Analysis of the concordance in the EGFR pathway status between primary tumors and related metastases of colorectal cancer patients:implications for cancer therapy.

Patients with metastatic Colorectal Cancer (mCRC), in which primary tumors are KRAS mutated, have no response to anti-EGFR therapy. However, less than half of mCRC patients with KRAS wild-type primary tumors respond to anti-EGFR therapy. Other downstream effectors of the EGFR pathway are being analyzed to fine-tune KRAS predictive value. However, as the primary tumor is the tissue of analysis that determines the use of anti-EGFR therapy in advanced disease, a high concordance in the status of these effectors between primary tumors and related metastases is required. We analyzed the concordances of downstream EGFR effectors in tumoral pairs of primaries and related metastases in a series of KRAS wild-type patients. One hundred seventeen tumoral pairs from patients with CRC were tested for KRAS mutational status. The level of concordance in the presence of KRAS mutations was 91% between the primary tumor and related metastases. The 70 pairs with KRAS wild-type primary tumors were further analyzed for BRAF and PIK3CA mutational status and for EGFR, PTEN and pAKT expression, and the number of concordant pairs was 70 (100%), 66 (94%), 43 (61%), 46 (66%) and 36 (54%), respectively. Our findings suggest that the mutational status of KRAS, BRAF and PIK3CA in the primary tumor is an adequate surrogate marker of the status in the metastatic disease. On the other hand, the immunohistochemical analysis of EGFR, PTEN and pAKT showed a much higher degree of discordance between primaries and related metastases.