MEDICATIONS: PET SCANS ACCURATE FOR IDENTIFYING MALIGNANT LUNG LESIONS

February 21, 2001 — Positron emission tomography (PET) is an accurate noninvasive imaging test for diagnosis of pulmonary nodules and larger mass lesions, although few data exist for nodules smaller than 1 cm. in diameter, according to an article in the February 21, 2001, issue of The Journal of the American Medical Association.

Michael K. Gould, M.D., M.S., of the Veterans Affairs Palo Alto Health Care System, Palo Alto, Calif., and colleagues conducted a meta-analysis of studies published between January 1966 and September 2000 to estimate the diagnostic accuracy of PET (using a radioactive tracer called 18-fluorodeoxyglucose [FDG]) for identifying malignant focal pulmonary lesions. The studies enrolled at least ten participants with pulmonary nodules or masses, included at least five participants with malignant lesions, and presented sufficient data to permit calculation of sensitivity and specificity.

According to background information cited in the study, focal pulmonary lesions may be classified as nodules or masses, depending on their size. Pulmonary nodules are lesions in the lung that measure less than 3 to 4 cm. in diameter and are completely surrounded by aerated lung. Most nodules are asymptomatic, and approximately half prove to be malignant. Pulmonary masses measure more than 3 to 4 cm. in diameter, often cause symptoms, and are even more likely to be malignant. Diagnostic evaluation of focal pulmonary lesions should be both accurate and efficient to facilitate prompt treatment of malignant tumors.

For the meta-analysis, two reviewers independently assessed study quality and abstracted data regarding prevalence of malignancy and sensitivity and specificity of the PET test. The authors report that 40 studies met inclusion criteria, but study methodological quality was fair, sample sizes were small, and blinding was often incomplete.

"For 1,474 focal pulmonary lesions of any size, the sensitivity of FDG-PET for detecting malignancy ranged from 83 percent to 100 percent," they write.

Specificity was extremely variable. "The mean sensitivity and specificity were 96.0 percent and 73.5 percent, and the median sensitivity and specificity were 97.0 percent and 77.8 percent, respectively," the authors write. "For 450 pulmonary nodules, the mean sensitivity and specificity of FDG-PET for detecting malignancy were 93.9 percent and 85.8 percent, and the median sensitivity and specificity were 98.0 percent and 83.3 percent, respectively."

"We identified only 8 instances in which results were specified for nodules measuring less than 1 cm. in diameter, including 3 true-positive cases, 2 true-negative cases, and 3 false-negative cases," the authors write.

The authors believe their study addresses two important clinical issues related to metabolic imaging with FDG. "First, we failed to show that semiquantitative image interpretation improves the accuracy of FDG-PET. Second, we found no evidence that FDG-PET is more accurate than metabolic imaging with FDG and a modified gamma camera," they write.

"Policy-level decisions regarding dissemination of FDG-PET must consider not only diagnostic accuracy but also clinical outcomes and costs," the authors suggest. "At present, Medicare reimbursement for FDG-PET imaging is approximately $1,912. In comparison, reimbursement for non-contrast CT of the thorax is $276 and reimbursement for CT-guided needle biopsy is approximately $560."

"Formal cost-effectiveness studies are needed to determine if diagnostic strategies that include FDG-PET represent a good value for the health care dollar," they conclude.

In an accompanying editorial, Ethan Balk, M.D., M.P.H., and Joseph Lau, M.D., of the New England Medical Center, Boston, point to the need to evaluate PET scans and other promising emerging technologies.

"After safety considerations, the basic issue in the evaluation of any new diagnostic technology focuses on the test performance, typically measured as the sensitivity and specificity. Although numerous studies have been published on diagnostic technologies, many do not truly evaluate diagnostic performance, provide no useful information, or are of poor methodological quality," they write.

"To allow meaningful evaluation of PET (and other diagnostic tests), researchers should ensure that their study questions are clear and precise and that the study population, condition of interest, intervention and outcome are all well-defined," they continue. "To determine the proper role of the new technology and to appreciate incremental benefits (i.e., whether PET should replace CT and MRI or be used in addition to CT and MRI), studies explicitly addressing these questions need to be performed."

Drs. Balk and Lau point out that proponents of new technologies often speculate that their widespread deployment could lead to reduced health care costs. "It remains to be determined whether use of PET could avoid unnecessary procedures in some patients and, thus, result in overall net savings," they write. "However, this must be proven rather than assumed, and well-designed clinical trials must be conducted to assess this hypothesis."

"To be of value, methodologically rigorous studies must be conducted to address the important questions. Given the billions of dollars at stake and the need to ensure that patients will truly benefit from expensive new technologies, the costs of properly performing methodologically sound clinical studies seem minuscule," they conclude.