Survival outcomes used to validate version 9 of the American Joint Committee on Cancer staging system for appendiceal cancer.

The standard for cancer staging in the United States for all cancer sites, including primary carcinomas of the appendix, is the American Joint Committee on Cancer (AJCC) staging system. AJCC staging criteria undergo periodic revisions, led by a panel of site-specific experts, to maintain contemporary staging definitions through the evaluation of new evidence. Since its last revision, the AJCC has restructured its processes to include prospectively collected data because large data sets have become increasingly robust and available over time. Thus survival analyses using AJCC eighth edition staging criteria were used to inform stage group revisions in the version 9 AJCC staging system, including appendiceal cancer. Although the current AJCC staging definitions were maintained for appendiceal cancer, incorporating survival analysis into the version 9 staging system provided unique insight into the clinical challenges in staging rare malignancies. This article highlights the critical clinical components of the now published version 9 AJCC staging system for appendix cancer, which (1) justified the separation of three different histologies (non-mucinous, mucinous, signet-ring cell) in terms of prognostic variance, (2) demonstrated the clinical implications and challenges in staging heterogeneous and rare tumors, and (3) emphasized the influence of data limitations on survival analysis for low-grade appendiceal mucinous neoplasms.

Pseudomyxoma Peritonei Arising from Urachal Mucinous Neoplasms: a Case Series and Updated Literature Review.

To report a case series of patients with pseudomyxoma peritonei (PMP) from urachal mucinous neoplasm (UMN) treated with CRS and HIPEC at a high-volume referral centre, along with an updated literature review. Retrospective review of cases treated between 2000 and 2021. A literature review using MEDLINE and Google Scholar databases was performed. Clinical presentation of PMP from UMN is heterogeneous, and common symptoms are abdominal distension, weight loss, fatigue and haematuria. At least one tumour marker among CEA, CA 19.9, and CA 125 was elevated in the six cases reported, and 5/6 had a preoperative working diagnosis of urachal mucinous neoplasm suspected on detailed cross-sectional imaging. Complete cytoreduction was achieved in five cases, while one patient underwent maximal tumour debulking. Histological findings mirrored the findings of PMP from appendiceal mucinous neoplasms (AMN). Overall survival ranged between 43 and 141 months after complete cytoreduction. On literature review, 76 cases have been reported to date. Complete cytoreduction is associated with good prognosis for patients with PMP from UMN. A definitive classification system is still not available. Supplementary Information: The online version contains supplementary material available at 10.1007/s13193-022-01694-5.

Development and Validation of Nomograms to Predict Survival in Patients Undergoing Complete Cytoreduction and Hyperthermic Intraperitoneal Chemotherapy for Pseudomyxoma Peritonei of Appendiceal Origin.

Importance: Pseudomyxoma peritoni, a rare condition characterized by mucinous ascites and peritoneal deposits, mainly originates from a ruptured mucinous appendix tumor and is considered an indolent disease but can progress and become fatal. Optimal treatment to improve cure and survival rates involves complete cytoreductive surgery (CCRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). Accurate predictive models are useful in supporting and informing treatment strategies and stratifying patient follow-up. Objective: To evaluate the prognostic significance of clinically important variables and generate validated nomograms to predict overall (OS) and disease-free survival (DFS) following CCRS and hyperthermic intraperitoneal HIPEC for pseudomyxoma peritonei (PMP) of appendiceal origin. Design, Setting, and Participants: This retrospective study used prospectively collected data on patients who had cytoreductive surgery (CRS) and HIPEC in a single institution between 1994 and 2018. The cohort was randomly allocated into development (70%) and validation (30%) sets. Univariate and multivariate analyses were performed with Cox proportional hazards regression. Main Outcomes and Measures: A prediction model was developed with significant prognostic factors identified by multivariate analysis. The model's prognostic performance was evaluated with the concordance index (C index). The nomogram was calibrated by comparing the predicted and observed probabilities. Results: Of 2637 CRS and HIPEC operations, 1102 patients (female, 64.4%; median age [IQR], 57.0 [48.0-66.0] years) (41.8%) had CCRS for PMP of appendiceal origin. Elevated tumor markers, peritoneal carcinomatosis index, gastrectomy, and tumor grade were independent predictive factors for DFS. Gender, age, elevated tumor makers, peritoneal carcinomatosis index, and tumor grade influenced OS. The nomograms were generated with respective prognostic factors. The nomograms showed good performance in predicting survival. Median OS of the cohort was 16.5 years (95% CI, 13.7-19.2) with a 5-year probability of survival of 80.2%. The median DFS was 10.3 years (95% CI, 7.2- 13.3) and the 5-year probability of recurrence-free survival was 60.5%. Conclusions and Relevance: Clinically important independent predictors for survival and recurrence were selected to develop the nomograms for OS and DFS. These 2 nomograms are user friendly and useful tools for patient management with clinical trial design applications.

Fear of Cancer Recurrence in peritoneal malignancy patients following treatment: a cross-sectional study.

PURPOSE: To assess Fear of Cancer Recurrence (FCR)-its prevalence, trajectory, and relationship to several demographic and clinical characteristics, and quality of life-in a sample of peritoneal malignancy survivors, up to 5 years post-surgery. METHODS: The Fear of Cancer Recurrence Inventory-Short Form (FCRI-SF) and 36-Item Short-Form Health Survey (SF-36) were used to collect cross-sectional data from peritoneal malignancy survivors to assess their Fear of Cancer Recurrence and quality of life respectively as well as other demographic and clinical data. RESULTS: The results show that more than two-thirds of the participants (N = 301) experience severe/clinical FCR. FCR is relatively stable over time. Younger patients who are struggling with anxiety or depression or receiving professional mental health support at the time of the surgery are at a higher risk of FCR. FCR is associated with a worse quality of life. CONCLUSIONS: Peritoneal malignancy survivors are at a high risk of FCR, and it compromises their psychological, mental, and social well-being (quality of life). IMPLICATIONS FOR CANCER SURVIVORS: Raise awareness about the high risk of FCR in this population and the demographic and clinical factors that are associated with it. Encourage peritoneal malignancy services and health professionals to address FCR in this population by normalizing it and providing support for those struggling with it.

High-Grade Appendiceal Mucinous Neoplasm: Clinicopathologic Findings in 35 Cases.

CONTEXT.­: High-grade appendiceal mucinous neoplasm (HAMN) is a relatively recently introduced term describing a rare epithelial neoplasm of the appendix that demonstrates pushing-type invasion but high-grade cytologic atypia. It remains understudied. OBJECTIVE.­: To describe clinicopathologic features of HAMNs. DESIGN.­: We identified 35 HAMNs in a multi-institutional retrospective study. Clinical and histologic features were reviewed in all cases, as well as molecular features in 8 cases. RESULTS.­: Patients were 57 years of age on average and most commonly presented with abdominal/pelvic pain. Histologically, 57% of the tumors showed widespread high-grade features. Architectural patterns in high-grade areas included flat, undulating, or villous growth, and occasionally micropapillary, cribriform, or multilayered growth. Thirteen cases had intact serosa, and the remaining 22 perforated the serosa, including 7 with peritoneal acellular mucin beyond appendiceal serosa and 10 with grade 2 pseudomyxoma peritonei. Molecular abnormalities included KRAS mutations in 7 cases and TP53 mutations in 4. No tumor confined to the appendix recurred. Two patients without pseudomyxoma peritonei at initial presentation developed pseudomyxoma on follow-up. Among 11 patients who presented with pseudomyxoma peritonei, 5 died of disease and 3 were alive with disease at last follow-up. CONCLUSIONS.­: HAMNs have a similar presentation to low-grade appendiceal mucinous neoplasm, and similar stage-based prognosis. When they spread to the peritoneum, they typically produce grade 2 pseudomyxoma peritonei, which may be associated with a worse prognosis than classical grade 1 pseudomyxoma peritonei.

Fear of cancer recurrence in peritoneal malignancy patients following complete cytoreductive surgery (CCRS) and hyperthermic intraperitoneal chemotherapy (HIPEC): an observational study protocol.

INTRODUCTION: Fear of cancer recurrence (FCR) is correlated with higher depression levels, worse quality of life and increased utilisation of healthcare services. There is no research on FCR in peritoneal malignancy (PM) patients-a rare type of abdominal cancer. This study aims to explore the prevalence, trajectory, demographic and clinical characteristics that are associated with FCR and its relationship with quality of life in PM patients. METHODS AND ANALYSIS: This is a cross-sectional study. Validated measures will be used to collect data on the levels of FCR (Fear of Cancer Recurrence Inventory-Short Form) and quality of life (36-Item Short-Form Health Survey) of PM patients who have had surgery in the last 5 years at the Peritoneal Malignancy Institute in Basingstoke Hospital (minimum N=260). Descriptive statistics, Pearson χ2 tests and correlational tests will be used to analyse the data. ETHICS AND DISSEMINATION: Ethical approval was obtained from the HRA and Health and Care Research Wales (HCRW). The results of this study will be shared with the participants of this study, presented at conferences and PM patients' days in the form of presentations or posters, and published in a scientific journal. DISCUSSION: The results of this exploratory study will be used to inform a multicentre observational study to explore the effect of FCR on PM patients' mental health (depression and anxiety), quality of life and healthcare utilisation which will inform a multicentre randomised controlled trial to assess the effectiveness of using evidenced-based interventions to lower FCR in PM patients.

Overall Survival is More Closely Associated with Peritoneal than Primary Appendiceal Pathological Grade in Pseudomyxoma Peritonei with Discordant Pathology.

BACKGROUND: The WHO classification of mucinous appendix neoplasms and pseudomyxoma peritonei (PMP) describes low- and high-grade histology and is of prognostic importance. The metastatic peritoneal disease grade can occasionally be different from the primary appendix tumor. This analysis aimed to report outcomes from a high-volume center in patients with pathological discordance. METHODS: This was a retrospective analysis of prospective data of patients treated by cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) for PMP at a single institution between January 2016 and December 2020. Reporting was by pathologists with a special interest in peritoneal malignancy. Discordant pathology was classified as a low-grade primary appendix tumor with high-grade peritoneal disease, or a high-grade primary appendix tumor with low-grade peritoneal disease. Outcomes analyzed were overall and recurrence-free survival, and Kaplan-Meier survival curves and the log-rank test were used to analyze the outcomes. RESULTS: Between 2016 and 2020, 830 patients underwent CRS and HIPEC for PMP, of whom 37 (4.4%) had discordant pathology. The primary appendix tumors were low-grade in 23 patients and high-grade in 14 patients. The median Peritoneal Cancer Index (PCI) was significantly higher in patients with a low-grade primary tumor (31 vs. 16; p = 0.001), while complete cytoreduction (CC0/1) was achieved in 31/37 (83.8%) patients. The median follow-up was 19 months. Overall survival was worse in those with high-grade peritoneal disease (p = 0.029), whereas recurrence-free survival was similar in both groups (p = 0.075). CONCLUSION: In PMP with pathological discordance, the peritoneal disease grade influences prognosis and survival.

Role of immunohistochemistry for interobserver agreement of Peritoneal Regression Grading Score in peritoneal metastasis.

Pressurized intraperitoneal aerosol chemotherapy (PIPAC)-directed therapy is a new treatment option for peritoneal metastasis (PM). The 4-tiered Peritoneal Regression Grading Score (PRGS) has been proposed for assessment of histological treatment response. We aimed to evaluate the effect of immunohistochemistry (IHC) on interobserver agreement of the PRGS. Hematoxylin and eosin (H&E)-stained and IHC-stained slides (n = 662) from 331 peritoneal quadrant biopsies (QBs) taken prior to 99 PIPAC procedures performed on 33 patients were digitalized and uploaded to a web library. Eight raters (five consultants and three residents) assessed the PRGS, and Krippendorff's alpha coefficients (α) were calculated. Results (IHC-PRGS) were compared with data published in 2019, using H&E-stained slides only (H&E-PRGS). Overall, agreement for IHC-PRGS was substantial to almost perfect. Agreement (all raters) regarding single QBs after treatment was substantial for IHC-PRGS (α = 0.69, 95% confidence interval [CI] = 0.66-0.72) and moderate for H&E-PRGS (α = 0.60, 95% CI = 0.56-0.64). Agreement (all raters) regarding the mean PRGS per QB set after treatment was higher for IHC-PRGS (α = 0.78, 95% CI = 0.73-0.83) than for H&E-PRGS (α = 0.71, 95% CI = 0.64-0.78). Among residents, agreement was almost perfect for IHC-PRGS and substantial for H&E-PRGS. Agreement (all raters) regarding maximum PRGS per QB set after treatment was substantial for IHC-PRGS (α = 0.61, 95% CI = 0.54-0.68) and moderate for H&E-PRGS (α = 0.60, 95% CI = 0.53-0.66). Among residents, agreement was substantial for IHC-PRGS (α = 0.66, 95% CI = 0.57-0.75) and moderate for H&E-PRGS (α = 0.55, 95% CI = 0.45-0.64). Additional IHC seems to improve the interobserver agreement of PRGS, particularly between less experienced raters.

Communicating imaging findings in peritoneal mesothelioma: the impact of 'PAUSE' on surgical decision-making.

The peritoneal cavity is the second commonest site of mesothelioma after the pleural cavity. There are five histological types of peritoneal mesothelioma with variable symptomatology, clinical presentation and prognosis. Cystic mesothelioma is a borderline malignant neoplasm with a favourable prognosis, well-differentiated papillary mesothelioma is generally a low-grade malignancy, and all other varieties such as epithelioid, sarcomatoid and biphasic mesothelioma are highly malignant types of peritoneal mesothelioma with poor prognosis. Malignant peritoneal mesothelioma was considered inevitably fatal prior to the introduction of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) in selected cases where long-term survival and cure could be achieved. However, the survival benefits following CRS and HIPEC mainly depend on completeness of cytoreduction, which come at the cost of high morbidity and potential mortality. Using the acronym 'PAUSE', we aimed at describing the key imaging findings that impact surgical decision-making in patients with peritoneal mesothelioma. PAUSE stands for peritoneal cancer index, ascites and abdominal wall disease, unfavourable sites of involvement, small bowel and mesenteric disease and extraperitoneal disease. Reporting components of 'PAUSE' is crucial for patient selection. Despite limitations of CT in accurately depicting the volume of disease, describing findings in terms of PAUSE plays an important role in excluding patients who might not benefit from CRS and HIPEC.

Managing Recurrent Pseudomyxoma Peritonei in 430 Patients After Complete Cytoreduction and HIPEC: A Dilemma for Patients and Surgeons.

BACKGROUND: Epithelial appendiceal neoplasms are uncommon peritoneal malignancies causing a spectrum of disease including pseudomyxoma peritonei (PMP). The optimal management is cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). Despite complete CRS (CCRS), recurrence develops in almost 45% of patients. No consensus exists for the optimal treatment of recurrent disease, with treatment strategies including repeat CRS, watch-and-wait, and palliative chemotherapy. This report aims to describe evolving management strategies for a large cohort with recurrence after CCRS. METHODS: This retrospective study analyzed a prospective database of patients with recurrence after CCRS for appendiceal neoplasms from 1994 to 2017 who had long-term follow-up evaluation with tumor markers and computed tomography (CT). RESULTS: Overall, 430 (37.6%) of 1145 PMP patients experienced recurrence at a median of 19 months. Of these 430 patients 145 (33.7%) underwent repeat CRS, 119 (27.7%) had a watch-and-wait approach, and 119 (27.7%) had palliative chemotherapy. The patients with recurrence had a median overall survival (OS) of 39 months, a 3-year survival of 74.6%, a 5-year survival of 57.4%, and a 10-year survival of 36.5%. In the multivariate analysis, the patients who had recurrence within 1 year after primary CRS (hazard ratio [HR], 3.55), symptoms at recurrence (HR, 3.08), a high grade of disease or adenocarcinoma pathology (HR, 2.94), signet ring cells (HR, 1.91), extraperitoneal metastatic disease (HR, 1.71), or male gender (HR, 1.61) had worse OS. The OS was longer for the patients who had repeat CRS (HR, 0.41). The patients who underwent repeat CCRS had a 3-year OS of 87.5%, a 5-year OS of 78.1%, and a 10-year OS of 67.9%. CONCLUSIONS: Dilemmas persist around the optimal management of patients with recurrence after CRS and HIPEC for appendiceal tumors. Selected patients benefit from repeat CRS, particularly those with favorable tumor biology and focal disease.

New insights in the pathology of peritoneal surface malignancy.

Pathology is central to the management of peritoneal surface malignancy. This article highlights some recent advances that have had an impact on patient management or could do so in the near future. Malignant peritoneal mesothelioma, particularly the epithelioid subtype, is amenable to radical therapy in selected cases, and factors such as ki67 proliferation index, expression of BAP1 and mutation in CDKN2A show promise as prognostic indicators. Our understanding of multicystic mesothelioma has improved in recent years; it is a true neoplasm for which surgery may be indicated. Serous carcinomas involving the peritoneum are now known to originate from tubal epithelium. They are of two distinct types, high grade and low grade, which are now recognized as different neoplasms with distinctive features, oncogenesis and behavior. Pseudomyxoma peritonei (PMP) is an unusual condition that usually arises from an appendiceal mucinous neoplasm. Recent consensus in the classification and nomenclature of these lesions is discussed, including the distinction between low grade and high grade appendiceal mucinous neoplasms (HAMN), and the diagnostic criteria for appendiceal adenocarcinoma. PMP is divided into four prognostic groups: acellular mucin, low grade mucinous carcinoma peritonei, high grade mucinous carcinoma peritonei, and high grade mucinous carcinoma peritonei with signet ring cells. The pseudomyxoma microbiome is a promising area for clinical intervention but has been the subject of little research activity. Goblet cell adenocarcinoma (previously known as 'goblet cell carcinoid') is a distinctive type of appendiceal adenocarcinoma. Its behavior correlates with histologic features, but no general consensus for classification has been reached.

Patients undergoing cytoreductive surgery for peritoneal malignancy of appendiceal origin should be consented for umbilical excision as 30% have umbilical infiltration.

AIM: Cytoreductive surgery (CRS) for peritoneal malignancy has traditionally included umbilical excision with no published evidence on the incidence of umbilical involvement. The primary aim of this work was to determine the incidence of umbilical involvement in patients undergoing CRS for peritoneal malignancy of appendiceal origin. The secondary aim was to investigate the relationship of umbilical involvement with prior surgery affecting the umbilicus, such as diagnostic laparoscopy and midline laparotomy. METHOD: This study is from a national referral centre in the United Kingdom for appendiceal tumours and peritoneal malignancy. It is a retrospective analysis from a dedicated prospective database. We evaluated the most recent 200 consecutive patients who underwent CRS for peritoneal malignancy of appendiceal origin where all pathology specimens were reported by a recognized expert pathologist in appendiceal tumours and peritoneal malignancy. RESULTS: From June 2016 to September 2019, 200 consecutive patients had CRS and 178 had umbilical excision. Of these 54/178 (30.3%) had disease involving the umbilicus. The pathological findings in the 178 patients were low-grade mucinous carcinoma peritonei in 90/178 (50.6%), high-grade mucinous carcinoma peritonei in 31/178 (17.4%), metastatic appendiceal adenocarcinoma in 29/178 (16.4%) and diffuse acellular mucin in 28/178 (15.7%). Umbilical involvement was found in 25/90 (27.8%) with low-grade, 11/31 (35.5%) with high-grade, 8/29 (27.6%) with adenocarcinoma and 10/28 (35.7%) of patients with acellular mucin. In the 54 patients with umbilical disease, 30/54 (55.6%) had previous diagnostic surgery affecting the umbilicus. In the 124 patients without umbilical disease, 76/124 (61.2%) had prior surgery involving the umbilicus. The difference between the groups was not significant (p = 0.24). CONCLUSION: In patients with peritoneal malignancy of appendiceal origin, approximately 30% have umbilical involvement, irrespective of the primary appendiceal pathology. Umbilical involvement was not associated with prior surgery involving the umbilicus. This is the first report to document the incidence of umbilical pathology and supports consideration of routine umbilical excision in CRS for peritoneal malignancy.

Estimating the Prevalence of Pseudomyxoma Peritonei in Europe Using a Novel Statistical Method.

BACKGROUND: The determination of the incidence and prevalence of rare diseases is important for economists and health-care providers. Pseudomyxoma peritonei (PMP) is a rare, slow-growing abdominal cancer that represents a substantial burden on both patients and health-care systems. The incidence rate was previously approximated at 1-2 people per million per year; this incidence has never been challenged, and the prevalence has not been estimated. METHODS: Epidemiological data from Norway and England were obtained and analysed to calculate a minimum incidence rate based on the number of patients having a first surgical intervention for PMP. A novel method was then used to determine a prevalence rate for PMP, incorporating incidence, death, and cure rates in a multi-year analysis that accounted for the increasing population of Europe over a 10-year period. RESULTS: An incidence rate of 3.2 people per million per year was calculated, with a corresponding estimated prevalence rate of 22 people per million per year. By this calculation, 11,736 people in Europe were estimated to be living with PMP in 2018. CONCLUSION: Incidence and prevalence are essential tools for assessment of the financial and human cost of a disease. For rare diseases, such as PMP, the lack of accurate registries presents a particular challenge in determining such health-related statistical parameters. Based on our calculations, a significant number of people are living with PMP in Europe, underlining the need for appropriate resource allocation to ensure that adequate health-care measures are provided.

Updates in Appendix Pathology: The Precarious Cutting Edge.

Mucinous appendiceal tumors include low-grade appendiceal mucinous neoplasm, high-grade appendiceal mucinous neoplasm, and mucinous adenocarcinoma. Nonmucinous adenocarcinomas are less frequent. Recent consensus guidelines and the latest edition of the World Health Organization classification will allow consistent use of agreed nomenclature. Accurate diagnosis is important not only for patient management but also to allow comparison of results between centers and tumor registries. Serrated polyps are the most common benign polyp in the appendix. They need to be distinguished from low-grade appendiceal mucinous neoplasm, which can also mimic other benign conditions. Goblet cell adenocarcinomas are a distinctive type of appendiceal neoplasm.

Acellular mucin in pseudomyxoma peritonei of appendiceal origin: what is adequate sampling for histopathology?

INTRODUCTION: Acellular intra-abdominal mucin is associated with a favourable prognosis in pseudomyxoma peritonei. There are no current guidelines on how many blocks are needed to classify the mucin as acellular with confidence. METHODS: Specimens from cytoreductive surgery for mucinous appendiceal neoplasia, in which acellular mucin was found on initial histopathological examination, were prospectively identified. Additional tissue blocks were then taken to include either all residual visible intra-abdominal mucin or a maximum of 30 blocks. We also sent a questionnaire to pathologists in other centres. RESULTS: Twelve patients were identified. In two cases, neoplastic epithelial cells were found on taking additional blocks. The questionnaire results suggested considerable variation in block-taking practice. CONCLUSION: Taking additional tissue identified neoplastic cells in 2 of 12 cases. We recommend that sampling additional material should be considered when only acellular mucin is found on initial histology. Further work to determine the optimum sampling protocol is indicated.

Counting Intraepithelial Lymphocytes: A Comparison Between Routine Staining and CD3 Immunohistochemistry.

Counting intraepithelial lymphocytes (IELs) is a key part of the assessment of duodenal biopsies. Immunohistochemistry (IHC) for CD3 can aid identification of lymphocytes in this context, but it is not evident that counts on hematoxylin and eosin (H&E) and CD3 are comparable. This study aimed to compare the IEL counts in duodenal biopsies using H&E stains and CD3 IHC, and to examine the interobserver variability. Thirty-five paired H&E and CD3 sections were reviewed by 6 pathologists who counted the number of IELs per 100 enterocytes. The counts were categorized into groups: normal (<25 lymphocytes), mildly raised (25-40 lymphocytes), and markedly raised (>40 lymphocytes). CD3 IHC was associated with significantly higher IEL counts than H&E. Four cases with normal H&E counts had raised counts with CD3. There was moderate agreement between observers for both H&E and CD3. Lack of concordance between CD3 and H&E IEL counts suggests that counts derived from the 2 methods may not be comparable to each other and should not be considered equivalent. There was no significant improvement in interobserver variability with CD3 IHC.

Complicated appendiceal diverticulosis versus low-grade appendiceal mucinous neoplasms: a major diagnostic dilemma.

AIMS: To research and identify how often complicated diverticular disease of the appendix [appendiceal diverticular disease (ADD)] shows histological mimicry of low-grade appendiceal mucinous neoplasms (LAMNs) and to provide guidance on the useful histopathological features that allow the appropriate diagnosis to be made. METHODS AND RESULTS: Seventy-four cases of complicated appendiceal diverticular disease were identified from two specialist centres. Of the second opinion/consultation cases, 71% of the ADD cases had been diagnosed by referring pathologists as LAMNs. Salient pathological features were identified and agreed upon to reach the applicable diagnosis. For a diagnosis of complicated diverticulosis, particularly when associated with mucus cysts, the following morphological features were regarded as important: relative retention of the normal mucosal architecture with lamina propria and a maintained crypt architecture, crypts arranged in regular array, epithelial hyperplasia and a lack of nuclear abnormalities extending the length of the crypts. In a formal case-control study undertaken on 30 cases with each diagnosis, ADD and LAMN, loss of lamina propria, a filiform architecture and hypermucinosis were significantly associated with low-grade appendiceal mucinous neoplasms. Mucosal neuromas were significantly associated with diverticular disease of the appendix. CONCLUSIONS: To our knowledge, this study represents the largest series in the world literature and serves to highlight the important pathological features to distinguish complicated diverticular disease of the appendix from LAMNs, and emphasises the difficulties experienced by diagnostic pathologists in diagnosing complicated appendiceal diverticulosis. This is important, as LAMNs have a significant risk of transcoelomic spread, while complicated appendiceal diverticulosis has no such risk.

Diagnostic concordance in cases of appendiceal mucinous neoplasia referred to a tertiary referral centre.

Accurate diagnosis of appendiceal tumours and any associated peritoneal disease is clinically important but can be difficult. We retrieved the records of patients referred to the Peritoneal Malignancy Institute, Basingstoke, in the years 2016, 2017 and 2018 with a diagnosis of mucinous appendiceal neoplasia and identified 323 patients in which slides were reviewed as part of the referral pathway. Comparing the local report from the referring centre with the central review report, in 57 (18%) we identified a discrepancy. In 39 (12%) the discrepancy was in overall diagnosis, including 22 (7%) in which the local diagnosis was low-grade appendiceal mucinous neoplasm whereas the review diagnosis was reactive mucosal changes, usually due to ruptured diverticulum, with no evidence of neoplasia. Our findings support the practice of central review of histopathology slides by experienced pathologists at tertiary referral centres. They also suggest that improvements in diagnostic criteria are needed.