Clinical significance of immunocytochemical staining for peritoneal lavage cytology in pancreatic cancer

Peritoneal lavage cytology for pancreatic ductal adenocarcinoma is conducted with both an intraoperative rapid diagnosis by Papanicolaou staining (cytology-rapid) and a final diagnosis by immunocytochemical staining at a later date (cytology-final) in our hospital. However, the clinical significance of cytology-final has not yet been elucidated.A total of 675 pancreatic ductal adenocarcinoma patients who underwent pancreatectomy and cytology between 2002 and 2018 were retrospectively reviewed. Diagnostic results of cytology-rapid and cytology-final and survival outcomes were analyzed.A total of 43 patients (6.4%) were diagnosed as cytology-rapid (+), and all of them were ultimately diagnosed as cytology-final (+). Among the 632 patients with cytology-rapid (-), 19 (3.0%) were eventually diagnosed as cytology-final (+). The overall survival of patients with cytology-rapid (+) and that of patients with cytology-rapid (-) did not differ to a statistically significant extent (median survival time 26.4 vs 32.9 months; P = .106). In contrast, the overall survival of patients who were diagnosed as a false-negative result by cytology-rapid was significantly worse than that of patients diagnosed as a true negative (18.7 vs 34.8 months; P = .031). The overall survival of patients with cytology-final (+) was significantly worse than that of patients with cytology-final (-) (23.6 vs 34.8 months; P = .012). A multivariate analysis showed that cytology-final (+) was an independent prognostic factor for the OS (hazard ratio = 1.43; P = .049), whereas cytology-rapid (+) was not.Immunocytochemical staining may be a useful complement to a diagnosis of cytology by conventional Papanicolaou staining in pancreatic ductal adenocarcinoma patients.