Detection of Intracellular Cytokeratin 20 in CD14dim Monocytes: A Potential Tool for the Screening of Colorectal Adenocarcinoma in Peripheral Blood

Abstract

Cancer is among the leading causes of death worldwide. Early and accurate detection is essential as it can effectively attenuate the dismal prognosis of this disease. Current screening/detection techniques are limited by issues of sensitivity and specificity, in addition to low compliance rates related to their invasive nature. However, the detection of intracellular biomarkers in the blood that are specific for carcinoma has the potential to address this challenge. In this study, we exploited our knowledge of interactions within the tumor microenvironment to identify a potential biomarker for carcinoma. Specifically, we investigated the role of monocytes in relation to lung and colorectal carcinoma (CRC). We hypothesized that since phagocytosis is a major responsibility of monocytes, tumor fragments could be found in the vacuoles of their cytoplasm. Additionally, we hypothesized that while most monocytes transform into macrophages once in the tissue, a small portion of them may retain monocyte character and return to the circulation after having contact with tumor cells. We proposed to utilize a combination of immunofluorescence techniques and multi-parameter flow cytometry to test our hypotheses. Given that monocytes are a heterogeneous group of cells categorized into 3 main subsets, each with distinct functions and phenotypes, we performed a monocyte phenotyping experiment to study the quantitative distribution of these subsets in the context of cancer. We found that non-classical/patrolling monocytes (CD14dimCD16+) are significantly elevated in both lung and colorectal cancer (CRC) patients relative to healthy controls. We also found that the percentage of CD14dim monocytes is elevated in lung adenocarcinoma patients prior to tumor resection, but significantly diminished immediately following surgery to remove the tumor. Perhaps most remarkably, we discovered that cytokeratin 20 (CK20) is detectable intracellularly in the CD14dim monocytes of colorectal adenocarcinoma patients and to a significantly higher extent compared to controls. Although preliminary, these findings suggest that intracellular CK20 in CD14dim monocytes in peripheral blood has the potential to serve as a novel screening tool for the early detection of colorectal cancer.