DNA mismatch repair deficiency but not ARID1A loss is associated with prognosis in small intestinal adenocarcinoma

Medullary carcinomas of the nonampullary small intestine: association with coeliac disease, mismatch repair deficiency, PD-L1 expression, and favourable prognosis

AIM

Gastrointestinal medullary carcinoma is a rare histologic subtype of adenocarcinoma. As nonampullary small bowel medullary carcinomas (SB-MCs) are poorly characterized, we aimed to analyse their clinicopathologic and immunohistochemical features and to compare them with nonmedullary small bowel adenocarcinomas (NM-SBAs).

METHODS AND RESULTS

Surgically resected SBAs collected through the Small Bowel Cancer Italian Consortium were classified as SB-MCs (carcinomas with ≥50% of tumour fulfilling the typical histologic criteria of MC) or NM-SBAs. Immunohistochemistry for cytokeratin (CK)7, CK20, CDX2, programmed death-ligand 1 (PD-L1) and mismatch repair proteins was performed in both SB-MCs and NM-SBAs. SB-MCs were also tested for CK8/18, synaptophysin, SMARCB1, SMARCA2, SMARCA4, and ARID1A and for Epstein-Barr virus (EBV)-encoded RNAs by in-situ hybridization. MLH1 promoter methylation status was evaluated in MLH1-deficient cases. Eleven SB-MCs and 149 NM-SBAs were identified. One (9%) SB-MC was EBV-positive, while 10 (91%) harboured mismatch repair deficiency (dMMR). MLH1 promoter hypermethylation was found in all eight dMMR SB-MCs tested. Switch/sucrose nonfermentable deficiency was seen in two (18%) SB-MCs, both with isolated loss of ARID1A. Compared with NM-SBAs, SB-MCs exhibited an association with coeliac disease (P < 0.001), higher rates of dMMR (P < 0.001), and PD-L1 positivity by both tumour proportion score and combined positive score (P < 0.001 for both), and a lower rate of CK20 expression (P = 0.024). Survival analysis revealed a better prognosis of SB-MC patients compared to NM-SBA cases (P = 0.02).

CONCLUSION

SB-MCs represent a distinct histologic subtype, with peculiar features compared to NM-SBAs, including association with coeliac disease, dMMR, PD-L1 expression, and better prognosis.

Mismatch repair deficiency as prognostic factor for stage III small bowel adenocarcinoma: A multicentric international study

BACKGROUND

Small bowel adenocarcinoma (SBA) is a rare cancer with an aggressive behavior. No study has specifically addressed the putative prognostic role of mismatch repair status in stage III SBAs.

AIMS

We aimed to investigate whether mismatch repair deficiency is associated with cancer-specific survival in a Western cohort of patients with stage III SBAs.

METHODS

In this retrospective multicentric international cohort study, we enrolled 70 patients who underwent surgically resection for stage III SBAs and we analyzed the frequency of mismatch repair deficiency, tested by immunohistochemistry for mismatch repair proteins and by polymerase chain reaction for microsatellite instability, and its association with cancer-specific survival and other clinic-pathologic factors.

RESULTS

We found sixteen (23%) patients with mismatch repair deficient adenocarcinoma, without discordance between immunohistochemical and polymerase chain reaction for microsatellite instability analyses. Mismatch repair deficiency proved to be associated with a better outcome both at univariable analysis (hazard ratio: 0.28, 95% confidence interval: 0.08-0.91, p: 0.035) and in bivariable models adjusted for patient age or gender, tumor site, pT4 stage, tumor budding, and perineural invasion.

CONCLUSION

This study highlights the importance of testing mismatch repair status to improve prognostic stratification in stage III SBAs.

Microsatellite instability in the high-grade dysplasia component of duodenal adenoma is associated with progression to adenocarcinoma

PURPOSE

We examined the microsatellite instability of duodenal tumors to evaluate their molecular features associated with the adenoma-carcinoma sequence.

METHODS

Fifty-two non-ampullary duodenal epithelial tumors collected by endoscopic mucosal resection or surgical resection were studied. When a tumor had two or more dysplasia grades, the highest grade was considered. Representative areas were macro-dissected and subjected to a microsatellite instability analysis and immunohistochemical staining.

RESULTS

The 52 tumors were classified as either adenoma with low-grade dysplasia (n = 18), adenoma with high-grade dysplasia (n = 20), or adenocarcinomas (n = 14). Among these, 3 adenocarcinoma cases showed microsatellite instability and the remaining 49 tumors showed microsatellite stability. Of the 14 adenocarcinoma cases, 3 contained both high-grade dysplasia and adenocarcinoma components, and 11 contained only the adenocarcinoma component. Interestingly, all three adenocarcinoma + high-grade dysplasia cases were microsatellite instability-high in both the adenocarcinoma and high-grade dysplasia components. Immunohistochemical staining of mismatch repair proteins showed mismatch repair deficiency in three microsatellite instability-high adenocarcinoma + high-grade dysplasia cases.

CONCLUSIONS

Only adenocarcinoma cases with high-grade dysplasia components were microsatellite instability-high (in both the adenocarcinoma and high-grade dysplasia components). This suggests that microsatellite instability in the high-grade dysplasia component of duodenal adenoma is associated with progression to adenocarcinoma.

Prognosis and chemosensitivity of non-colorectal alimentary tract cancers with microsatellite instability

BACKGROUND

Data on outcomes of microsatellite instable and/or mismatch repair deficient (dMMR/MSI) digestive non-colorectal tumors are limited.

AIMS

To evaluate overall survival (OS) of patients with dMMR/MSI digestive non-colorectal tumor.

METHODS

All consecutive patients with a dMMR/MSI digestive non-colorectal tumor were included in this French retrospective multicenter study.

RESULTS

One hundred and sixteen patients were included with a mean age of 63.6 years and 32.6% with a Lynch syndrome. Most tumors were oesophago-gastric (54.3%) or small bowel (32.8%) adenocarcinomas and at a localized stage at diagnosis (86.7%). In patients with localized tumors and R0 resection, median OS was 134.0 ± 64.2 months. Median disease-free survival (DFS) was 100.3 ± 65.7 months. Considering oesophago-gastric tumors, median DFS was improved when chemotherapy was added to surgery (not reached versus 22.8 ± 10.0 months, p = 0.03). In patients with advanced tumors treated by chemotherapy, median OS was 14.2 ± 1.9 months and median progression-free survival was 7.4 ± 1.6 months.

CONCLUSION

dMMR/MSI digestive non-colorectal tumors are mostly diagnosed at a non-metastatic stage with a good prognosis. Advanced dMMR/MSI digestive non-colorectal tumors have a poor prognosis with standard chemotherapy.

Clinical practice guidelines for duodenal cancer 2021

Duodenal cancer is considered to be a small intestinal carcinoma in terms of clinicopathology. In Japan, there are no established treatment guidelines based on sufficient scientific evidence; therefore, in daily clinical practice, treatment is based on the experience of individual physicians. However, with advances in diagnostic modalities, it is anticipated that opportunities for its detection will increase in future. We developed guidelines for duodenal cancer because this disease is considered to have a high medical need from both healthcare providers and patients for appropriate management. These guidelines were developed for use in actual clinical practice for patients suspected of having non-ampullary duodenal epithelial malignancy and for patients diagnosed with non-ampullary duodenal epithelial malignancy. In this study, a practice algorithm was developed in accordance with the Minds Practice Guideline Development Manual 2017, and Clinical Questions were set for each area of epidemiology and diagnosis, endoscopic treatment, surgical treatment, and chemotherapy. A draft recommendation was developed through a literature search and systematic review, followed by a vote on the recommendations. We made decisions based on actual clinical practice such that the level of evidence would not be the sole determinant of the recommendation. This guideline is the most standard guideline as of the time of preparation. It is important to decide how to handle each case in consultation with patients and their family, the treating physician, and other medical personnel, considering the actual situation at the facility (and the characteristics of the patient).

Genetic analysis of Japanese patients with small bowel adenocarcinoma using next-generation sequencing

BACKGROUND

Small bowel adenocarcinomas (SBAs) are rare and there is little comprehensive data on SBA genomic alterations for Asian patients. This study aimed to profile genomic alterations of SBA in Japanese patients using targeted next-generation sequencing (NGS).

METHODS

We examined 22 surgical resections from patients with primary SBA. SBA genomic alterations were analyzed by NGS. Mismatch repair (MMR) status was determined by immunohistochemical analysis. Mucin phenotypes were classified as gastric (G), intestinal (I), gastrointestinal (GI), and null (N) types on MUC2, MUC5AC, MUC6, and CD10 immunostaining.

RESULTS

The most common genomic alterations found in SBA tumors were TP53 (n = 16), followed by KRAS (n = 6), APC (n = 5), PIK3CA (n = 4), CTNNB1 (n = 3), KIT (n = 2), BRAF (n = 2), CDKN2A (n = 2), and PTEN (n = 2). Deficient MMR tumors were observed in 6 out of 22 patients. Tumor mucin phenotypes included 2 in G-type, 12 in I-type, 3 in GI-type, and 5 in N-type. APC and CTNNB1 mutations were not found in G-type and GI-type tumors. KRAS mutations were found in all tumor types except for G-type tumors. TP53 mutations were found in all tumor types. Although no single gene mutation was associated with overall survival (OS), we found that KRAS mutations were associated with significant worse OS in patients with proficient MMR tumors.

CONCLUSIONS

SBA genomic alterations in Japanese patients do not differ significantly from those reports in Western countries. Tumor localization, mucin phenotype, and MMR status all appear to impact SBA gene mutations.

Mixed adenoneuroendocrine carcinoma of the non-ampullary duodenum with mismatch repair deficiency: a rare case report

A non-ampullary duodenal mixed adenoneuroendocrine carcinoma (MANEC), consisting of a conventional adenocarcinoma and a neuroendocrine carcinoma (NEC), is exceedingly rare. Moreover, mismatch repair (MMR) deficient tumors have recently attracted attention. The patient, a 75-year-old woman with epigastric pain and nausea, was found to have a type 2 tumor of the duodenum, which was diagnosed on biopsy as a poorly differentiated carcinoma. A pancreaticoduodenectomy specimen showed a well-defined 50 × 48 mm tumor in the duodenal bulb, which was morphologically composed of glandular, sheet-like, and pleomorphic components. The glandular component was a tubular adenocarcinoma, showing a MUC5AC-positive gastric type. The sheet-like component consisted of homogenous tumor cells, with chromogranin A and synaptophysin diffusely positive, and a Ki-67 index of 72.8%. The pleomorphic component was diverse and prominent atypical tumor cells proliferated, focally positive for chromogranin A, diffusely positive for synaptophysin, and the Ki-67 index was 67.1%. The sheet-like and pleomorphic components were considered NEC, showing aberrant expression of p53, retinoblastoma, and p16. Notably, all three components were deficient in MLH1 and PMS2. We diagnosed a non-ampullary duodenal MANEC with MMR deficiency. This tumor has a unique morphology and immunohistochemical profile, and is valuable for clarifying the tumorigenesis mechanism of a non-ampullary duodenal MANEC.

An artificial neural network model based on DNA damage response genes to predict outcomes of lower-grade glioma patients

Although the prognosis of lower-grade glioma (LGG) patients is better than others, outcomes are highly heterogeneous. Isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion status can identify patient subsets with different prognosis. However, in the era of precision medicine, there is still a lack of biomarkers that can accurately predict the individual prognosis of each patient. In this study, we found that most DNA damage response (DDR) genes were aberrantly expressed in LGG patients and were associated with their prognosis. Consequently, we developed an artificial neural network (ANN) model based on DDR genes to predict outcomes of LGG glioma patients. Then, we validated the predictive ability in an independent external dataset and found that the concordance indexes and area under time-dependent receiver operating characteristic curves of the predict index (PI) calculated based on the model were superior to those of the mutation markers. Subgroup analyses demonstrated that the model could accurately identify patients with the same mutation status but different prognosis. Moreover, the model can also identify patients with favorable prognostic mutation status but poor prognosis or vice versa. Finally, we also found that the PI was associated with the mutation status and with the altered immune microenvironment. These results demonstrated that the ANN model can accurately predict outcomes of LGG patients and will contribute to individualized therapies. In addition, a web-based application program for the model was developed.

Prognostic Role of Mismatch Repair Status, Histotype and High-Risk Pathologic Features in Stage II Small Bowel Adenocarcinomas

BACKGROUND

Small bowel adenocarcinoma is a relatively rare cancer, often diagnosed in an advanced stage. In localized and resectable disease, surgery alone or in combination with adjuvant chemotherapy is the mainstay of treatment. In the recently published National Comprehensive Cancer Network Clinical Practice guidelines, criteria for selecting patients with stage II small bowel adenocarcinoma to receive adjuvant chemotherapy are provided, and they are mainly extrapolated from studies on colorectal cancer.

PATIENTS AND METHODS

In the present study, we aimed to verify whether mismatch repair deficiency phenotype, high-risk pathologic features (including T4, positive resection margins and a low number of lymph nodes harvested), as well as tumor histologic subtype, were associated with cancer-specific survival in 66 stage II non-ampullary small bowel adenocarcinoma patients, collected through the Small Bowel Cancer Italian Consortium. A central histopathology review was performed. Mismatch repair deficiency was tested by immunohistochemistry for MLH1, MSH2, MSH6 and PMS2, and confirmed by polymerase chain reaction for microsatellite instability.

RESULTS

We identified mismatch repair deficiency, glandular/medullary histologic subtype, and celiac disease as significant predictors of favorable cancer-specific survival using univariable analysis with retained significance in bivariable models adjusted for pT stage. Among the high-risk features, only T4 showed a significant association with an increased risk of death; however, its prognostic value was not independent of mismatch repair status.

CONCLUSIONS

Mismatch repair protein expression, histologic subtype, association with celiac disease, and, in the mismatch repair proficient subset only, T stage, may help identify patients who may benefit from adjuvant chemotherapy.

Small Bowel Adenocarcinomas Featuring Special AT-Rich Sequence-Binding Protein 2 (SATB2) Expression and a Colorectal Cancer-Like Immunophenotype: A Potential Diagnostic Pitfall

Simple Summary

Since small bowel adenocarcinoma may mimic a colorectal primary neoplasm histologically, it is pivotal to find biomarkers to discriminate these two biologically distinct neoplasms. The aim of our study was to evaluate the expression of special AT-rich sequence-binding protein 2 (SATB2), expressed in the vast majority of colorectal carcinomas, and other gastrointestinal phenotypic markers, such as cytokeratin 7, cytokeratin 20 and caudal type homeobox 2 (CDX2), in 100 small bowel adenocarcinomas. We identified 20 SATB2-positive small bowel adenocarcinomas, including nine sporadic cancers, seven celiac disease-associated cancers and four Crohn’s disease-associated small bowel adenocarcinomas. Six small bowel adenocarcinomas, including two cases associated with celiac disease and four sporadic, displayed a full colorectal carcinoma-like immunoprofile. Unlike SATB2, cytokeratin patterns stratified small bowel adenocarcinoma patient prognosis. The small bowel should be considered as one of the possible sites of origin in cancers of unknown primary, even when the neoplasm shows a colorectal carcinoma-like immunoprofile.

Abstract

Special AT-rich sequence-binding protein 2 (SATB2) is a transcription factor expressed by colonic cryptic epithelium and epithelial neoplasms of the lower gastrointestinal (GI) tract, as well as by small bowel adenocarcinomas (SBAs), though at a lower rate. Nevertheless, up to now, only small SBA series, often including a very limited number of Crohn’s disease-associated SBAs (CrD-SBAs) and celiac disease-associated SBAs (CD-SBA), have been investigated for SATB2 expression. We evaluated the expression of SATB2 and other GI phenotypic markers (cytokeratin (CK) 7 and CK20, caudal type homeobox 2 (CDX2) and alpha-methylacyl-CoA racemase (AMACR)), as well as mismatch repair (MMR) proteins, in 100 SBAs, encompassing 34 CrD-SBAs, 28 CD-SBAs and 38 sporadic cases (Spo-SBAs). Any mutual association and correlation with other clinico-pathologic features, including patient prognosis, were searched. Twenty (20%) SATB2-positive SBAs (4 CrD-SBAs, 7 CD-SBAs and 9 Spo-SBAs) were identified. The prevalence of SATB2 positivity was lower in CrD-SBA (12%) in comparison with both CD-SBAs (25%) and Spo-SBAs (24%). Interestingly, six SBAs (two CD-SBAs and four Spo-SBAs) displayed a full colorectal carcinoma (CRC)-like immunoprofile (CK7−/CK20+/CDX2+/AMACR+/SATB2+); none of them was a CrD-SBA. No association between SATB2 expression and MMR status was observed. Although SATB2-positive SBA patients showed a more favorable outcome in comparison with SATB2-negative ones, the difference did not reach statistical significance. When cancers were stratified according to CK7/CK20 expression patterns, we found that CK7−/CK20- SBAs were enriched with MMR-deficient cases (71%) and patients with CK7−/CK20− or CK7−/CK20+ SBAs had a significantly better survival rate compared to those with CK7+/CK20− or CK7+/CK20+ cancers (p = 0.002). To conclude, we identified a small (6%) subset of SBAs featuring a full CRC-like immunoprofile, representing a potential diagnostic pitfall in attempts to identify the site of origin of neoplasms of unknown primary site. In contrast with data on colorectal carcinoma, SATB2 expression is not associated with MMR status in SBAs. CK patterns influence patient survival, as CK7−/CK20− cancers show better prognosis, a behavior possibly due to the high rate of MMR-deficient SBAs within this subgroup.

Remodeling of the ARID1A tumor suppressor

In recent years, AT-rich interactive domain-containing protein 1A (ARID1A) has been widely accepted as a bona fide tumor suppressor due to its essential role in preventing tumorigenesis and tumor progression in both mouse and human contexts. ARID1A shows high mutation frequencies in both cancers and preneoplastic lesions. The loss of ARID1A expression in cancer cells leads to increases in cell proliferation, invasion and migration and reductions in cell apoptosis and chemosensitivity. The tumor-suppressive role of ARID1A is mainly attributed to its regulation of gene transcription, which can be induced either directly by chromatin remodeling or indirectly by affecting histone modifications. ARID1A also acts independently of its cardinal transcription-regulating mechanisms, which include interfering with protein-protein interactions. Interestingly, nonmutational mechanisms, such as regulation by DNA hypermethylation, microRNAs, and ubiquitinases/deubiquitinases, have provided another perspective on ARID1A inactivation in cancer. Since the critical tumor-suppressive role of ARID1A has been revealed, several studies have attempted to identify synthetic lethal targets with ARID1A mutation/inactivation as an alternative strategy for cancer treatment.

Adenoma-like adenocarcinoma: clinicopathologic characterization of a newly recognized subtype of colorectal carcinoma

The 5th edition of the World Health Organization (WHO) Classification of Tumours (Digestive System) recognizes a new subtype of colorectal adenocarcinoma, called adenoma-like adenocarcinoma. In this study, we sought to determine its clinicopathologic associations and how it is comparable with adenocarcinoma, of no special type (NOS). We retrospectively reviewed all available archival slides of stage I-III colonic adenocarcinoma resection specimens at our institution from 2013 to 2016.Ninety-one cases were classified as adenoma-like adenocarcinoma, and 251 cases were classified as adenocarcinoma, NOS. Of the adenoma-like adenocarcinoma cases, a majority (65 cases, 71%) were composed exclusively of adenoma-like features, designated as pure adenoma-like adenocarcinoma, whereas in the rest, the component of adenoma-like morphology was more than 50% but less than 100%, designated as mixed adenoma-like adenocarcinoma. Compared with adenocarcinoma, NOS, adenoma-like adenocarcinoma cases were significantly associated with the absence of tumor budding (P < 0.001), the absence of an immature/myxoid desmoplastic reaction (P < 0.001), the presence of intraepithelial tumor-infiltrating lymphocytes (P = 0.006), involvement of fewer lymph nodes ( P < 0.001), fewer tumor deposits (P = 0.042), lower pT stage (P = 0.047), lower pN stage (P < 0.001), and consequently the pTNM prognostic group (P < 0.001), as well as better recurrence-free survival (RFS), as per univariate analysis than adenocarcinoma, NOS cases (P = 0.026) but not as per multivariate analysis. However, mixed adenoma-like adenocarcinoma had a worse RFS than pure adenoma-like adenocarcinoma (hazard ratio = 1.639, 95% confidence interval = 0.494-5.437). Our findings not only support the importance of distinguishing this new subtype of colorectal adenocarcinoma but also raise the question whether mixed adenoma-like adenocarcinoma cases should be included in this category, and if so, whether 50% is an appropriate cutoff, as currently defined by the WHO.

Intraepithelial tumour infiltrating lymphocytes are associated with absence of tumour budding and immature/myxoid desmoplastic reaction, and with better recurrence-free survival in stages I-III colorectal cancer

AIMS

Tumour budding (TB), desmoplastic reaction (DR) and intraepithelial tumour infiltrating lymphocytes (iTILs) are recently recognised prognostic factors in colorectal cancer (CRC). In this study, we evaluated their significance and relationship to each other and their cumulative effect on survival.

METHODS AND RESULTS

A total of 372 stages I-III CRC cases from 2013 to 2016 were included. Low TB was identified in 302 (81%) cases, immature/myxoid DR in 67 (18%) cases and iTILs in 130 (35.0%) cases. iTILs was associated with low budding (P = 0.0247), non-myxoid DR (P = 0.0004), poorly differentiated histology (P = 0.0015), absence of perineural invasion (P = 0.0367) and loss of mismatch repair proteins (P = 0.0002). Absence of iTILs and presence of immature/myxoid DR were associated with a worse recurrence-free survival (RFS) [hazard ratio (HR) = 2.191, 95% confidence interval (CI) = 1.232-3.895; and HR = 5.706, 95% CI = 3.632-8.964, respectively]. A competing risk analysis showed statistically significant prognostic groups combining iTILs and TB (P < 0.0001). Cases with iTILs and low TB were associated with better RFS compared to cases without iTILs and with intermediate/high TB (HR = 0.214, 95% CI = 0.109-0.421). Similarly, combining iTILs and DR revealed statistically significant prognostic groups (P < 0.0001). Cases with iTILs and a non-myxoid DR had better RFS compared to cases without iTILs and immature/myxoid DR (HR = 0.113, 95% CI = 0.056-0.230). On multivariate cause-specific analysis, patients' age (P = 0.0045), iTILs (P = 0.0345), DR (P < 0.0001) and pTNM prognostic groups (P < 0.0001) were associated with RFS.

CONCLUSIONS

Our study validates the association of iTILs and DR as independent prognostic finding in CRC, and propose a prognostic model using the combinations of iTILs with TB and stromal reaction in CRC.

Clinicopathologic determinants of pathologic treatment response in neoadjuvant treated rectal adenocarcinoma

Neoadjuvant treatment (NAT) followed by total mesorectal excision is currently considered the standard of treatment for rectal adenocarcinoma. The degree of pathologic treatment response (pTR) correlates significantly with the recurrence free survival and overall survival (OS). However, it remains unclear which clinical and pathologic factors are associated with a more robust response to NAT, including showing pathologic complete response (pCR). Chemokine receptor 4 (CXCR4) overexpression has been associated with unfavorable OS in some studies. In this study, we sought to evaluate the clinicopathologic determinants of pTR in neoadjuvant treated rectal adenocarcinoma (NAT-RA). We retrospectively identified 91 patients who underwent pre-treatment diagnostic biopsy, NAT, and surgical resection at our institution. The archival slides were reviewed for pathologic features in the pre-treatment biopsies and for assessment of pTR in the resection specimens according to the current College of American Pathologist (CAP)'s guidelines. pCR was obtained in 16.5% of the cases, whereas 20.9% had near pCR, 30.8% had partial response, and 31.9% had a poor/no response. CXCR4 immunohistochemical analysis was also performed on the pre-treatment biopsies. Lower pre-treatment cT-stage (p = 0.019) and pre-treatment AJCC cTNM stage groups (p = 0.004), longer time interval between completion of NAT and resection (p = 0.022), and presence of tumor-infiltrating lymphocytes in the pre-treatment biopsies (p = 0.019) were significantly associated with a better pTR. CXCR4 nuclear expression was associated with a lower percentage of residual tumor (p = 0.036). Pre-treatment CEA levels, tumor differentiation, CAP treatment response groups and lower percentage of residual tumor were associated with a better OS.

Loss of ARID1A expression is associated with DNA mismatch repair protein deficiency and favorable prognosis in advanced stage surgically resected esophageal adenocarcinoma

Esophageal adenocarcinoma often presents at an advanced stage and has a dismal prognosis. Current prognostic markers have limited utility. ARID1A is implicated as a tumor suppressor gene in esophageal adenocarcinoma. Loss of ARID1A expression correlates with DNA mismatch repair (MMR) protein deficiency in other tumors. We hypothesized that ARID1A loss is associated with prognosis and DNA MMR protein deficiency in esophageal adenocarcinoma. Tissue microarrays representing 316 surgically resected esophageal adenocarcinomas without neoadjuvant treatment were evaluated for ARID1A and MMR proteins by immunohistochemistry. Loss of ARID1A expression (ARID1A-loss) was detected in 41 of 316 (13%) adenocarcinomas. MMR deficiency was identified in 5% (17/316) but was detected more frequently in ARID1A-loss adenocarcinomas (13/41, 32%) than in ARID1A-retained adenocarcinomas (4/275, 1%; P < .001). Morphologically, ARID1A-loss adenocarcinomas frequently demonstrated peritumoral lymphoid aggregates (90%) and tumor infiltrating lymphocytes (51%). In patients with locally advanced or metastatic disease (stages III or IV, N = 169), patients with ARID1A-loss adenocarcinomas (N = 22) had longer overall survival than patients with ARID1A-retained adenocarcinomas (median [month]: 26 vs. 16, P = .010). In these patients, ARID1A-loss correlated with a 56% reduction in mortality independent of other prognostic factors (P = .007). In summary, loss of ARID1A expression is associated with DNA MMR protein deficiency in esophageal adenocarcinoma. Furthermore, ARID1A loss is independently associated with a more favorable prognosis for patients with locally advanced or metastatic esophageal adenocarcinomas.