Evaluation of PD-L1 protein expression in circulating tumor cells (CTCs) of patients with rectal cancer

Abstract

Colorectal cancer (CRC) is the third most frequently diagnosed in the world and the second largest cause of cancer death. In Brazil, 36 mil cases were diagnosed in men and the second in women. Among these numbers, in Brazil, 17.284 deaths were recorded for CRC, of which 4.968 were for rectal cancer. A major risk factor for tumor progression is the spread of tumor cells in the blood. Circulating tumor cells (CTCs) are one of the mechanisms of cancer spread, they can circulate in the blood for months or even years before the development of metastases. It is this spontaneous circulating of CTCs that also defines the invasive behavior of tumor. Generally undetectable by histopathological analyses and by high resolution exams, more sensitive tests such as immunocytochemical and molecular assays have been developed and have been allowing the detection of CTCs in several types of materials. Many studies have now focused on analyzing the protein expression of CTCs in search of invasion and resistance markers that can predict treatment outcomes. An important marker of cancer resistance is the PD-L1 membrane glycoprotein (programmed death ligand 1), which is an important component in the cancer immunity cycle, performing the function of preventing the immune system from destroying cancer cells. Its expression may predict a favorable prognosis for treatment with anti-PD-1 therapy. This will be a retrospective study, where XX blood samples from patients with rectal cancer will be analyzed at two different times, before beginning and after the end of neoadjuvant chemoradiotherapy. Our main objective is to evaluate the protein expression of PD-L1 in the peripheral blood of patients with locally advanced rectal cancer and to correlate this expression with clinical tumor evolution, global survival and progression free.