PET/CT-Colonography: One-Stop Colorectal Cancer Staging
Abstract & Commentary
By William B. Ershler, MD, INOVA Fairfax Hospital Cancer Center, Fairfax, VA; Director, Institute for Advanced Studies in Aging, Washington, DC.
Synopsis: In 47 patients with newly diagnosed colorectal cancer, staging by combined CT and PET was compared to CT followed at a later time by PET or by CT alone. With regard to TNM staging, the combined CT/PET colonography proved more accurate than CT alone and was comparable in accuracy to CT and PET obtained on separate occasions. Thus, a single imaging protocol may become the standard staging approach once these findings are confirmed by more extensive trial.
Source: Veit-Haibach P, et al. Diagnostic accuracy of colorectal cancer staging with whole-body PET/CT colonography. JAMA. 2006;296:2590-2600.
Clinical staging of colorectal cancer is performed to guide therapy. Typically, after colonoscopy, computerized tomography (CT) of the chest, abdomen and pelvis is obtained, and from this a primary approach is formulated. Recently, there has been increased utilization of positron emission tomography (PET) in the initial staging as well. Whereas CT scans provide anatomic detail, PET displays functional information based upon metabolic activity and this has proven accurate for local and metastatic colorectal cancer.1-4 The complimentary information provided by CT and PET has led to the commercial development of combined PET/CT scanners which offer the convenience of a one step staging procedure.
Veit-Haibach and colleagues throughout Germany have performed a prospective study of 47 patients with newly-diagnosed primary colorectal cancer to determine the staging accuracy of whole-body PET/CT colonography compared with the staging accuracies of CT followed by PET (CT+PET) and CT alone. On the day following colonoscopy, patients were examined by PET/CT colonography. The PET/CT colonography protocol included bowel relaxation/distension using scopolamine intravenous infusion and rectal water enema (2-3L at 37°C). Patients were followed for a mean of 447 days (range, 232-653 days).
The combined CT/PET colonography protocol correctly identified TNM stage in 74% of cases, whereas the sequential CT+PET was correct in 64% and CT alone (without PET) was correct in 52%. This 22% difference in accuracy between CT/PET compared to optimized CT alone proved statistically significant (P = .003). Examining the TNM characteristics of each patient, the gain in accuracy was primarily due to a greater precision in the T stage afforded by PET/CT compared to optimized CT alone. In contrast, there were no significant differences in assessing nodal (N) or distant metastatic (M) status among the three arms. With regard to nodal status, when a threshold for calling a node positive was 0.7 cm, CT alone was accurate 76% of the time (compared with PET/CT 86%), but when a 1 cm threshold was employed, the CT accuracy fell to 62% (ie, nodal status was under-staged in an additional 6 patients).
Of the 47 patients, therapy decisions were altered in 4 patients based upon the findings provided by the PET/CT protocol. For example, in one patient thought to have a single hepatic metastasis on the basis of conventional CT, a second small hepatic lesion was identified. Although this did not change the TNM stage, detection of the second lesion altered management to include a more extended surgical approach.
Commentary
Thus, one may conclude from this report that a single stage PET/CT colonography protocol is a staging strategy worthy of consideration. It proved to be more accurate than an optimized CT protocol (without PET), particularly in assessing primary tumor (T) status, and was at least as accurate as CT followed separately by PET. Although a more accurate assessment of T status would seem of marginal importance in the primary management of colon cancer, for rectal cancer its potential value is more apparent. For example, a more precise determination of T status may help to select those who would benefit from neoadjuvant therapy compared with resection alone. Furthermore, accurate assessment of tumor size may aid in determining the optimal surgical approach (eg, laparotomy, laparoscopy, or transanally).
Compared to sequential CT followed on a later occasion by PET, the accuracy was at least equivalent and the added value of the combined protocol would relate to the convenience of a single procedure and more timely results. Questions that warrant further clarification relate to the overall technical feasibility and costs incurred by performing PET on all preoperative colorectal patients. If the data support utilization of PET in the staging of colorectal cancer patients, then it would make sense that a single PET/CT colonography approach should be implemented.
References
1. Rohren EM, et al. Clinical applications of PET in oncology. Radiology. 2004;231:305-332.
2. Kalff V, et al. The clinical impact of (18)F-FDG PET in patients with suspected or confirmed recurrence of colorectal cancer: a prospective study. J Nucl Med. 2002;43:492-499.
3. Huebner RH, et al. A meta-analysis of the literature for whole-body FDG PET detection of recurrent colorectal cancer. J Nucl Med. 2000;41:1177-1189.
4. Antoch G, et al. Accuracy of whole-body dual-modality fluorine-18-2-fluoro-2-deoxy-D-glucose positron emission tomography and computed tomography (FDG-PET/CT) for tumor staging in solid tumors: comparison with CT and PET. J Clin Oncol. 2004;22:4357-4368.
In 47 patients with newly diagnosed colorectal cancer, staging by combined CT and PET was compared to CT followed at a later time by PET or by CT alone.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content