Tiny RNA Molecules Control Breast Cancer's Spread

(Page 2)

If patients with more ominous cancers can be identified, doctors can then focus on administering more aggressive therapies from the start.

Most deaths from cancer occur after a tumor has metastasized or spread to other parts of the body.

"Metastasis is the overwhelming cause of death of patients that we see from cancer," confirmed study author Dr. Sohail F. Tavazoie, a postdoctoral fellow in the oncology-hematology fellowship program at Sloan-Kettering, in New York City.

But why are some cancers prone to spread while others are not?

Part of the answer lies in microRNAs, which subdue the activity of sets of genes linked to metastasis.

DNA is made up two strands (a double helix) of "letters" that contain all the information needed to create cells. RNAs are single-stranded copies of segments of the DNA, Tavazoie explained. While many RNAs are translated into proteins, others (including microRNAs) have the power to shut off genes.

The microRNAs appear to act as master "supervisor" or regulator of these sets of genes.

Tavazoie hypothesized that some of these microRNAs are missing in more dangerous cancers. "The brakes are lifted, so a group of genes could actually be activated," he explained.

Tavazoie and his colleagues, who published their findings in the Jan. 10 issue of Nature, investigated how microRNAs might play a role in controlling the expression of genes that in turn control metastases.

First, they compared microRNAs produced by metastatic human cancerous cells with those produced by non-metastatic cancer cells in the laboratory.

"We saw that the highly metastatic cancer cells had lost some of these small RNA molecules," Tavazoie said.

Could some of these molecules be the so-called supervisors of other genes involved in cancer becoming lethal?

In fact, when three of eight microRNAs identified were put back into aggressive cells, those cells backed down, becoming less likely to spread. These experiments were done in mice programmed with human cancer cells.

The researchers then took the project a step further, predicting that women with breast cancer who had lost these small RNA molecules would be more likely to have an aggressive form of cancer.