Administration of 200 mg of celecoxib or placebo twice daily for 48 weeks of treatment did not change the proportion of biopsy samples diagnosed with dysplasia or cancer among patients with Barrett’s dysplasia. During the first year of treatment 36 (44%) of the 82 patients experienced no change in their highest grade of dysplasia. Approximately 50% of patients in the low-grade stratum and 25% of patients in the high-grade stratum, regardless of treatment assignment, experienced a decrease in the highest grade of dysplasia. This decreased percentage of patients in the highest grade of dysplasia without additional treatment underscores the difficulties in tissue biopsy sampling, our lack of understanding of the natural history of Barrett’s esophagus, and the variability of histologic diagnosis (30
This study has several limitations. The difficulty in tissue biopsy sampling can be demonstrated by the 122 CBET patients who were registered but were not randomly assigned to treatment. Most of these registered patients had a preregistration histologic diagnosis of dysplasia, but they did not have evidence of dysplasia at the time of their baseline endoscopy. Despite the intensive endoscopic biopsy protocol, the area that was used to establish the initial preregistration diagnosis of dysplasia may not have been sampled. Among the 122 registered but not included patients, 83 patients were diagnosed as indefinite for dysplasia. The intensive endoscopic biopsy protocol resulted in a new diagnosis of esophageal cancer for 15 registered patients. Tissue biopsy sampling, al though imperfect, is currently the best available method to assess the malignant potential of Barrett’s esophagus.
Another limitation is that natural reversion of dysplasia without any intervention was more likely to occur in patients with low-grade dysplasia than with high-grade dysplasia. More patients in the high-grade stratum in the placebo arm (25%) experienced an increase in their highest grade of dysplasia than patients in the low-grade stratum (11%). This observation further illustrates the clinical challenge posed for physicians in the management of patients with high-grade dysplasia.
A final limitation is that dysplasia grading is an imperfect predictor of cancer because of the low intra- and interobserver agreement among pathologists (31
). The low degree of inter-observer agreement in diagnosing low-grade dysplasia may contribute to histologic inconsistency of dysplasia. This inconsistency may create the false appearance of histologic reversion. Although the interobserver agreement in diagnosing high-grade dysplasia was much higher in our previous study (32
),it was not 100%. The CBET investigators sought to minimize this limitation by requiring a majority histologic diagnosis of dysplasia for entry into this study. This requirement increased the complexity of randomization process and had an impact on patient accrual, but it provided more confidence in the histologic diagnosis.
Whether celecoxib treatment would alter the portion of the esophagus (i.e., the length of esophagus) affected by Barrett’s esophagus was unknown. Because of the difficulty in using centimeter markings on the upper endoscope to appropriately determine length of Barrett’s esophagus, we measured the total surface area affected by Barrett’s esophagus by use of a quantitative endoscopic examination. The median total surface area affected by Barrett’s esophagus at baseline in patients with low- and high-grade dysplasia was similar. This result was expected because having a higher grade of dysplasia does not necessarily mean a larger total surface area of Barrett’s esophagus. Treatment with celecoxib for 48 weeks, compared with placebo, did not change the total sur face area affected by Barrett’s esophagus, regardless of grade.
Similarly, treatment with celecoxib for 24 weeks compared with placebo did not change the levels of COX-2 mRNA, PGD2, PGE2, PGF2α, thromboxane B2, or 6-keto-PGF1α, regardless of grade. This finding was unexpected. The samples obtained for biomarker studies were adjacent to tissue biopsies with histologic confirmation of dysplasia. However, the samples for biomarker studies themselves had no histologic confirmation of dysplasia. We recognize that Barrett’s esophagus is multifocal and patchy in nature. So, it is possible, although unlikely, that the samples used for these biomarker assays were not dysplastic tissue. Additional studies that evaluate COX-2 expression by immunohistochemistry in dysplastic tissues appear to be warranted.
Although we found no changes in the levels of COX-2 mRNA, we did anticipate differences in the levels of prostaglandin between the two treatment arms based on the proposed mechanism of action of COX-2 inhibitors. The lack of differences in prostaglandin levels regardless of treatment arm or dysplasia grade indicated that the celecoxib dose was probably inadequate. At the initiation of CBET, the 200-mg dose of celecoxib twice daily was selected because of concerns for safety and for tolerability in a trial of potentially long duration (up to 3 years). However, a 400-mg dose of celecoxib twice daily may be more biologically meaningful (33
). As expected, tumor suppressor genes p16, APC, and E- cadherin were methylated in samples with low- or high-grade dysplasia. After the 48-week treatment with celecoxib or placebo, no statistically significant change in methylation levels from baseline in either group was found, which is not surprising given the lack of histologic changes. Methylation of these three genes, or of any other hypermethylated locus, should not be directly affected by COX-2 inhibition; therefore, we cannot rule out the possibility that these genes are potential markers of molecular changes underlying the histologic changes associated with dysplasia. We have previously observed that histologic progression is associated with underlying progression in the number of hypermethylated loci in squamous cell carcinoma of the esophagus (24
). The higher rate of methylation of the genes for p16, APC, and E-cadherin in samples with high-grade dysplasia compared with samples with low-grade dysplasia, which we found in this study, support the possibility that hypermethylation of multiple loci may compliment histologic changes as a surrogate for disease progression and should be investigated in future studies.
The lack of a statistically significant difference between the treatment groups that we observed was not due primarily to inadequate recruitment. The study was powered at 80% for a total of 124 patients overall. Only 100 patients were randomly assigned to treatment, and only 82 (43 in the celecoxib arm and 39 in the placebo arm) of the 100 patients contributed data to the comparison for the primary outcome. But because the effect size was–2% (i.e., an 8% decrease in the combined celecoxib group and a 6% decrease in the combined placebo group in the proportion of biopsy samples with dysplasia or cancer at 48 weeks), the addition of 42 patients would most likely not result in a statistically significant difference between celecoxib and placebo groups. The result is essentially null, i.e., an effect size of 0. More subjects will not make such a result statistically significant.
The apparent inability of celecoxib, compared with placebo, to decrease the percentage of samples with dysplasia is probably not due to the patient population. The characteristics of CBET patients, as anticipated, were typical of patients with Barrett’s dysplasia: white males who were aged 60–70 years, who were overweight or obese, and who were taking antireflux medications (e.g., proton pump inhibitors or histamine H2
-receptor antagonists). It is not unusual for patients with Barrett’s esophagus to be on such medications because it was probably their symptoms of gastroesophageal reflux disease that led them to undergo clinical evaluation for Barrett’s esophagus. Whether the antireflux medications could be associated, either positively or negatively, with dysplasia modification is unknown. Despite several studies, the association of antireflux medications with the reversion of low- or high-grade dysplasia in Barrett’s esophagus remains unclear (34
Although celecoxib treatment was associated with increased cardiovascular toxic effects in another trial (37
), we found that patients in the placebo arm experienced more cardiovascular toxic effects than those in the celecoxib arm, although the total number of patients with such toxic effects was small. Another potential toxic effect was gastrointestinal adverse events, but such events were low and similar in both treatment arms. Thus, daily treatment with celecoxib (400 mg) for up to 2 years, compared with placebo, was reasonably well tolerated with few serious adverse events.
Sixty-four (64%) of 100 patients randomly assigned to treatment into CBET had low-grade dysplasia. Before study entry, patients with high-grade dysplasia were offered the standard-of-care surgery and additional treatments, including photodynamic therapy and mucosal ablation. These patients were aware of other treatment options, refused surgery, and understood the risks associated with a placebo-controlled trial. Although patients with high-grade dysplasia had a 50% chance of being randomly assigned to the placebo arm, all patients with high-grade dysplasia remained under close surveillance, undergoing rigorous endoscopic biopsies every 3 months. Six patients in the high-grade stratum were diagnosed with esophageal adenocarcinoma through their endoscopic biopsy specimens within their first year on study (three in the celecoxib arm and three in the placebo arm). Of the four patients who underwent esophagectomy, two patients were diagnosed with high-grade dysplasia with no evidence of invasive adenocarcinoma, and despite the initial diagnosis of esophageal cancer on the endoscopic biopsy specimen, there was no evidence of invasive cancer in the postresection specimen. The six patients diagnosed with esophageal cancer had Barrett’s esophagus for periods of several months to 20 years. The variability in the clinical course of this disease underscores the management challenges posed by highgrade dysplasia, including the requirement for an upper endoscopy examination every 3 months, the lack of predictive markers to determine risk of disease progression, and the difficulties with sampling variation.
The lack of secondary chemoprevention with celecoxib in patients with Barrett’s dysplasia was disappointing. However, CBET is one of the few prospective chemoprevention trials in patients with Barrett’s dysplasia, and through it, we have gained valuable information about the disease process and the challenges of conducting such a study.