Solid Pseudopapillary Neoplasms of the Pancreas: Clinicopathologic Analysis and a Predictive Model.

Solid pseudopapillary neoplasms (SPNs) of the pancreas are rare. They are considered low-grade malignancies, and a small percentage of patients experience recurrence or metastasis. It is critical to investigate associated biological behavior and identify patients at a risk of relapse. This was a retrospective study of 486 patients with SPNs who were diagnosed between 2000 and 2021. Their clinicopathologic features, including 23 parameters and prognoses were analyzed. Six patients (1.2%) presented with synchronous liver metastasis. A total of 21 patients experienced recurrence or metastasis postoperatively. The overall and disease-specific survival rates were 99.8% and 100%, respectively. The 5- and 10-year relapse-free survival (RFS) rates were 97.4% and 90.2%, respectively. Tumor size, lymphovascular invasion, and the Ki-67 index were independent predictors of relapse. Furthermore, a Peking Union Medical College Hospital-SPN risk model was built to evaluate the risk of relapse and compared it with the American Joint Committee on Cancer tumor staging system (eighth edition, 2017). Risk factors included 3 parameters: tumor size (>9 cm), lymphovascular invasion status (presence), and Ki-67 index (>1%). Risk grades were available for 345 patients, who were divided into 2 groups: (1) low risk (n = 124) and (2) high risk (n = 221). The group with no risk factors was designated as low risk and had a 10-year RFS of 100%. The group associated with 1 to 3 factors was designated as high risk, with a 10-year RFS of 75.3%. Receiver operating characteristic curves were generated, and the area under the curve was 0.791 for our model and 0.630 for the American Joint Committee on Cancer with respect to the cancer staging system. We validated our model in independent cohorts and demonstrated a sensitivity of 98.3%. In conclusion, SPNs are low-grade malignant neoplasms that rarely metastasize, and the 3 selected pathologic parameters can be used to predict their behavior. A novel Peking Union Medical College Hospital-SPN risk model was proposed for routine application to guide the patient counseling in clinical practice.