Guanylyl cyclase C (GCC) is expressed exclusively in normal intestinal mucosal cells, primary and metastatic
colorectal cancers (CRC). The aim of this study was to determine the possible association between the GCC expressions in peripheral blood, prognostic parameters and response to
chemotherapy in CRC patients. Fourty-nine metastatic CRC patients and 41 healthy controls with similar age and sex were included to this study. Peripheral blood GCC expressions are measured by the
reverse transcriptase-polymerase chain reaction (RT-PCR) method. Interstingly, no GCC expression was measured in healthy controls but GCC expressions of the patients were detectable. Although there was a significant reduction in GCC expressions in 30 patients with regression (from 5.46 ± 4.12 to 0.06 ± 0.03, p < 0.0001), marked increase in GCC expressions was observed in 19 patients with progression following
chemotherapy (from 0.43 ± 0.19 to 1.38 ± 0.52, p = 0.0174). Significant correlation was found between the GCC expressions and
carbohydrate antigen 19-9 (CA19-9) levels (p = 0.0041) in 30 patients with regression before
chemotherapy. Marked correlation was also detected between the GCC expressions and
carcinoembryonic antigen (CEA) levels (p = 0.0072) in 19 patients with progression before
chemotherapy. The results of the present study suggest that peripheral blood GCC expressions along with CEA and CA19-9 can be used to determine the early respose to
chemotherapy in patients with metastatic CRC. These findings imply that higher expression of GCC in peripheral blood seems to be an
indicator of good therapeutic response to
chemotherapy and remission. Monitoring the peripheral blood GCC expressions may allow employing different treatment options to metastatic CRC patients.