Chest x-rays are a powerful diagnostic tool in detecting early lung cancer, but they also have a big drawback in that they generate a high number of false positive test results and additional extra testing, according to a new study by the National Cancer Institute (NCI).
The research took place from 1993 to 2001, as PLCO - Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial - investigators enrolled 154,942 men and women between the ages of 55 to 74 years of age. These participants included current and former smokers, as well as individuals who never smoked. These findings are based on an analysis of the trial participants' initial chest X-rays.
"There is no accepted early screening technique for lung cancer," said Christine Berg, MD, the NCI investigator who leads the PLCO trial, in a release. "The PLCO trial will show if chest x-rays, by catching lung cancer when it is still operable, can reduce the death rate from lung cancer."
Upon analysis of the results from the 67,038 men and women who received a baseline chest x-ray, 8.9 percent showed abnormal results and were sent for additional exams. After further review, 126 (2.1 percent) were diagnosed with lung cancer within a year of the original exam.
"The positive predictive value was low," said Berg. "That means there were a lot of false positives on the initial x-rays. If you get a positive result from a chest x-ray, the message is 'don't panic.'" Berg added that tissue variations and other benign factors can resemble tumors on an x-ray, thus leading to false positives.
One of the key goals of the trial is to determine whether chest x-rays can reduce lung cancer mortality in men and women 55 to 74 years of age. Additionally, the analysis indicated what was already known: smoking vastly increases the risk for lung cancer. Of current smokers in the trial, 6.3 people per 1,000 screened came back positive; former smokers - defined as those who quit for less than 15 years - the rate of detection rate was 4.9 per 1,000; and for non-smokers, lung cancer was diagnosed in 0.4 individuals per 1,000, according to the study.
The study is additionally important because catching lung cancer early is vital, and improves survival substantially, with 70 percent of patients who are diagnosed early more likely to survive at least five years.
This report appeared in the Dec. 21, 2005 issue of the Journal of the National Cancer Institute.