| Japanese Journal of Clinical Oncology | Pages |
Primary Colorectal Cancers Detected with PET
Introduction
Case Report
Case 1
Case 2
Case 3
Discussion
References
Primary Colorectal Cancers Detected with PET
INTRODUCTION
Whole-body positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) has been used successfully in oncological indications. We are using whole-body FDG PET for cancer screening (1). By PET screening, 15 asymptomatic participants were found to have malignant tumors. Among them, three were found to have colorectal cancer; subsequently they underwent potentially curative surgery. These three cases are presented and the potential utility of PET in the diagnosis of primary colorectal cancer is discussed.
CASE REPORT
PET screening is performed with a whole-body PET scanner (ECAT EXACT47, Siemens/CTI, Knoxville, TN). Participants are fasted for at least 6 h before examinations. About 45-60 min after intravenous administration of 260-370 MBq of FDG, emission scanning is performed from the pelvis to the maxilla. Transmission scanning for attenuation correction is not performed. All gray-scale hard copy images of transaxial slices are printed out and evaluated visually; images of coronal and sagittal slices are also available. Between September 1994 and March 1997, 1872 participants (1214 men and 658 women, mean age 52.4 ± 10.1 years) underwent PET screening and three asymptomatic persons were found with colorectal cancers. They underwent subsequent surgery. Histopathologically, the tumors were adenocarcinomas and lymph node metastasis was not observed. No evidence of recurrence has been observed for 36, 27 and 14 months, respectively. The patients' characteristics are summarized in Table 1 and pertinent details of the cases are as follows.
Case 1
A 45-year-old man. On PET images, high FDG uptake was easily noticed in the ascending colon (Fig. 1). Colonoscopy revealed a colon cancer and right hemicolectomy was performed.
Case 2
A 53-year-old man. On PET images, increased FDG uptake was observed above the urinary bladder (Fig. 2). Subsequent colonoscopy revealed a rectal cancer (rectosigmoid region) and anterior resection was performed.
Case 3
A 40-year-old woman. On PET images, high FDG uptake was discovered in the ascending colon (Fig. 3). Colonoscopy revealed a colon cancer and right hemicolectomy was perfomed.
DISCUSSION
By PET screening, three asymptomatic participants were found to have primary colorectal cancer. The detection rate for colorectal cancer (not including carcinoma in situ) was 0.16% (three out of 1872 participants), corresponding to a rate of 1.44-1.72 per 1000 person-years recently reported in association with a colorectal cancer screening program (2,3). The tumors of the three patients were classified as Stage I or II (TNM classification). The 5-year survival rate associated with these stages is favorable: 85% for Stage I and 70% for Stage II (4). Hence the surgeries were deemed successful.
Table 1.
| Case No. | Age (yr) | Sex | Cancer location | Tumor size (cm) | FOB | CEA (ng/dl) | TNM classification* | Stage* |
| 1 | 45 | M | Ascending | 3.5 | + | NE | pT3,pN0,M0 | II |
| 2 | 53 | M | Rectosigmoid | 4 | + | 0.1 | pT3,pN0,M0 | II |
| 3 | 40 | F | Ascending | 6 | NE | 0.1 | pT2,pN0,M0 | I |
Figure 1. Case 1. On a coronal tomographic PET image, high FDG accumulation is obvious in the ascending colon (arrow). Physiological urinary FDG excretion is also seen in the bladder. Figure 2. Case 2. On a coronal tomographic image, focal FDG accumulation is noted above the urinary bladder (arrow). Figure 3. Case 3. On six consecutive coronal tomographic images, increased FDG uptake is clearly visible in the ascending colon (arrow). Each slice is shown from the front to the back at 3 mm intervals. FDG uptake in the brain and myocardium is normal.
Our institution is a membership-based medical health club and most screened members are followed up. So far, false-negative results have not been observed, but the 16-34-month follow-up periods are too short to confirm this. At least seven participants underwent colonic examination after screening because of positive PET results. One was found with colonoscopy to have ulcerative colitis at the descending colon and the other was diagnosed with severe proctitis. Because high FDG uptake can be observed in inflammation of the bowel (5), localized inflammatory lesions can result in false-positive findings. Physiological bowel FDG uptake also varies considerably in healthy persons. Five of the seven proved to be normal; the high FDG uptake was due to physiological bowel uptake. To date, the clinical utility of PET remains undetermined in patients with primary colorectal cancer. In two reports, however, high FDG uptake was recognized in all primary colorectal cancers (6,7). Our experience and the PET results described in these reports support PET as both a screening method and a diagnostic procedure. In colorectal cancer screening of the general population, the fecal occult blood (FOB) test is used effectively. In comparison, PET is inappropriate for screening large populations because it is costly and takes a great deal of time ([sim]35 min scanning time). Among the screening methods available, colonoscopy is the most sensitive. PET is not as sensitive as colonoscopy. The advantages of PET are that it does not require bowel preparation and that it surveys the entire body, the colon and rectum included, non-invasively in a single examination. The validity of using PET as a screening method should be evaluated in further studies. As diagnostic procedures for primary colorectal cancer, both colonoscopy and double-contrast barium study are the gold standards. Therefore, the application of PET is limited. PET can be used in the distinction between benign and malignant non-epithelial tumors when differential diagnosis is difficult with colonoscopy or barium study. In our personal experience (unpublished), PET gave true positive results for several primary colorectal cancers and a true negative result for a mucinous cystadenoma of the appendix. Other indications might be in patients with large bowel stenosis and in high-risk patients, owing to its non-invasiveness, comprehensiveness and absence of bowel preparation. In the preoperative assessment of primary colorectal cancer, it is important to evaluate regional lymph node metastasis and distant metastasis (8). Colonoscopy and barium study cannot be used reliably to evaluate extracolonic tumor extension. For such evaluation, various imaging methods are available: ultrasonography, endosonography, CT, MRI, immunoscintigraphy and PET. The same advantages of PET apply: both primary and metastatic lesions can be detected non-invasively in a single study. In this respect, PET seems to be superior to ultrasonography, CT or MRI. PET also seems to be superior to immunoscintigraphy in image quality: tumors are depicted more intensely with PET than with immunoscintigraphy. To determine more fully the potential utility of PET in the diagnosis of primary colorectal cancer, studies comparing PET and conventional imagings are needed. Because the number of PET facilities is increasing, opportunities to use PET are also increasing. It is important to recognize that primary colorectal cancer can be intensely depicted with PET in the resectable stage. Further studies will establish its role in the diagnosis and management of primary colorectal cancer.
References
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