Scientists have found that small strings of microRNA that are different in colon cancers can predict poor survival and poor outcomes after treatment.
In cells, the DNA in genes works by sending signals via RNA to tell the cells to make the proteins that are the workhorses of cellular activity. MicroRNA is a tiny piece of RNA which cannot produce proteins itself, but can bind to a larger messenger RNA molecule to decrease its protein-producing activity.
The research team began by looking for patterns of microRNA in colon tumors that were different from those in normal tissue nearby the cancer. They found 37 miRNA’s with a different expression in the colon tumors of 84 US patients. They then looked for associations between miRNA’s and staging, survival, and response to chemotherapy.
Then they validated the associations with another group of 113 Chinese patients in Hong Kong, focusing on five specific microRNA’s. In particular, they found one — miR-21 — that predicted both poor survival and poor response to treatment, even when other factors such as cancer stage were considered.
At five years, the percentage of US patients who had not died of cancer (cancer-specific survival) was 57.5 percent. For the Chinese patients, cancer-specific survival five years later was 49.5 percent.
However, patients with high expression of miR-21 were two and a half times as likely to die from cancer as those with lower levels. For Chinese patients, the risk was just slightly less — 2.4 times.
Both sets of patients did poorly on chemotherapy if they showed higher expression of miR-21.
Aaron Schetter PhD, MPH and colleagues in the United States and Hong Kong concluded,
Expression patterns of microRNAs are systematically altered in colon adenocarcinomas. High miR-21 expression is associated with poor survival and poor therapeutic outcome.
SOURCE: Schetter et al., Journal of the American Medical Association, Volume 299, Number 4, January 30, 2008.
A story about microRNA’s and colon cancer is on the National Cancer Institute website.
