Natural History and Malignant Risk Factors of Solid Pseudopapillary Tumors of the Pancreas

Background and Aim: Solid pseudopapillary tumors (SPTs) of the pancreas are unusual neoplasms of uncertain prognosis. Most patients with SPTs have a good prognosis after undergoing surgical resection, but there are rare cases in which a locally infiltrative growth pattern and metastatic variety are exhibited, or recurrence of the disease after surgery occurs; these cases have been reported with very poor clinical outcomes. Our study investigated the natural history of SPTs and delineated the clinicopathologic features that may predict the malignancy potential of the disease. Methods: A total of 100 patients with suspected SPTs were enrolled in our study and 77 patients underwent surgical resection. A resulting 60 tumors were pathologically proven to be SPTs and the affected patients were followed-up regularly after surgery. Clinical and pathologic data for all 100 patients were analyzed. Results: Of the 60 total patients with histologically positive SPTs, 55 (92%) were women and 5 (8%) were men. The median patient age was 34 years (range, 13-77 years). Among the 60 patients, 9 had malignant SPTs and 51 had benign SPTs. Deep parenchymal invasion into the surrounding tissue was the most frequent pathologic feature suggesting malignancy (75%) among the 60 patients who underwent surgical resection. Patient clinicopathologic characteristics and demographic factors were compared between those who had benign SPTs and those who had malignant SPTs. There were no significant differences in the various patient features between the 2 groups, including age, sex, symptoms, tumor size, tumor location, internal tumor composition, pattern of tumor calcification, tumor necrosis, hemorrhage, and immunohistochemical tumor tissue patterns. There were 2 patients who had distant metastasis; 1 presented with distal metastasis in the liver and the other patient had recurrence of cancer with a peritoneal mass after surgery. Metastasectomy was performed on the 2 patients and there was no mortality or disease progression during the follow-up period (median, 143 months; range, 53-319 months). Conclusion: Solid pseudopapillary tumors are low-grade tumors that have a generally good prognosis. However, the clinical development and malignancy potential of SPTs are neither fully understood nor predictable, even with histologically benign tumors. Further investigations in tumor biology, along with long-term patient follow-up, may provide insight into the disease process and clinical development of SPTs.