Circulating tumor cells as a possible marker for micrometastatic disease in patients with localized pancreatic cancer.

Abstract

175 Background: Circulating tumor cells (CTCs) are cells shed into circulation from tumors. They are increasingly recognized to be important biomarkers of disease burden in patients with solid tumors. Studies in pancreatic ductal adenocarcinoma (PDAC) have been limited due in part to low sensitivity of existing assays with extremely low numbers detected (0-15 per 7.5-15ml of blood). The development of newer microfluidic platforms has resulted in the ability to detect substantially greater numbers of CTCs. Methods: 15 patients with PDAC were enrolled in an IRB-approved study. Blood was collected in EDTA tubes and processed within 3 hours. CTCs were selected from 2-3ml of whole blood using monoclonal antibodies against epithelial cell adhesion molecule (EpCAM) and enumerated using a novel microfluidic platform. CTCs were confirmed by DAPI, CK8/18/19 and CD45 staining. Results: Patients with metastatic disease (n=12) had a mean of 29.7, median of 22 (3.5-107) CTCs per 1ml of blood. Patients with localized disease (n=3) had a mean of 3.8, median of 2.9 (2.3-6.2) CTCs per 1ml of blood. 0.5-1 CTCs per 1ml were detected in normal controls (n=2). The number of CTCs was significantly different between localized, metastatic and normal patients (p=0.01). 1 patient, initially thought to have localized disease by standard imaging but found to be metastatic at time of operation, had a mean of 45.9 CTCs per 1ml of blood compared to a mean of 3.8 CTCs per 1ml in patients who underwent a curative resection (p=0.009). Conclusions: Studies of CTCs in PDAC have been very limited. Our ability to detect large numbers of CTCs with good dynamic range suggests that further investigation into CTCs as a prognostic marker in PDAC is warranted. This is the first study that we are aware of to find CTCs in patients with localized disease. The presence of CTCs in patients with localized PDAC is surprising and may be associated with findings of unexpected metastatic disease at surgery. Further follow-up will be needed to determine if the presence of CTCs in these patients is a harbinger of shorter progression-free survival and overall survival after curative operations.