Whole-Body PET/CT Colonography Promising for Colon Cancer Staging

ESSEN, Germany, Dec. 5 -- For colorectal cancer patients, whole-body PET/CT colonography provides a one-stop tumor staging that seemed at least equivalent to CT plus PET, according to a preliminary report.

Staging of colorectal cancer patients often requires a multimodality, multistep imaging approach with additional imaging procedures to assess potential metastatic spread, said Gerald Antoch, M.D., of University Hospital Essen here, and colleagues.

PET/CT colonography, which provides whole-body staging in a single session, proved to be a "feasible" alternative, the German team reported in the Dec. 6 issue of the Journal of the American Medical Association.

In a prospective study, 47 patients enrolled from 2004 to 2006 with clinical findings and optical colonoscopy that suggested primary colorectal cancer were evaluated with whole-body PET/CT.

These findings were compared with the staging accuracy of CT followed by PET (CT+Pet) and CT alone. The patients (mean age 71; range 47-92 years) were scanned one day after colonoscopy. The study was conducted at a university hospital with a mean follow-up of 447 days.

Of the 47 patients with a total of 50 lesions, the TNM stage was correctly determined for 37 lesions with PET/CT (74%; 95% confidence interval, 60%-85%), compared with 32 lesions with CT+PET (64%; CI, 49%-77%), and 26 lesions with CT alone with a 0.7-cm node threshold (52%; CI, 37%-66%), the researchers reported.

Compared with optimized abdominal CT staging alone, PET/CT was significantly more accurate in defining TNM stage (difference, 22%; CI, 9%-36%; P=.003), which was based mainly on a more accurate definition of the T-stage.

N-stage differences were not detected between PET/CT and CT alone with a threshold of 0.7 cm for malignant nodes but were detected with a threshold of 1 cm.

There were no statistically significant differences when comparing the M-stage separately or when comparing accuracy of PET/CT with CT+PET, the researchers reported.

Of the 47 patients, whole-body PET/CT changed consecutive therapy decisions for four patients (9%; CI, 2.4%-20.4%), compared with CT alone (optimized abdominal CT, CT of the thorax) and colonoscopy.

The change in patient management was based either on a more accurate assessment of the tumor stage or on concomitant findings on PET/CT. No comparisons of therapy changes for PET/CT versus CT + PET were made, the researchers noted.

For example, in one patient PET/CT was able to distinguish between liver metastases and a secondary tumor within the liver. In another patient, PET/CT correctly classified a suspected residual tumor as scar tissue. In still another patient, a small hepatic metastasis in a patient with only one other metastasis was missed on optimized CT. The PET/CT finding altered therapy to include more extended surgery.

There are some limitations to the whole-body PET/CT technique, Dr. Antoch said. In this preliminary study, one flat adenoma was missed because of limited spatial resolution of PET. Similarly, micrometastases cannot be detected. Of six patients with incorrect N-staging on PET/CT, five were understaged.

Both PET/CT and CT were found to be highly accurate for M-staging, but this must be interpreted with caution on the basis of the limited follow-up of 447 days, the investigators said.

Also, they said, the image acquisition time must be considered another limitation of the combined PET/CT protocol. Compared with dedicated optimized CT protocols, the examination time was substantially longer, but less so for PET/CT without colonography. The examination time, the researchers added, may be improved by the development of alternative PET detector materials and the introduction of new detectors covering a larger field of view.

Finally, they said, four patients with a T1 tumor were identified in this study. Because CT and PET/CT have difficulty differentiating T1 from T2 tumors, which requires visibility of the wall layers in the colon, three of these tumors were staged incorrectly. Further technical development may resolve this failing, they said.

"In addition to optical colonoscopy, whole-body PET/CT colonography as an all-in-one staging modality seems feasible to provide an alternative to the multimodality, multistep staging in patients with colorectal cancer," Dr.Antoch said.

Summing up, the researchers said that this preliminary report suggests that PET/CT colonography may be at least equivalent to CT+PET with respect to tumor staging. The reasons for the 9% change in patient management, compared with conventional staging, may be attributed partially to the detection of synchronous tumors rather than to more accurate TNM staging.

Because all-in-one staging has to offer both accurate TNM staging and information on potentially present synchronous tumors, PET/CT along with optical colonoscopy may be suitable for whole-body all-in-one staging in patients with colorectal cancer, they investigators concluded.