Abstract A64: Peripheral blood monocytes predict survival in pancreatic cancer.
Authors: Sanford Dominic E. , Belt Brian A. , Panni Roheena Z. , Mitchem Jonathan B. , Denardo David G. , Goedegebuure S. Peter , Linehan David C. 
Published: August 2014

Background: Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy with a 5-year survival of &lt; 5%, and a mortality rate nearly equal to its incidence. Characteristic of this tumor is a microenvironment in which monocytes/macrophages are abundant. Human monocytes are divided into two major subsets: inflammatory (IM) and resident (RM) monocytes. IM make up 85%-90% of human peripheral blood monocytes, and are identified by the expression of CD14 and CCR2. The CCL2-CCR2 chemokine axis is a crucial signaling pathway in physiologic IM recruitment from the bone marrow under inflammatory conditions. Within the tumor microenvironment, IM can differentiate into tumor associated-macrophages (TAM) which are immunosuppressive, and directly promote tumor progression by enhancing angiogenesis, growth, and invasion. We present evidence that IM are recruited from the bone marrow to the peripheral blood and tumors of PDAC patients. Furthermore, we hypothesize that that peripheral blood monocyte count is predictive of patient survival in PDAC.

Methods: PDAC tumor specimens (n=11) and normal pancreas (n=10) were subjected to flow cytometry and RT-PCR. Flow cytometry was performed on the peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC) of PDAC patients (n=13) and compared to healthy controls (n=11). For the survival analysis, 483 patients with PDAC underwent pancreaticoduodenectomy between 1997 and 2011 at a single institution. We excluded 110 patients with pre-operative leukocytosis (WBC&gt;11,000 cell/ul) or who died within 30 days of surgery. We stratified the remaining 373 patients into 3 groups based on the prevalence of monocytes in peripheral blood leukocytes using their pre-operative CBC: low(&lt;6%)[n=47], mid(≥6% to &lt;11%)[n=271], and high(≥11%)[n=55] %monocyte groups. We used standard Kaplan-Meier survival statistics to compare overall survival between the three groups.

Results: PDAC tumors are infiltrated by CCR2+ cells of monocyte lineage (CD45+, CD11b+, HLA-DR+, CD115+, CD14+) [37.9% ±1.6% of CD45+ cells], and these tumors expressed significantly more CCL2 relative to normal pancreas[p&lt;0.01]. IM (CD45+, CD11b+, HLA-DR+, CD14+, CCR2+, CD16-, CX3CR1 low) were significantly more prevalent in the PBMC of PDAC patients compared to controls [10.8%±1.1% vs 5.7%±1.1% of CD45+ cells; p&lt;0.005]; whereas, resident monocytes (CD45+, CD11b+, HLA-DR+, CD16+, CX3CR1 high, CD14 low, CCR2-) were not significantly different [0.67% ±0.1% vs 0.72% ±0.1%; p=0.76]. However, IM were significantly decreased in the bone marrow of PDAC patients compared to healthy controls [10.4% ±1.1 vs 14.9 ±1.2%; p&lt;0.01]. This suggests that the mechanism of increased IM in the peripheral blood of PDAC patients is mobilization from the bone marrow. Survival analysis of PDAC patients revealed that patients in the low %monocyte group survived significantly longer than patients in the high %monocyte group (27.8 months vs 18.2 months; p=0.02 on log-rank test). Also, there was a statistically significant incremental decrease in survival from the low to mid to high %monocyte groups (p=0.01 on log-rank test for trend).

Conclusion: IM are recruited from the bone marrow to the tumor microenvironment in PDAC through the CCL2/CCR2 chemokine axis, and the prevalence of peripheral blood monocytes correlates with decreased patient survival. Developing effective intervention strategies to thwart monocyte recruitment may hold significant promise in this disease.

Citation Format: Dominic E. Sanford, Brian A. Belt, Roheena Z. Panni, Jonathan B. Mitchem, David G. Denardo, S. Peter Goedegebuure, David C. Linehan. Peripheral blood monocytes predict survival in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr A64.