Peripheral blood monocyte counts are elevated in the pre-diagnostic phase of pancreatic cancer: A population based study

Background: Early diagnosis of pancreatic ductal adenocarcinoma (PDAC) is associated with improved outcomes. A biomarker with incremental change in the pre-diagnostic phase of the disease would be valuable for early detection. In our clinical experience, we have observed elevated peripheral blood monocyte (PBM) counts in PDAC patients at diagnosis. In this study, we aimed to compare PBM counts in PDAC cases and healthy controls at diagnosis and in the 2-year pre-diagnostic period. Methods: Using the Rochester Epidemiology Project database, we identified all patients diagnosed with PDAC between 2000 and 2015 (n = 219) and age-and gender-matched disease-free controls (n = 438). PBM counts and temporal trends were analyzed over a 24 month period before PDAC diagnosis. The groups were compared using Fisher's exact test and t-test. Results: At diagnosis, compared to controls PDAC cases more often had monocytosis (23% vs 8%; p < 0.001) and higher mean PBM count (x10⁹/L) (0.73 vs 0.59; p < 0.001). In the 2-year pre-diagnostic period, mean PBM counts were significantly higher in PDAC cases in the interval from 6 months to diagnosis (0.69 vs 0.61; p = 0.03). PDAC cases with monocytosis at diagnosis had a significantly lower median survival (1.9 months vs. 7.6 months; p = 0.001). Conclusion: Monocytosis is more prevalent in PDAC patients at diagnosis compared to controls and is associated with lower median survival. In a subset of patients, PBM count elevation precedes PDAC diagnosis by 6 months. This novel observation can possibly augment strategies for early diagnosis of PDAC but needs further study.