Detection of KRAS Oncogene in Peripheral Blood as a Predictor of the Response to Cetuximab Plus Chemotherapy in Patients with Metastatic Colorectal Cancer

Abstract

Purpose: Previously we developed membrane-arrays as a promising tool to detect circulating tumor cells (CTC) with KRAS oncogene in patients with malignancies.This study was conducted to determinate the predictive values of CTCs with KARS mutation by membrane-arrays for metastatic colorectal cancer patients treated with cetuximab plus chemotherapy. Experimental Design: Seventy-six metastatic colorectal cancer patients receiving cetuximab plus FOLFIRI or FOLFOX-4 chemotherapy were enrolled. KRAS mutation status in the peripheral blood of these patients was analyzed using membrane-arrays, and KRAS mutation status in tumors was analyzed by DNA sequencing. Results: Among 76 metastatic colorectal cancer patients, KRAS mutations in tumors and in peripheral blood were identified in 33 (43.4%) and 30 (39.5%) patients, respectively.The detection sensitivity, specificity, and accuracy of membrane-arrays for CTCs with KRAS oncogene were 84.4%, 95.3%, and 90.8%, respectively, and indeed a highly significant correlation to KRAS mutations in tumors (P < 0.0001) was observed. Forty-five (59.2%) patients responded to cetuximab plus chemotherapy, and 41 and 40 were wild-type KRAS in tumors and peripheral blood, respectively (both P < 0.0001). Patients with tumors that harbor wild-type KRAS are more likely to have a better progression-free survival and overall survival when treated with cetuximab plus chemotherapy (P < 0.0001). Likewise, patients with CTCs of wild-type KRAS in peripheral blood express a better progression-free survival and overall survival when treated with cetuximab plus chemotherapy (P < 0.0001). Conclusions: These findings provide evidence that detection of KRAS mutational status in CTCs, by gene expression array, has potential for clinical application in selecting metastatic colorectal cancer patients most likely to benefit from cetuximab therapy.Colorectal cancer is the second leading cause of cancer-related death in western countries and is the third major cause of cancerrelated death in Taiwan, with >9,000 new cases and 4,000 deaths per year. 12 In the past decade, significant improvements have been made in response rates, progression-free survival (PFS), and overall survival (OS) of metastatic colorectal cancer patients (1 -4). This prominent improvement is mainly due to the recent introduction of new combinations of standard chemotherapy, including 5-fluorouracil/folinic acid, irinotecan, and oxaliplatin, and to the new therapeutic agents targeting molecular events involved in colorectal carcinogenesis such as monoclonal antibodies (mAb) against epidermal growth factor receptor (EGFR) or mAbs against vascular endothelial growth factor. Previous studies (5 -11) showed that the benefits of the anti-EGFR mAb cetuximab among patients with metastatic colorectal cancer are limited to those who have colorectal tumor tissues with wild-type KRAS genes, and KRAS genes with mutations are 12

Circulating tumor cells

“…27 Few studies have explored in small series of mCRC patients the correlation between KRAS mutational status in primary or metastatic tumor and in CTCs, revealing further mutational discordance, possibly complicating the selection of patients candidate for anti-EGFR treatments. [28][29][30][31][32][33] Our results confirm a divergent KRAS status in a large proportion of cases, highlighting that KRAS wild-type CTCs are frequently detected in peripheral blood of patients harboring mutated primary tumors. As potential mechanism to explain the relative prevalence of wild type KRAS CTCs, 34 the generation of hypoxia in large advanced tumors or induced by treatments has been evoked.…”

Detection of KRAS mutations in circulating tumor cells from patients with metastatic colorectal cancer

“…1 In addition, initial primary tumor specimens are not always representative of the metastasis that can occur many years after the resection of the primary tumor. 2 After primary tumor biopsy or surgical removal, many other mutations can be acquired and other specific abnormalities found in the primary tumor can be lost. In this way, the CTC analysis can provide a non-invasive way of evaluating a tumor genotype and better correlate with the dynamic process of tumor progression and resistance to chemotherapeutic drugs.…”

Oncogenic mutations as predictive factors in colorectal cancer

“…Some authors have shown that detection of KRAS mutations in the peripheral blood of mCRC patients is possible by the development of combining tests indicating in blood, first the presence of tumour DNA (circulating tumours cells), then KRAS status, with a highly significant correlation to KRAS mutations in tumours (Di Fiore et al, 2008;Yen et al, 2009). Moreover, it was reported in a series of 76 patients that those with KRAS wild-type circulating tumour cells had a better progression-free and overall survival when treated with cetuximab plus chemotherapy (Po0.0001) (Yen et al, 2009). These findings encourage to collect blood samples of mCRC patients to validate the clinical relevance of KRAS mutation detection in blood in future clinical trials with anti-EGFR monoclonal antibodies.…”