Subsquamous Intestinal Metaplasia: Implications for Endoscopic Management of Barrett's Esophagus

CLINICAL GASTROENTEROLOGY AND HEPATOLOGY 2012;10:220 –224

REVIEWS Subsquamous Intestinal Metaplasia: Implications for Endoscopic Management of Barrett’s Esophagus PATRICK YACHIMSKI* and GARY W. FALK‡ *Division of Gastroenterology, Hepatology, and Nutrition, Vanderbilt University Medical Center, Nashville, Tennessee; and ‡Division of Gastroenterology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania

Buried Barrett’s, or subsquamous intestinal metaplasia (SSIM), is defined as the presence of metaplastic, columnar tissue beneath overlying squamous epithelium. Therefore, SSIM cannot be detected by endoscopic visual examination alone; it is detectable only by tissue biopsy. SSIM can develop in patients with Barrett’s esophagus (BE) after chronic pharmacologic suppression of gastric acid; it has been identified before and after endoscopic ablative therapies in cohort studies. It is important to determine the malignant potential of SSIM and the effects of endoscopic therapy for BE on development of SSIM; answers to these questions could affect long-term endoscopic surveillance and ablation strategies for patients with BE. Keywords: Neoplasm; Cancer; Esophageal Mucosa; Treatment; Risk; PPI.

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arrett’s esophagus (BE), defined as intestinal metaplasia of the esophageal mucosa, is the principal risk factor for esophageal adenocarcinoma.1 BE typically develops as a complication of chronic gastroesophageal reflux (Figure 1). Criteria for the diagnosis of BE have included mucosal changes in the tubular esophagus proximal to the anatomic gastroesophageal junction, which are detected by endoscopy, and the presence of columnar epithelium with goblet cells, detected by histopathology analysis. However, there is debate about the requirement for intestinal metaplasia in the diagnosis of BE. Non-goblet columnar metaplastic cells have abnormalities in DNA content also observed in intestinal metaplasia.2 Therefore, the risk of developing esophageal adenocarcinoma might be similar among patients with and without intestinal metaplasia.3 This issue is unresolved. Subsquamous intestinal metaplasia (SSIM), the presence of metaplastic, glandular BE tissue beneath normal-appearing overlying squamous epithelium, has been called buried Barrett’s (Figures 1 and 2), because SSIM is not visible during endoscopy but is detected only by examination of mucosal biopsy specimens. Although SSIM has been observed in patients with BE who have not received endoscopic ablative therapy and can coexist with BE that can be detected by endoscopy in these patients, SSIM has become the focus of increasing debate with the growing use of endoscopic therapy for BE. The presence of SSIM and magnitude of associated cancer risk influence the importance of endoscopic surveillance of patients with BE, including after endoscopic therapy. New im-

aging technologies that can detect SSIM might have a role in algorithms for endoscopic surveillance.

Pathophysiology and Prevalence Squamous re-epithelialization within segments of BE has been well-described in patients treated with proton pump inhibitors (PPIs). Reduced levels of acid in the distal esophagus after PPI therapy create an environment that promotes squamous regrowth. This re-epithelialization can be endoscopically apparent as isolated islands of squamous mucosa within a Barrett’s segment. In a study published in 1994, Sampliner4 reported development of squamous islands in 20 of 26 patients (77%) with long-segment BE that was treated with lansoprazole for an average of 2.9 years. A larger study of longer duration reported that the rate of squamous regrowth can increase over time; among 188 patients with BE who were treated with PPIs, 25% had endoscopic evidence of squamous islands 3 years later, whereas 100% had developed squamous islands after 12–13 years.5 The presence of SSIM beneath these squamous islands was demonstrated in a study by Sharma et al,6 in which squamous islands were targeted for endoscopic biopsy. SSIM was detected in 38.5% of biopsy samples from 22 patients with BE containing visible squamous islands after acid suppression therapy (18 received PPIs and 3 received histamine receptor antagonists) and in 45% of patients overall. The extent to which either squamous islands or SSIM exist in patients with BE who did not receive pharmacologic acid suppression is not known; no studies have reported detailed endoscopic and histopathologic findings at the time of diagnosis with BE from a cohort that had never received acid suppression therapy. Estimating the prevalence of SSIM among patients with established BE is not straightforward. In the Ablation of Intestinal Metaplasia Containing Dysplasia (AIM-Dysplasia) trial, a randomized controlled trial of radiofrequency ablation (RFA) versus a sham procedure for patients with BE and low- or high-grade dysplasia, 25% of subjects were found to have SSIM when the Abbreviations used in this paper: AIM-Dysplasia, Ablation of Intestinal Metaplasia Containing Dysplasia; APC, argon plasma coagulation; BE, Barrett’s esophagus; EMR, endoscopic mucosal resection; OCT, optical coherence tomography; PDT, photodynamic therapy; PHOPDT, Photofrin Plus Photodynamic Therapy; PPI, proton pump inhibitor; RFA, radiofrequency ablation; SSIM, subsquamous intestinal metaplasia. © 2012 by the AGA Institute 1542-3565/$36.00 doi:10.1016/j.cgh.2011.10.009

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Figure 1. BE is defined as intestinal metaplasia of the distal esophagus, in which normal squamous epithelium (A) is replaced by columnar epithelium (B), typically following chronic gastric acid and/or duodenal bile acid reflux. SSIM can be detected in some patients with BE following long-term treatment with PPIs and either before or after endoscopic ablation therapy. SSIM may exist in the absence of endoscopically visible columnar epithelium characteristic of BE (C) or may coexist with endoscopically visible BE (D). In some instances, careful histopathologic analysis may demonstrate that SSIM connects with the mucosal surface and visible BE (E). Relatively protected from luminal acid exposure, SSIM possesses unique biologic properties compared with surface epithelium (lower panel).

patients were enrolled before endoscopic therapy.7 Alternatively, in the Photofrin Plus Photodynamic Therapy (PHOPDT) study, a randomized controlled trial of porfimer sodium photodynamic therapy (PDT) versus PPIs in patients with BE and high-grade dysplasia, only 4.8% of subjects (10 of 208) were found to have SSIM when they were enrolled in the study.8 Both studies included subjects who underwent rigorous endoscopic surveillance and bi-

opsy analysis at high-volume centers with expertise in endoscopic and pathologic evaluation of BE. Other authorities contend that SSIM is rare, and that buried glandular tissue, when observed in biopsies, might be an artifact of the angle and technique of sample collection or tissue sectioning for histopathology analysis, or small areas of BE associated with squamous islands that were subtle or overlooked during visual

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Figure 2. Histopathology analysis demonstrates glandular epithelium beneath squamous epithelium, consistent with SSIM or buried Barrett’s; (A) 4⫻ magnification; (B) 10⫻ magnification. Images courtesy of Chanjuan Shi.

endoscopic analysis. The latter proposal is supported by a rigorous histopathology analysis performed by Hornick et al,9 which found that SSIM reaches the mucosal surface in most cases by wrapping around or penetrating squamous islands (Figure 1). The ability to detect SSIM in patients with BE could ultimately depend on the biopsy collection protocol, technique, and depth. Biopsy samples that do not contain lamina propria are not of sufficient depth to assess the presence of buried glandular tissue.10 Mucosal sampling with endoscopic mucosal resection (EMR) collects tissue from a larger surface area and of greater depth. However, limited data indicate that EMR does not detect SSIM more frequently than standard biopsy analysis. Compared with 25% of patients found to have SSIM on the basis of standard biopsy analysis in the AIM-Dysplasia trial,7 a single-center study found that 28% of patients with BE with high-grade dysplasia or intramucosal carcinoma who underwent EMR were found to have SSIM.11 EMR detected SSIM proximal to the squamous resection margin in a significant portion of patients, indicating the potential for the coexistence of SSIM and endoscopically visible BE.11

Malignant Potential of SSIM Dysplasia and adenocarcinoma have been reported in patients with SSIM identified after endoscopic therapies for BE, including PDT12,13 and argon plasma coagulation (APC).14 These reports raise concerns that patients with BE are at risk for cancer that arises from areas of SSIM that are not amenable to standard endoscopic surveillance, which consists of high-quality, white-light endoscopy in conjunction with 4-quadrant biopsies at 1- to 2-cm intervals. Several factors, however, should prompt careful consideration of this assumption. The first is that accurate histopathologic identification of dysplasia in SSIM can be challenging. Typical diagnostic criteria for dysplasia include detection of surface crypts. In the absence of surface crypts in areas of SSIM, regenerative atypia can be confused with dysplasia.15 Moreover, Hornick et al9 reported that in most cases, SSIM appeared to reach the esophageal mucosa; patients with SSIM that contained dysplasia were also found to have dysplasia in other locations within the BE segment.9 In the PHOPDT study of patients with SSIM after PDT, the highest grades of dysplasia (or cancer) detected in the endoscopic follow-up examinations were also detected in biopsy samples from the surface epithelium; they were not concealed or contained exclusively in SSIM.8 SSIM has biological properties that are distinct from surface BE,15 perhaps as a consequence of reduced exposure to luminal

contents, which include gastric acid and bile acid refluxate.16 SSIM has reduced rates of crypt proliferation, on the basis of analysis of Ki-67, compared with BE tissue from patients before therapy,15,16 and no aneuploidy after PDT.16 SSIM might therefore have less malignant potential than surface BE. However, areas of SSIM have higher levels of Ki-67, cyclooxygenase-2, and BCL-2 than normal squamous epithelium (Figure 1).17 The total number of reported cases of adenocarcinoma that originated from SSIM is limited. Samples collected by EMR in a cohort of patients without a history of prior endoscopic therapy revealed 1 case of intramucosal adenocarcinoma that arose from SSIM but no cases of invasive adenocarcinoma.11 A recent pooled analysis of results of 9 published studies tallied 34 cases of neoplasia in areas of SSIM after endoscopic therapies that included PDT, APC, and laser ablation: 1 case of low-grade dysplasia, 13 cases of high-grade dysplasia, 11 cases of intramucosal carcinoma, and 6 cases of invasive adenocarcinoma.18 There are no specific data on cancer mortality associated with SSIM; progression of SSIM into cancer might be a rare event.

Effects of Endoscopic Therapy on Subsquamous Intestinal Metaplasia SSIM has been detected after endoscopic therapy for BE that uses any ablation technique, including PDT,8,12,13 RFA,7 APC,19 multipolar electrocoagulation,20 and cryoablation.21 The mechanisms, extent, and depth of mucosal injury vary among these techniques, along with, in some cases, the tissue response to injury. The exact effects of endoscopic ablation therapy on SSIM might therefore depend on the technique used. It is important to consider whether endoscopic ablation therapy affects the prevalence and progression of SSIM. Data from the PHOPDT study showed that of 138 subjects treated with PDT (and PPI therapy), 5.8% had SSIM when the study began, and 30% had SSIM at the 5-year follow-up examination. However, the controls, who received only PPI therapy, had a comparable prevalence of SSIM at the 5-year follow-up examination (33%).8 Therefore, endoscopic ablation therapy for BE does not appear to accelerate development of SSIM, at least compared with PPI therapy. Alternatively, the AIM-Dysplasia trial reported that RFA might decrease the prevalence of SSIM. When the study began, 25.2% of the subjects, who had never received ablation therapy, had evidence of SSIM. Among subjects who then received RFA and PPI therapy, the prevalence of SSIM decreased to 5.1% after 12 months7 and 3.8% after 24 months.22

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However, the prevalence of SSIM was 40% at the 12-month follow-up examination of subjects who received a sham procedure and PPI therapy.7 The reported prevalence of SSIM varies among studies and cohorts, even for a specific ablation technology such as RFA. The estimated post-ablation prevalence of SSIM of 5.1% (at 12 months) and 3.8% (at 24 months) among patients who received RFA in the AIM-Dysplasia trial22 are higher than the prevalence reported in other RFA cohorts. In a prospective, multicenter study of patients with nondysplastic BE who were treated with RFA (the Aim-II trial), analysis of 1473 biopsy specimens, obtained from 50 subjects 5 years after RFA, revealed no evidence of SSIM. Eighty-five percent of the biopsy samples contained lamina propria or deeper structures, of adequate depth to assess the presence of SSIM.23 A high-volume endoscopic center that specializes in BE therapy, in Amsterdam, also reported that they did not detect SSIM in any biopsy24 or EMR samples25 from patients who received RFA or a combination of RFA and EMR. Extended follow-up analyses of these cohorts are required to determine whether the prevalence of SSIM remains low for longer time periods after ablative therapy. Estimates of SSIM after endoscopic therapy might vary among studies because of differences in defining lamina propria in neosquamous epithelium. Two studies that examined biopsy depth after ablative therapy (one cohort of patients was treated with RFA26 and another received RFA and PDT27) reported no differences in the proportion of biopsies that contained lamina propria before and after the ablative procedure. In the former study, however, biopsies that contained lamina propria papillae were classified as lamina propria27; evaluation of only lamina propria papillae might not be sufficient to detect SSIM.18

Imaging Technologies Optical coherence tomography (OCT) allows high-resolution, cross-sectional imaging of tissue. Prototype OCT and optical frequency domain imaging devices (some use a rotating imaging probe and an esophageal centering balloon, with standardized pullback through the gastroesophageal junction) have been developed and studied for their ability to identify and characterize BE.28,29 Images captured by these techniques can be used to identify dysplasia, on the basis of cellular architecture,29 and image to sufficient depth to visualize subsurface and submucosal structures.28 OCT identified SSIM at a depth of 300 – 500 ␮m, beneath neosquamous epithelium and lamina propria, in a patient who had undergone RFA.30 The ability to detect SSIM and strategies for endoscopic surveillance of BE could be altered by imaging techniques such as OCT, if they provide consistent identification of subsurface structures. However, the use of OCT to identify SSIM will require development of a reliable, easy to use, intuitive imaging platform, demonstration that findings are reproducible (in intraobserver and interobserver interpretation), and a cost-effective implementation strategy for widespread use.

Future Directions Diagnosis and accurate staging of BE are not always straightforward because of the potential for endoscopic biopsy sampling errors and variations in histopathologic grading of dysplastic tissues. Conflicting standards for the histopathologic diagnosis of BE (such as whether the presence of goblet cells is required for diagnosis) and evolving algorithms for endoscopic

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management options add complexity to the management of BE. The concept of buried Barrett’s (SSIM) challenges the belief that endoscopically visible columnar epithelium is requisite for the diagnosis of BE and adds new terminology to the discussion. Criteria for determining which patients are eligible for endoscopic ablation therapy for BE are changing. The American Gastroenterological Association medical position statement recommends endoscopic therapy as a treatment option for BE that contains high-grade dysplasia and proposes that RFA could be considered for patients with BE that contains low-grade dysplasia as well as select patients with nondysplastic BE who are at high risk for progression to cancer. However, the specific criteria for identifying this high-risk population have not been defined.31 There are few data from controlled prospective trials that support measurable effects of endoscopic therapy on development of esophageal cancer or cancer mortality, particularly for patients with nondysplastic BE. A cost-utility analysis (a simulation model over a range of specified assumptions) of RFA for patients with BE and low-grade dysplasia or without dysplasia showed that RFA might be an acceptable strategy and accounted for the possibility of SSIM.32 Alternatively, decreasing trends in estimates of cancer incidence among patients with BE (0.3% per year for nondysplastic BE in one recent study33) challenge assumptions about the cost-effectiveness of endoscopic therapy and endoscopic surveillance for BE. Defining the clinical implications of SSIM will require prospective, longitudinal, follow-up analyses of large cohorts of patients who receive endoscopic surveillance, endoscopic therapy, or both, along with cooperation among different areas of research. Endoscopic screening studies that identify new incident cases of BE should attempt to assess and report the prevalence of SSIM in these patients. Prospective studies of endoscopic surveillance or endoscopic therapy for BE should also determine the prevalence of SSIM longitudinally at various time points as BE progresses, with or without therapy. In these studies, the biopsy protocol, techniques, and depth and adequacy of tissue assessment should be carefully described, with adherence to a consistent and standardized definition of lamina propria during biopsy analysis of neosquamous epithelium. Gastroenterologists should develop and maintain proficiency in techniques of esophageal biopsy. We advocate the “turn-and-suck” method, in which the tip of the endoscope is gently deflected and endoscopic suction applied during biopsy. Collection of biopsy samples by using jumbo forceps has not been shown to be more effective than using standard forceps in detection of SSIM. Esophageal biopsy samples, particularly those from patients with dysplasia, should be carefully reviewed by gastrointestinal pathologists who devote specific attention to identifying SSIM. Given the limitations of esophageal biopsy sample analysis, EMR specimens and, when available, esophagectomy specimens from patients who have undergone esophagectomy for BE that contains dysplasia or neoplasia should be carefully evaluated for the presence and extent of SSIM. The phenotypic characteristics of SSIM should be compared with those of surface BE, especially as novel tissue biomarkers are identified. By using these techniques, gastroenterologists and BE researchers could increase understanding of the clinical importance of SSIM, which is widely discussed but a topic of much uncertainty. It is still unclear whether SSIM is a significant risk

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factor for progression to malignancy or follows an indolent course in most patients. On the basis of current data, concern about SSIM should not fundamentally alter current approaches for selecting endoscopic surveillance and/or treatment options for patients with BE. References 1. Falk GW. Barrett’s esophagus. Gastroenterology 2002;122: 1569 –1591. 2. Liu W, Hahn H, Odze RD, et al. Metaplastic esophageal columnar epithelium without goblet cells shows DNA content abnormalities similar to goblet cell-containing epithelium. Am J Gastroenterol 2009;104:816 – 824. 3. Kelty CJ, Gough MD, Van Wyk Q, et al. Barrett’s oesophagus: intestinal metaplasia is not essential for cancer risk. Scand J Gastroenterol 2007;42:1271–1274. 4. Sampliner RE. Effect of up to 3 years of high-dose lansoprazole on Barrett’s esophagus. Am J Gastroenterol 1994;89:1844 –1848. 5. Cooper BT, Chapman W, Neumann CS, et al. Continuous treatment of Barrett’s oesophagus patients with proton pump inhibitors up to 13 years: observations on regression and cancer incidence. Aliment Pharmacol Ther 2006;23:726 –733. 6. Sharma P, Morales TG, Bhattacharyya A, et al. Squamous islands in Barrett’s esophagus: what lies underneath? Am J Gastroenterol 1998;93:332–335. 7. Shaheen NJ, Sharma P, Overholt BF, et al. Radiofrequency ablation in Barrett’s esophagus with dysplasia. N Engl J Med 2009; 360:2277–2288. 8. Bronner MP, Overholt BF, Taylor SL, et al. Squamous overgrowth is not a safety concern for photodynamic therapy for Barrett’s esophagus with high-grade dysplasia. Gastroenterology 2009; 136:56 – 64. 9. Hornick JL, Blount PL, Sanchez CA, et al. Biologic properties of columnar epithelium underneath reepithelialized squamous mucosa in Barrett’s esophagus. Am J Surg Pathol 2005;29:372–380. 10. Biddlestone LR, Barham CP, Wilkinson SP, et al. The histopathology of treated Barrett’s esophagus: squamous reepithelialization after acid suppression and laser and photodynamic therapy. Am J Surg Pathol 1998;22:239 –245. 11. Chennat J, Ross AS, Konda VJ, et al. Advanced pathology under squamous epithelium on initial EMR specimens in patients with Barrett’s esophagus and high-grade dysplasia or intramucosal carcinoma: implications for surveillance and endotherapy management. Gastrointest Endosc 2009;70:417– 421. 12. Mino-Kenudson M, Ban S, Ohana M, et al. Buried dysplasia and early adenocarcinoma arising in Barrett esophagus after porfimerphotodynamic therapy. Am J Surg Pathol 2007;31:403– 409. 13. Overholt BF, Panjehpour M, Halberg DL. Photodynamic therapy for Barrett’s esophagus with dysplasia and/or early stage carcinoma: long-term results. Gastrointest Endosc 2003;58:183–188. 14. Van Laethem JL, Peny MO, Salmon I, et al. Intramucosal adenocarcinoma arising under squamous re-epithelialisation of Barrett’s oesophagus. Gut 2000;46:574 –577. 15. Odze RD, Lauwers GY. Histopathology of Barrett’s esophagus after ablation and endoscopic mucosal resection therapy. Endoscopy 2008;40:1008 –1015. 16. Hornick JL, Mino-Kenudson M, Lauwers GY, et al. Buried Barrett’s epithelium following photodynamic therapy shows reduced crypt proliferation and absence of DNA content abnormalities. Am J Gastroenterol 2008;103:38 – 47. 17. Lewis CJ, Thrumurthy SG, Pritchard S, et al. Comparison of COX-2, Ki-67, and BCL-2 expression in normal esophageal mucosa, Barrett’s esophagus, dysplasia, and adenocarcinoma with postablation mucosa and implications for ablative therapies. Surg Endosc 2011;25:2564 –2569.

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Reprint requests Address requests for reprints to: Patrick Yachimski, MD, MPH, 1660 The Vanderbilt Clinic, Nashville, Tennessee 37232-5280. e-mail: [email protected]; fax: (615) 343-8174. Conflicts of interest This author discloses the following: Patrick Yachimski has received research support from BARRX Medical. The remaining author discloses no conflicts.