Diagnostic Challenges Caused by Endoscopic Biopsy of Colonic Polyps: A Systematic Evaluation of Epithelial Misplacement With Review of Problematic Polyps From the Bowel Cancer Screening Program, United Kingdom. Am J Surg Pathol. 2016;40:1075-1083. [PMID: 26975041 DOI: 10.1097/pas.0000000000000641]

Hot avulsion versus argon plasma coagulation for the management of the non-ensnarable polyp: A multicenter, randomized controlled trial

Background and Aim

Snare resection of nonlifting colonic lesions often requires supplemental techniques. We compared the success rates of neoplasia eradication using hot avulsion and argon plasma coagulation in colonic polyps when complete snare polypectomy had failed.

Methods

Polyps that were not completely resectable by snare polypectomy were randomized to argon plasma coagulation or hot avulsion for completion of resection. Argon plasma coagulation was delivered using a forward shooting catheter, using a nontouch technique (flow 1.2 L, 35 watts). Hot avulsion was performed by grasping the neoplastic tissue with hot biopsy forceps and applying traction away from the bowel wall while using EndoCut I or soft coagulation for avulsion. Surveillance colonoscopies were performed at 6, 12, and 18 months.

Results

From November 2013 to July 2017, 59 patients were randomized to argon plasma coagulation (28) or hot avulsion (31). The median age was 69 (60-75), with 46% being female. The median residual tissue size was 10 mm (6-12). The residual adenoma rate at 6 months (hot avulsion 6% vs argon plasma coagulation 21% P = 0.09) and 18 months was not different between the groups (6.6% vs 3.6% P = 0.25). One patient in the argon plasma coagulation arm was diagnosed with metastatic cancer of likely colorectal origin despite benign histology in the original polypectomy specimen, supporting the importance of tissue acquisition.

Conclusion

Both hot avulsion and argon plasma coagulation are effective and safe modalities to complete resection of non-ensnarable colonic polyps.

Sporadic Polyps of the Colorectum

Colorectal polyps are common, and their diagnosis and classification represent a major component of gastrointestinal pathology practice. The majority of colorectal polyps represent precursors of either the chromosomal instability or serrated neoplasia pathways to colorectal carcinoma. Accurate reporting of these polyps has major implications for surveillance and thus for cancer prevention. In this review, we discuss the key histologic features of the major colorectal polyps with a particular emphasis on diagnostic pitfalls and areas of contention.

Lymphoglandular Complex-Like Colorectal Carcinoma-A Series of 20 Colorectal Cases, Including Newly Reported Features of Malignant Behavior

Distinguishing colon carcinoma that is surrounded by well-circumscribed lymphoid tissue from adenomas involving lymphoglandular complexes can be difficult. We assessed a multi-institutional international cohort of 20 colorectal carcinomas with associated prominent lymphoid infiltrates, which we referred to as lymphoglandular complex-like carcinoma (LGCC). We collected clinical and endoscopic features, including lesion size, endoscopic appearance, location, procedure, follow-up, AJCC stage, and mismatch repair status. We recorded the presence of the following histologic features: haphazard gland distribution, gland angulation, gland fusion, solid nest formation, single-cell formation, stromal desmoplasia, presence of lymphovascular invasion and perineural invasion, presence of lamina propria, cytologic atypia as low- or high-grade, presence of goblet cells in the invasive component, and the presence of a surface lesion. Most cases (9 of 13) were described endoscopically as sessile polyps with an average size of 1.56 cm. Most cases (90%) were associated with a surface lesion, of which the majority were tubular adenomas, though a subset was associated with sessile serrated lesions with dysplasia (3 of 18). All cases of LGCC demonstrated haphazard gland distribution and either gland angulation, fusion, or solid nest formation. A portion of cases demonstrated single-cell infiltration (35%) and desmoplasia (50%), and rarely lymphovascular invasion was present (5%). A subset (10%) of cases invaded beyond the submucosa. Deficient mismatch repair was present in 22% (2 of 9) of cases for which it was performed. In cases of colectomy or completion colectomy, nodal metastasis was present in 38% (3 of 8). No cases demonstrated disease recurrence or disease-specific mortality. Overall, LGCC represents an enigmatic subset of carcinomas that is important to distinguish from adenomas involving lymphoglandular complexes due to its varying prognostic outcomes.

Desmin immunostaining is effective for improving interobserver variability in the depth assessment of the submucosal invasion of colorectal cancers

Tumor depth evaluation is essential for pathological tumor staging because it affects clinical management as an independent risk factor for lymph node metastasis in colorectal cancers. However, poor interobserver variability of invasion depth has been reported. This study aimed to clarify the effectiveness of desmin immunostaining in the histological diagnosis of colorectal cancer. Overall, 63 sets of slides of colorectal cancer stained with hematoxylin and eosin (H&E) and desmin were prepared and independently reviewed by four examiners. After reviewing the desmin-stained slides, the interobserver variability of H&E slides alone was significantly improved for all examiners. For the assessment of Tis vs. T1, the sensitivity and accuracy were significantly improved for all examiners by combining H&E and desmin immunostaining. For the diagnosis of T1b vs. Tis or T1a, specificity and accuracy were significantly improved by adding desmin immunostaining. Ancillary desmin staining to assess submucosal invasion in colorectal cancers significantly improved interobserver agreement, led to efficient screening of T1 cancers, and reduced excessive T1b diagnoses. The combination of desmin immunostaining and H&E staining is highly recommended for diagnosing invasive colorectal cancer.

Rectal tubular adenoma with submucosal pseudoinvasion misdiagnosed as adenocarcinoma: A case report

BACKGROUND

Differential diagnosis of colorectal intramucosal tumors from invasive adenocarcinoma is important in clinical practice due to the different risks of lymph node metastasis and different treatment options. The phenomenon of a colorectal adenoma with part of the gland entering the submucosa is known as pseudoinvasion of the adenoma, which is a major challenge for pathological diagnosis. It is essential to raise awareness of colorectal adenoma with submucosal pseudoinvasion clinically to avoid overtreatment.

CASE SUMMARY

We describe a case of rectal adenoma with submucosal pseudoinvasion in a 48-year-old man. The patient was admitted to Jinhua People's Hospital due to a change in stool habit for 5 d. We performed colonoscopy, and the results suggested a submucosal bulge approximately 1.0 cm × 1.0 cm in size in the rectum 8 cm from the anal verge, with red surface erosion. Ultrasound colonoscopy was also performed and a homogeneous hypoechoic mass about 0.52 cm × 0.72 cm in size was seen at the lesion, protruding into the lumen with clear borders and invading the submucosa. Endoscopic surgery was then performed and the pathological specimen showed a tubular adenoma with high-grade intraepithelial neoplasia (intramucosal carcinoma) involving the adenolymphatic complex. In addition, we performed a literature review of rectal tubular adenoma with submucosal pseudoinvasion to obtain a deeper understanding of this disease.

CONCLUSION

The aim of this study was to improve awareness of this lesion for clinicians and pathologists to reduce misdiagnosis.

Infrared Spectroscopic Analysis in the Differentiation of Epithelial Misplacement From Adenocarcinoma in Sigmoid Colonic Adenomatous Polyps

Purpose

The differential diagnosis of epithelial misplacement from invasive cancer in the colon is a challenging endeavour, augmented by the introduction of bowel cancer population screening. The main aim of the work is to test, as a proof-of concept study, the ability of the infrared spectroscopic imaging approach to differentiate epithelial misplacement from adenocarcinoma in sigmoid colonic adenomatous polyps.

Methods

Ten samples from each of the four diagnostic groups, normal colonic mucosa, adenomatous polyps with low grade dysplasia, epithelial misplacement in adenomatous polyps and adenocarcinoma, were analysed using IR spectroscopic imaging and data processing methods. IR spectral images were subjected to data pre-processing and cluster analysis based segmentation to identify epithelial, connective tissue and stromal regions. Statistical analysis was carried out using principal component analysis and linear discriminant analysis based cross validation, to classify spectral features according to the pathology, and the diagnostic attributes were compared.

Results

The combined 4-group classification model on an average showed a sensitivity of 64%, a specificity of 88% and an accuracy of 76% for prediction based on a 'single spectrum', whilst a 'majority-vote' prediction on an average showed a sensitivity of 73%, a specificity of 90% and an accuracy of 82%. The 2-group model, for the differential diagnosis of epithelial misplacement versus adenocarcinoma, showed an average sensitivity and specificity of 82.5% for prediction based on a 'single spectrum' whilst a 'majority-vote' classification showed an average sensitivity and specificity of 90%. A 92% area under the curve (AUC) value was obtained when evaluating the classifier using the Receiver Operating Characteristics (ROC) curves.

Conclusions

IR spectroscopy shows promise in its ability to differentiate epithelial misplacement from adenocarcinoma in tissue sections, considered as one of the most challenging endeavours in population-wide diagnostic histopathology. Further studies with larger series, including cases with challenging diagnostic features are required to ascertain the capability of this modern digital pathology approach. In the long-term, IR spectroscopy based pathology which is relatively low-cost and rapid, could be a promising endeavour to consider for integration into the existing histopathology pathway, in particular for population based screening programmes where large number of samples are scrutinised.

Compliance with mismatch repair testing in pT1 colorectal cancer diagnosed before the age of 70 years

Mismatch repair (MMR) testing is recommended in the Netherlands for all patients under 70 years of age with newly diagnosed colorectal cancer (CRC) in order to identify Lynch syndrome. T1 CRC can be removed by local excision or oncological surgical resection. We evaluated the frequency of MMR testing in pT1 lesions within the Dutch CRC screening cohort. pT1 CRC diagnosed within the Dutch population-based screening program from 2016-2018 were identified by the Dutch pathology registry (PALGA). Pathology reports were evaluated, including registration of MMR testing (by immunohistochemistry and/or microsatellite instability PCR). Frequency of MMR testing was compared between pT1 tumors that were treated by local (endoscopic or transanal) excision and oncological surgical resections. A total of 3.692 pT1 CRCs were diagnosed (median age 63 years, 61.4% males). MMR testing was performed in 83% and uptake increased over time (71% in 2016 to 92% in 2018, p<0.01). MMR testing was significantly more often performed in younger patients and in academic hospitals. When pT1 CRC was treated by oncological surgical resection (n=1.132), MMR testing was performed in 89% of cases and was known prior to oncological resection in 51% of cases. MMR testing occurred significantly less often in case of local excision (80% of n=2.560) compared to oncological surgical resection (p<0.01). MMR testing was performed in 83% of T1 CRCs and uptake increased over time. MMR testing was more frequently performed in pT1 CRC resected by oncological surgical resection compared with local excision.

Colorectal epithelial neoplasm associated with gut-associated lymphoid tissue

BACKGROUND

Colorectal epithelial neoplasm extending into the submucosal gut-associated lymphoid tissue (GALT) can cause difficulties in the differential diagnosis. Regarding GALT-associated epithelial neoplasms, a few studies favor the term "GALT carcinoma" while other studies have mentioned the term "GALT-associated pseudoinvasion/epithelial misplacement (PEM)".

METHODS

The clinicopathologic characteristics of 11 cases of colorectal epithelial neoplasm associated with submucosal GALT diagnosed via endoscopic submucosal dissection were studied.

RESULTS

Eight cases (72.7%) were in males. The median age was 59 years, and age ranged from 53 to 73. All cases had a submucosal tumor component more compatible with GALT-associated PEM. Eight cases (72.7%) were located in the right colon. Ten cases (90.9%) had a non-protruding endoscopic appearance. Nine cases (81.8%) showed continuity between the submucosal and surface adenomatous components. Nine cases showed (81.8%) focal defects or discontinuation of the muscularis mucosae adjacent to the submucosal GALT. No case showed hemosiderin deposits in the submucosa or desmoplastic reaction. No case showed single tumor cells or small clusters of tumor cells in the submucosal GALT. Seven cases (63.6%) showed goblet cells in the submucosa. No cases showed oncocytic columnar cells lining submucosal glands.

CONCLUSIONS

Our experience suggests that pathologists should be aware of the differential diagnosis of GALT-associated submucosal extension by colorectal adenomatous neoplasm. Further studies are needed to validate classification of GALT-associated epithelial neoplasms.

How to measure tumour response in rectal cancer? An explanation of discrepancies and suggestions for improvement

Various methods categorize tumour response after neoadjuvant therapy, including down-staging and tumour regression grading. Response categories allow comparison of different treatments within clinical trials and predict outcome. A reproducible response categorization could identify subgroups with high or low risk for the most appropriate subsequent treatments, like watch and wait. Lack of standardization and interpretation difficulties currently limit the usability of these approaches. In this review we describe these difficulties for the evaluation of chemoradiation in rectal cancer. An alternative approach of tumour response is based on patterns of residual disease, including fragmentation. We summarise the evidence behind this alternative method of response categorisation, which explains a number of very relevant clinical discrepancies. These issues include differences between downstaging and tumour regression, high local regrowth in advanced tumours during watchful waiting procedures, the importance of resection margins, the limited value of post-treatment biopsies and the relatively poor outcome of patients with a near complete pathological response. Recognition of these patterns of response can allow meaningful development of novel biomarkers in the future.

Colonic Adenomatous Polyps Involving Submucosal Lymphoglandular Complexes: A Diagnostic Pitfall

Lymphoglandular complexes (LGCs) are lymphoid nodules containing intestinal mucosa, present in close apposition to muscularis mucosae or submucosa. Rarely, colorectal adenomas involve submucosal LGCs, simulating invasive adenocarcinoma with associated submucosal lymphoid aggregates, and presenting a diagnostic pitfall. We aimed to identify distinctive histologic features between submucosal LGCs and true invasion. Seven adenomas (tubular/tubulovillous adenomas [n=6], including 4 with high-grade dysplasia and 1 with focal intramucosal adenocarcinoma, and sessile serrated adenoma [n=1]) were in the right (n=5) and left colon (n=2). Seven adenocarcinomas were in the right (n=3), left (n=2), and rectum/rectosigmoid colon (n=2). Adenomatous glands involving submucosal LGCs were invested in lamina propria, showed continuity with surface adenoma, were well rounded and contained within lymphoid tissue, and predominantly lacked classic features of "pseudoinvasion." One case showed a herniation pattern carrying muscularis mucosae. Adenocarcinomas had at least one of the following features: infiltrating single cells/small clusters (n=5), poorly formed, fused, and irregular glands (n=2), solid tumor nests (n=1), desmoplastic reaction (n=5), intraluminal necrosis (n=3), or lymphovascular invasion (n=1). In contrast, no adenoma had these features. Adenocarcinomas showed no herniation, but connection to surface tumor (n=5) was seen. Five invasive adenocarcinomas extended into the submucosa beyond the lymphoid aggregate. In conclusion, adenomas involving LGCs are a rare, clinicopathologically distinct form of pseudoinvasion that mimics invasive adenocarcinoma; histologic features that distinguish them are a well-rounded contour contained within the lymphoid tissue, and lack of infiltrating single cells/small clusters, poorly formed, fused, and irregular glands, solid tumor nests, desmoplastic reaction, and lymphovascular invasion.

Pedunculated Morphology of T1 Colorectal Tumors Associates With Reduced Risk of Adverse Outcome

BACKGROUND & AIMS

Risk stratification for adverse events, such as metastasis to lymph nodes, is based only on histologic features of tumors. We aimed to compare adverse outcomes of pedunculated vs nonpedunculated T1 colorectal cancers (CRC).

METHODS

We performed a retrospective study of 1656 patients diagnosed with T1CRC from 2000 through 2014 at 14 hospitals in The Netherlands. The median follow-up time of patients was 42.5 months (interquartile range, 18.5-77.5 mo). We evaluated the association between tumor morphology and the primary composite end point, adverse outcome, adjusted for clinical variables, histologic variables, resection margins, and treatment approach. Adverse outcome was defined as metastasis to lymph nodes, distant metastases, local recurrence, or residual tissue. Secondary end points were tumor metastasis, recurrence, and incomplete resection.

RESULTS

Adverse outcome occurred in 67 of 723 patients (9.3%) with pedunculated T1CRCs vs 155 of 933 patients (16.6%) with nonpedunculated T1CRCs. Pedunculated morphology was independently associated with decreased risk of adverse outcome (adjusted odds ratio [OR], 0.59; 95% CI, 0.42-0.83; P = .003). Metastasis, incomplete resection, and recurrence were observed in 5.8%, 4.6%, and 3.9% of pedunculated T1CRCs vs 10.6%, 8.0%, and 6.6% of nonpedunculated T1CRCs, respectively. Pedunculated morphology was independently associated with a reduced risk of metastasis (adjusted OR, 0.62; 95% CI, 0.41-0.94; P = .03), incomplete resection (adjusted OR, 0.57; 95% CI, 0.36-0.91; P = .02), and recurrence (adjusted hazard ratio, 0.52; 95% CI, 0.32-0.85; P = .009). Metastasis, incomplete resection, and recurrence did not differ significantly between low-risk pedunculated vs nonpedunculated T1CRCs (0.8% vs 2.9%, P = .38; 1.5% vs 0%, P = .99; 1.5% vs 0%; P = .99). However, incomplete resection and recurrence were significantly lower for high-risk pedunculated vs nonpedunculated T1CRCs (6.5% vs 12.5%; P = .007; 4.4% vs 8.6%; P = .03).

CONCLUSIONS

In a retrospective study of patients with T1CRC, we found pedunculated morphology to be associated independently with a decreased risk of adverse outcome in a T1CRC population at high risk of adverse outcome. Incorporating morphologic features of tumors in risk assessment could help predict outcomes of patients with T1CRC and help identify the best candidates for surgery.

Diagnostic and reporting issues of preneoplastic polyps of the large intestine with early carcinoma

Premalignant polyps of the large intestine are common specimens in surgical pathology. They consist of several different subtypes identifiable by histological criteria that are associated with different molecular characteristics and with the development of different types of colorectal carcinoma. The most common of these is the conventional adenoma, which most commonly leads to carcinomas with a low degree of methylation (CIMP-L) that are microsatellite stable. In Lynch syndrome patients these polyps lead to CIMP-L carcinomas that are microsatellite instable. The second most common is the sessile serrated adenoma, which leads to carcinomas with a high degree of methylation (CIMP-H) that may be either microsatellite stable or instable. The least common premalignant polyp is the traditional serrated adenoma, which can lead to either CIMP-L or CIMP-H carcinomas, most often microsatellite stable. This paper will review the histological features of these lesions, discuss problems in diagnosis and discuss the role of histology in management.

Current strategies for malignant pedunculated colorectal polyps

Despite significant advances in imaging techniques, the incidence of colorectal cancer has been increasing in recent years, with many cases still being diagnosed in advanced stages. Early detection and accurate staging remain the main factors that lead to a decrease in the cost and invasiveness of the curative techniques, significantly improving the outcome. However, the diagnosis of pedunculated early colorectal malignancy remains a current challenge. Data on the management of pedunculated cancer precursors, apart from data on nonpolypoid lesions, are still limited. An adequate technique for complete resection, which provides the best long-term outcome, is mandatory for curative intent. In this context, a discussion regarding the diagnosis of malignancy of pedunculated polyps, separate from non-pedunculated variants, is necessary. The purpose of this review is to provide a critical review of the most recent literature reporting the different features of malignant pedunculated colorectal polyps, including diagnosis and management strategies.

Bioinformatics Analysis Reveals Most Prominent Gene Candidates to Distinguish Colorectal Adenoma from Adenocarcinoma

Colorectal cancer (CRC) is one of the leading causes of death by cancer worldwide. Bowel cancer screening programs enable us to detect early lesions and improve the prognosis of patients with CRC. However, they also generate a significant number of problematic polyps, e.g., adenomas with epithelial misplacement (pseudoinvasion) which can mimic early adenocarcinoma. Therefore, biomarkers that would enable us to distinguish between adenoma with epithelial misplacement (pseudoinvasion) and adenoma with early adenocarcinomas (true invasion) are needed. We hypothesized that the former are genetically similar to adenoma and the latter to adenocarcinoma and we used bioinformatics approach to search for candidate genes that might be potentially used to distinguish between the two lesions. We used publicly available data from Gene Expression Omnibus database and we analyzed gene expression profiles of 252 samples of normal mucosa, colorectal adenoma, and carcinoma. In total, we analyzed 122 colorectal adenomas, 59 colorectal carcinomas, and 62 normal mucosa samples. We have identified 16 genes with differential expression in carcinoma compared to adenoma: COL12A1, COL1A2, COL3A1, DCN, PLAU, SPARC, SPON2, SPP1, SULF1, FADS1, G0S2, EPHA4, KIAA1324, L1TD1, PCKS1, and C11orf96. In conclusion, our in silico analysis revealed 16 candidate genes with different expression patterns in adenoma compared to carcinoma, which might be used to discriminate between these two lesions.

Problematic Colorectal Polyps: Is It Cancer and What Do I Need to Do About It?

Two issues commonly arise for pathologists reporting adenomatous polyps of the colorectum. Particularly problematic within large sigmoid colonic adenomas is the distinction between benign misplacement of epithelium into the submucosa and invasive malignancy. This distinction requires careful morphologic evaluation of key discriminatory features, assisted only rarely by the application of selected adjunctive immunohistochemistry. Following a diagnosis of adenocarcinoma within a polypectomy or other local excision specimen, systematic assessment is required of features that may indicate the risk of residual local and/or nodal neoplastic disease and inform management decision-making regarding the need for further endoscopic or surgical intervention.

Identifying and analyzing different cancer subtypes using RNA-seq data of blood platelets

Detection and diagnosis of cancer are especially important for early prevention and effective treatments. Traditional methods of cancer detection are usually time-consuming and expensive. Liquid biopsy, a newly proposed noninvasive detection approach, can promote the accuracy and decrease the cost of detection according to a personalized expression profile. However, few studies have been performed to analyze this type of data, which can promote more effective methods for detection of different cancer subtypes. In this study, we applied some reliable machine learning algorithms to analyze data retrieved from patients who had one of six cancer subtypes (breast cancer, colorectal cancer, glioblastoma, hepatobiliary cancer, lung cancer and pancreatic cancer) as well as healthy persons. Quantitative gene expression profiles were used to encode each sample. Then, they were analyzed by the maximum relevance minimum redundancy method. Two feature lists were obtained in which genes were ranked rigorously. The incremental feature selection method was applied to the mRMR feature list to extract the optimal feature subset, which can be used in the support vector machine algorithm to determine the best performance for the detection of cancer subtypes and healthy controls. The ten-fold cross-validation for the constructed optimal classification model yielded an overall accuracy of 0.751. On the other hand, we extracted the top eighteen features (genes), including TTN, RHOH, RPS20, TRBC2, in another feature list, the MaxRel feature list, and performed a detailed analysis of them. The results indicated that these genes could be important biomarkers for discriminating different cancer subtypes and healthy controls.

Squamoid morules in the pseudoinvasive foci of colonic polyp morphologically mimic invasive carcinoma

Colorectal adenomas can show focal squamous differentiation or squamoid morules. We describe histologic findings of squamoid morules in the pseudoinvasive foci of colorectal polyps mimicking invasive carcinoma. Five colonic polyps with squamoid morules in the pseudoinvasive foci were collected. Histologic review and immunostains for cytokeratin 5/6, p63, synaptophysin, and chromogranin were performed on cases with squamoid morules. Forty-seven consecutive colorectal polyps with pseudoinvasion, none of which showed squamoid morules by histology review, and their clinicopathologic features were compared with the cases containing squamoid morules. Cases with squamoid morules more frequently occurred in younger patients (P=.047) and were located in right colon (P=.027) than those without squamoid morules. Diagnosis of the polyps included tubular/tubulovillous adenoma with low-grade (with squamoid morules, n=3; versus without squamoid morules, n=29) or high-grade dysplasia (n=2 versus n=15) and sessile serrated adenoma (none versus n=3). Squamoid morules formed nodules protruding into the lumen of glandular structures or partially replaced adenomatous glands without forming a discrete nodule. They also presented as solid nests showing a well-formed morular structure around the bottom of adenomatous glands or myxoinflammatory stroma. Importantly, squamoid morules often formed a pseudocribriform or solid nest sitting in the stroma of pseudoinvasive foci. All cases (n=4) showed cytokeratin 5/6 positivity and p63 negativity in squamoid morules. Three and 1 of 4 cases showed focal positivity for synaptophysin and chromogranin, respectively, in squamoid morules. Squamoid morules in colonic adenomatous polyps can mimic invasive carcinoma when present in the pseudoinvasive foci. Pathologists should be aware of their presence.

Diagnosis of T1 colorectal cancer in pedunculated polyps in daily clinical practice: a multicenter study

T1 colorectal cancer can be mimicked by pseudo-invasion in pedunculated polyps. British guidelines are currently one of the few which recommend diagnostic confirmation of T1 colorectal cancer by a second pathologist. The aim of this study was to provide insights into the accuracy of histological diagnosis of pedunculated T1 colorectal cancer in daily clinical practice. A sample of 128 cases diagnosed as pedunculated T1 colorectal cancer between 2000 and 2014 from 10 Dutch hospitals was selected for histological review. Firstly, two Dutch expert gastrointestinal pathologists reviewed all hematoxylin-eosin stained slides. In 20 cases the diagnosis T1 colorectal cancer was not confirmed (20/128; 16%). The discordant cases were subsequently discussed with a third Dutch gastrointestinal pathologist and a consensus diagnosis was agreed. The revised diagnoses were pseudo-invasion in 10 cases (10/128; 8%), high-grade dysplasia in 4 cases (4/128; 3%), and equivocal in 6 cases (6/128; 5%). To further validate the consensus diagnosis, the discordant cases were reviewed by an independent expert pathologist from the United Kingdom. A total of 39 cases were reviewed blindly including the 20 cases with a revised diagnosis and 19 control cases where the Dutch expert panel agreed with the original reporting pathologists diagnosis. In 19 of the 20 cases with a revised diagnosis the British pathologist agreed that T1 colorectal cancer could not be confirmed. Additionally, amongst the 19 control cases the British pathologist was unable to confirm T1 colorectal cancer in a further 4 cases and was equivocal in 3 cases. In conclusion, both generalist and expert pathologists experience diagnostic difficulty distinguishing pseudo-invasion and high-grade dysplasia from T1 colorectal cancer. In order to prevent overtreatment, review of the histology of pedunculated T1 colorectal cancers by a second pathologist should be considered with discussion of these cases at a multidisciplinary meeting.