Improving diagnostic yield of pancreatic serous cystadenoma with cyst fluid ancillary testing, adjunct immunohistochemistry, and additional fine-needle biopsy sampling.

Background: Fine-needle aspiration (FNA) diagnosis of pancreatic serous cystadenoma (SCA) remains challenging. This retrospective study aimed to evaluate the roles of cyst fluid ancillary testing and combined fine-needle biopsy (FNB) in improving the diagnostic yield.

Methods: The authors retrospectively reviewed cytology cases that were histologically confirmed SCAs. Clinical features and FNA cyst fluid biochemical and molecular analysis results along FNB findings were reviewed.

Results: The study cohort included 31 cases from 13 male and 18 female patients with a mean age of 65. The original cytologic diagnoses were nondiagnostic (n = 6, 19%), negative for malignant cells/cyst contents (n = 7, 23%), atypical cells (n = 3, 10%), nonmucinous cyst (n = 11, 35%), and serous cystadenoma (n = 4, 13%). Cyst fluid carcinoembryonic antigen (CEA) analysis was performed in 17 cases, all of which showed a low CEA level (<192 ng/mL). All 14 cases with molecular testing showed a wild-type KRAS. Inhibin immunohistochemistry was retrospectively performed on the FNA cell blocks, inhibin was positive in six of seven cases tested. In 15 cases with concurrent FNA and FNB biopsies, the diagnosis of SCA was seen in only one FNA case (7%) but 13 FNB cases (87%).

Conclusions: This study suggests that FNA diagnosis of SCA remains challenging even with ancillary testing including cyst fluid CEA level and KRAS mutation analysis. Adjunct inhibin immunostaining may help improve the cytologic diagnosis of selective SCA cases. FNB appears superior to FNA for a definite diagnosis of SCA.