Diagnosing Cancer Made Easy

Detecting some tumors may become a lot simpler and less invasive in the future, according to a study published in the 17 March issue of Science. Researchers have shown how certain mutations in DNA found in bodily fluids can help doctors detect cancer of the bladder, lung, and neck and head.

The telltale mutations showed up in the mitochondria, the powerhouses within the cell, which each have many copies of a minigenome. Like nuclear DNA, this mitochondrial DNA (mtDNA) can accumulate mutations. Three years ago, researchers found several unique mutations in mtDNA from bowel tumor cells. It's not clear exactly what causes them, or what role they play in cancer. But the finding spurred molecular geneticist David Sidransky and colleagues at the Johns Hopkins University in Baltimore to look for mtDNA mutations that might flag other types of cancer.

The team took tumor cells from 46 patients with cancer of the bladder, head, neck, and lung and sequenced the cells' mtDNA. Comparing the sequences with those from blood samples and healthy tissue from the same patients, they found 39 mutations specific for the tumor cells. Sidransky's team suspected that because cellular debris from the bladder sometimes ends up in urine, they might look for the mtDNA mutation there as well; likewise, mutations from neck and head tumors might show up in saliva, and from lung tumors in lung fluid.

Sure enough, when the researchers analyzed these body fluids, they found the same characteristic mutations as those that turned up in the mitochondria from tumor tissues. Because mitochondria contain so many copies of the same DNA, the mutations were also more abundant than known tumor-associated mutations in nuclear DNA, and thus easier to detect.

The technique may be a useful and patient-friendly addition to the growing arsenal of genetic tests to detect cancer, says Curtis Harris, a molecular epidemiologist with the National Cancer Institute in Bethesda, Maryland.