Tumor heterogeneity predicts metastatic potential in colorectal cancer

Purpose: Tumors continuously evolve to maintain growth; secondary mutations facilitate this process, resulting in high tumor heterogeneity. In this study, we compared mutations in paired primary and metastatic colorectal cancer (CRC) tumor samples to determine whether tumor heterogeneity can predict tumor metastasis. Experimental design: Somatic variations in 46 pairs of matched primary-liver metastatic tumors and 42 primary tumors without metastasis were analyzed by whole exome sequencing. Tumor clonality was estimated from single nucleotide and copy number variations. The correlation between clinical parameters of patients and clonal heterogeneity in liver metastasis was evaluated. Results: Tumor heterogeneity across CRC samples was highly variable; however, a high degree of tumor heterogeneity was associated with a worse disease free survival. Highly heterogeneous primary CRC was correlated with a higher rate of liver metastasis. Recurrent somatic mutations in APC, TP53, and KRAS were frequently detected in highly heterogeneous CRC. The variant allele frequency of these mutations was high, while somatic mutations in other genes such as PIK3CA and NOTCH1 were low. The number and distribution of primary CRC sub-clones were preserved in metastatic tumors. Conclusions: Heterogeneity of primary CRC tumors can predict the potential for liver metastasis and thus, clinical outcome of patients.

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