Background : Solid pseudo-papillary neoplasm(SPN) is mostly defined as benign looking behavior. However, it may have an aggressive clinical course in some cases. Several studies to find clinical predictor for aggressive pattern have done. Among these, we planned to find clinical correlation between SPN’s biologic behavior and pre-operative PET/CT classification.

Methods : A total of 84 patients diagnosed with SPNs were analyzed retrospectively from October 2000 to November 2020 and additional Ki-67 staining were done. Survival outcomes were analyzed depending on PET/CT classification and Ki-67 expression patterns.

Results : Patients in pre op PET/CT class III showed the highest mean Ki -67 index value (11.27  2.17) than other group after analyzing resected specimen pathologically. Even though, overall survival and disease free survival showed no difference depending on pre op PET/CT classification, more than half of recurred patients (57.14%, 4 of 7) were categorized as pre op PET/CT class III.

Conclusions : Patients with pre op PET class III showed relatively high Ki-67 index levels and high correlation with the possibility of recurrence. These high proliferative pathologic features may lead poor outcome in case of SPN. Thus, we should not overlook SPN PET class III as it will be always benign, but we expect that it will be helpful in predicting the prognosis of the patients and determining the follow up period in advance.