPT, and this is the first report describing marked spontaneous shrinkage of a tumor in a long follow-up period.