Bax expression decreases significantly from primary tumor to metastasis in colorectal cancer

Bax is a proapoptotic member of the bcl-2 family. Previous studies about Bax have shown that the expression increases from normal to tumor tissue, but the clinical significance is contradictory. Our aims were to analyze the expression of Bax from normal mucosa to primary tumor and to metastases in colorectal cancer patient. We further investigated whether low Bax expression in the primary tumor or changed expression from normal mucosa to primary tumor and to metastases had biologic and clinical significance.

The study included 135 patients with primary colorectal adenocarcinoma, of whom 31 had metastases in the lymph nodes and 75 had normal mucosa. Immunohistochemistry, DNA sequencing, and microsatellite analysis were used to detect Bax expression, mutations, and microsatellite instability.

The protein was observed in 132 of 135 tumors, all normal epithelial cells and metastases. The frequencies of weak expression were greater from well/moderately to poorly differentiated and to mucinous carcinomas. Bax expression was stronger from normal to tumor tissue, but subsequently decreased in metastases. The matched cases with lower expression in the metastases than in the primary tumor showed a more infiltrative growth pattern and more distal metastases.

The association of Bax expression with tumor differentiation/histologic types and a decreased expression in the metastases, suggests that Bax expression may be involved in tumor differentiation/histologic types and metastatic progression. We also propose the novel notion that changed Bax expression in the metastases compared with the primary tumors might provide information to determine the clinicopathologic characteristics of the tumor.