PET Imaging Needs Backup in Lung Cancer

[Christine]

SEOUL, South Korea, Sept. 10 -- Positron emission tomography (PET) scans can be useful for staging lung cancer but may not be sufficient alone, researchers affirmed.

In a small study, PET altered the computed tomography (CT)-based tumor stage for 44% of patients, but pathology confirmed less than half of these alterations as accurate, reported Sergio L. Faria, M.D., Ph.D., of McGill University Health Centre in Montreal, and colleagues at the International Association for the Study of Lung Cancer's world conference here.

"As has been shown, PET is better than CT to evaluate the extent of the disease, but results of PET should ideally be confirmed by pathology," Dr. Faria said.

This may come as no surprise to most oncologists, commented Andrew T. Turrisi, III, M.D., of Wayne State University in Detroit, who was a chair of the session at which the paper was presented.

"You can't use it alone," he said. "In fact, you have to use all three, and you have to use a little bit of judgment."

A previous study had shown that PET, integrated with CT, altered tumor volume delineation in about 50% of non-small-cell lung cancer cases compared with CT alone.

Dr. Faria's group went a step further to compare findings with pathology.

Their study included 32 patients with histologically-proven localized non-small-cell lung cancer with tumor tissue as well as a pre-treatment chest CT and fluorodeoxyglucose PET integrated with CT (FDG-PET/CT).

The researchers generated two sets of theoretical gross tumor volumes and tumor stages based, respectively, on CT and PET/CT without use of any mathematical algorithm. They found:

- PET altered CT-determined Tumor, Nodes, and Metastases (TNM) stage in 44% of cases (14 of 32).

- Pathology altered CT staging in 69% of cases (22 of 32).

- Pathology altered PET staging in 50% of cases (16 of 32).

- PET/CT altered tumor volume in 56% of cases (18 of 32) compared with CT.

In nearly all of the cases in which PET/CT altered tumor volume, there was at least a 30% change in volume (16 of 18).

Most of the substantial changes (10 of the 16) were an increase rather than a decrease in tumor volume.

Because PET staging was accurate by pathology more often than CT was, Dr. Faria concluded that PET was a better method.

But, "we don't know if the changes are better," he acknowledged. "Whether FDG-PET/CT-based radiation planning will improve outcome or quality of life for [non-small-cell lung cancer] patients is unknown."

Although the study sounds a cautionary note against drawing volumes or staging based on PET alone, the sense of the room at the session was that PET can be useful in conjunction with CT and pathology and that each adds slightly different information about the tumor, Dr. Turrisi concluded