Significance of the diagnostic categories "atypical" and "suspicious for malignancy" in the cytologic diagnosis of solid pancreatic masses

Endoscopic ultrasound guided (EUS) fine-needle aspiration (FNA) investigation of solid pancreatic lesions has been shown to have good sensitivity and specificity. Many lesions can be definitely classified as benign or malignant but some can only be cytologically classified as "atypical" or "suspicious for malignancy". Risk for malignancy in these indeterminate categories has not been well categorized. The cytology records of four University Medical centers were searched for all EUS guided FNAs of solid pancreatic lesions. All cases with a diagnosis of "atypical", or "suspicious for malignancy" were selected for analysis when histologic biopsy or over 18 months clinical follow-up was available. Two hundred and ninety-two cases with a diagnosis of "atypical" or "suspicious for malignancy" and adequate follow-up were obtained from the combined data of the four institutions. The percentage malignant for the categories "atypical" and "suspicious for malignancy" were 79.2 and 96.3%, respectively. If the category "atypical" was classified as benign and "suspicious for malignancy" was classified as malignant, the resulting positive predictive value was 96.3 (95% CI: 92.6-98.5) and the negative predictive value 20.8 (95% CI: 13.4-30.0). The categories of "atypical" and "suspicious for malignancy" stratify risk for malignancy in a fashion, which may aid in patient counseling and selection of follow-up protocols. Classification of "suspicious for malignancy" as malignant optimizes diagnostic sensitivity and specificity.