Popular wisdom says the earlier a cancer is detected, the more successful the treatment and the better the chances of survival. But this does not seem to hold true for at least one kind of lung cancer, according to new research.
The surprise finding of the study, which appears in the June issue of the journal Chest, was that there was no correlation between tumor size and survival. ?It remains to be seen whether detecting smaller nodules with newer [more sensitive] technologies such as computed tomography (CT) scans will alter the natural history of the disease,? said lead investigator Edward F. Patz, M.D., of the department of radiology at Duke University Medical Center in Durham, N.C.
Patz and colleagues studied 510 consecutive patients, average age 63, who had been diagnosed with early-stage non-small cell lung cancer (which accounts for about 80 percent of all lung cancers) between 1981 and 1999. Their tumors were considered small, at 3 centimeters (a little more than an inch) or less. The patients were treated with chemotherapy or radiation.
Currently, the smallest-size nodule detectable by chest X-ray is close to 5 cm (about two inches). According to Patz, earlier preliminary trials using CT scanning showed that in up to 30 percent of cases, upon initial examination the small primary lung cancers had already spread to regional lymph nodes or distant sites.
Typically lung cancer does not cause symptoms early in the course of the disease, and there is no effective screening method.
Lung cancer is the leading cause of death from cancer in both men and women in this country, killing approximately 160,000 people annually, according to the National Cancer Institute. This year, about 177,000 new primary lung cancers will be diagnosed in the U.S. About 25 percent of patients will receive surgery in hopes of curing the disease (see a related story). The overall five-year survival rate is only 13 percent.
?Despite continued advances in diagnostic techniques, treatment protocols and [understanding of] tumor biology,? said Patz, ?the survival rate for lung cancer has shown only minimal improvement over the past several decades. Most patients still present with advanced disease, at which time therapeutic options are less than optimal.?
The point at which cancer spreads or turns aggressive has not been well defined.
But by the time a tumor has grown to 5 cm--close to the detectable range of chest X-ray--that point may already have been reached, the Duke team believes. Their findings suggest that the size of nodules does not reliably predict how the cancer will behave.
In an accompanying editorial, William C. Black, M.D., associate professor of radiology at Dartmouth Medical School in Hanover, New Hampshire, wrote that ?the unexpected observations on survival in [early-stage] lung cancer are timely and provocative. Although they can probably be explained by some combination of chance and confounding [other factors], these findings nevertheless force us to think hard about screening with CT.
?As the authors caution, we should not rush headlong into screening before its effectiveness has been demonstrated by randomized clinical trials or mathematical models that properly account for lead time [yielding an apparent increased survival due to earlier diagnosis], overdiagnosis and variations in tumor biology.?
Rasim Gucalp, M.D., a specialist in the department of oncology at Montefiore Medical Center in the Bronx, N.Y., noted that the results of the study might well have been affected by the small number of patients analyzed. In addition, he said, the age range is very large and the causes of deaths were not listed as cancer-specific, so, for example, older smokers in the study may well have died of heart disease rather than lung cancer.
Gucalp added that several large international studies are under way to examine whether there is a difference in outcome if people are screened by chest X-rays or low-dose CT scans. The cost-effectiveness of using the more sensitive CT called helical CT, which can detect even smaller tumors, for screening is also being investigated. A 1999 study published in The Lancet found that helical CT increased detection of small lung tumors?many under one centimeter in size--fourfold over chest X-rays, but whether this will result in a survival advantage remains to be seen.
Gucalp said he expects the cost of CT screening in general to decrease over time, much as that of mammography did.
So what may have an impact on lung cancer survival?
?As more is understood about the biology of lung cancer, it seems that an integration of imaging findings, molecular characteristics of the tumor and host response to this malignancy will be necessary,? concluded the authors.
The Duke research team advises against routine widespread use of early-detection methods until more appropriate prospective randomized trials are completed.
