March 13 (HealthDay News) -- Certain genetic alterations in tumors and tissue from patients with early-stage lung cancer may identify those at greatest risk for cancer recurrence, say researchers at the Johns Hopkins Kimmel Cancer Center.

They said the finding could alter the treatment approach for lung cancers, which recur within five years in 30 percent to 40 percent of patients.

"This is DNA forensics for cancer. While there may be no trace of cancer that we can spot after surgery with a microscope, the DNA evidence from these tumors may have been left at the scene, especially in lymph nodes," Dr. Malcolm Brock, an associate professor of surgery at Johns Hopkins, said in a prepared statement.

He and his colleagues analyzed more than 700 surgical samples from 167 patients with early-stage, non-small cell lung cancer (51 whose cancer recurred within 40 months and 116 whose cancer did not recur) to identify specific methylation patterns associated with lung cancer.

In methylation, chemicals known as methyl groups attach to the DNA ladder structure of a gene, which can cause problems that lead to the development or recurrence of cancer. Of seven genes known to be linked to lung cancer, four of them -- p16, H-cadherin, APC and RASSF1A -- showed the highest amounts of methylation in patients with recurrent lung cancer.

Many of the genes showed a twofold difference in methyl marks between recurrent cancer and non-recurrent cancer, the study found.

"The DNA evidence we see for many of the recurring cases suggests it may be wise if our work is confirmed to reclassify such cancers as advanced disease instead of early-stage," Brock said.

He and his team also found lung cancer returned more quickly than average among 11 patients with higher than normal methylation in two genes -- p16 and H-cadherin -- located in both tumor tissue and a lymph node distant from the original tumor site. In eight of the 11 patients, lung cancer recurred within a year, and recurred in the remaining three patients within 30 months.

The study was published in the March 13 issue of the New England Journal of Medicine.

SOURCE: Johns Hopkins Medicine, news release, March 12, 2008