Aims A wide spectrum of well‐differentiated neuroendocrine proliferations (NEPs) are observed in inflammatory bowel disease (IBD), ranging from neuroendocrine tumours (NETs) to microscopic neuroendocrine cell clusters, best described as neuroendocrine cell micronests (NCMs). Finding NCMs in surveillance biopsies of IBD patients often poses a diagnostic conundrum. While such lesions may have been referred to as ‘microcarcinoids’ in the literature, it is unclear whether these represent early neoplasms. The study was undertaken to characterise NCMs and to differentiate NCMs from NETs. Methods and results Institutional surgical pathology archives were searched to identify cases of NEPs in IBD patients. Clinicopathological features were examined. NCMs were defined as scattered, indistinct neuroendocrine cell clusters without confluent growth or new stroma formation, located in the lamina propria and muscularis mucosae. NETs were defined as discrete, mass‐forming lesions. Seventeen NEPs were identified, including eight NCMs and nine NETs. All NEPs were incidentally discovered. While NETs were commonly found in the rectum and appendix, NCMs were only noted in the rectosigmoid area. Unlike NETs, NCMs could not be measured as a discrete lesion as these clusters were non‐confluent and scattered. None of the patients with NCMs developed NETs after a mean follow‐up of 4.1 years (range = 0.5–21.0 years). None of the NETs showed NCMs in the background mucosa. Conclusions NCMs have distinct pathological features, are not associated with NETs in IBD patients and should not be misinterpreted as ‘microcarcinoids’. Identification of NCMs in surveillance biopsies may not require further clinical work‐up or invasive procedures usually performed for NETs.

While researchers know that tumor mutational burden (TMB) is low in hepatocellular carcinoma (HCC), prior studies have not investigated TMB in cirrhosis, small early HCC and progressed HCC. HCC (n = 18) and cirrhosis (n = 6) cases were identified. TMB was determined by a 1.7 megabase, 409-gene next-generation sequencing panel. TMB values were defined as the number of nonsynonymous variants per megabase of sequence. There was no significant difference between cirrhosis versus small early HCC or between cohorts when stratified by size, early versus progressed, differentiation or morphology. There was a significant difference between cirrhosis and small early HCC versus progressed HCC (p = 0.045), suggesting TMB may be related to HCC progression. TMB similarities in small early HCC and background cirrhosis suggest TMB is not a useful tool for diagnosing small early HCC. Additional study is needed to address TMB in histological and molecular subsets of HCC.

Aims Gastric dysplasia is a risk factor for synchronous and subsequent gastric carcinoma. Distinguishing gastric dysplasia from reactive changes is subject to interobserver disagreement and is a frequent reason for expert consultation. We previously used assessment of surface cell polarity (the ‘four lines’) as a key feature to decrease equivocal diagnoses in Barrett oesophagus. In the current study, we examined for the presence or absence of the four lines in gastric dysplasia and reactive gastropathy. Materials and methods The study includes all (n = 91) in‐house biopsies with at least gastric dysplasia from the surgical pathology archives of two academic institutions during a 5‐year period from 2008 to 2012. A reactive gastropathy group (n = 60) was created for comparison. Results The dysplasia/neoplasia group was comprised of 14 biopsies of gastric foveolar‐type dysplasia, 59 of intestinal‐type dysplasia, 14 with dysplasia in fundic gland polyps, three pyloric gland adenomas and one oxyntic gland adenoma. Loss of surface cell polarity was seen in all 88 dysplasia cases with evaluable surface epithelium. All 57 reactive gastropathy cases with evaluable surface epithelium showed intact surface cell polarity except in focal areas directly adjacent to erosions in 17 cases, where the thin wisp of residual surface mucin could not be appreciated on haematoxylin and eosin. Conclusion Surface cell polarity (the four lines) was lost in all gastric dysplasia biopsies with evaluable surface epithelium and maintained in all biopsies of reactive gastropathy. Caution should be taken in using this feature adjacent to erosions in reactive gastropathy.

Background. In this single-institution study, we applied the current (eighth edition) American Joint Committee on Cancer pathologic staging criteria to 64 low-grade mucinous neoplasms of the appendix (LAMNs), examined their histopathologic features, and studied the patients’ clinical outcomes. Design. Sixty-four LAMNs, with a median follow-up of 52 months, were reviewed. Results. The distribution of pathologic stages was pTis (n = 39), pT3 (n = 1), pT4a (n = 5), pT4aM1a (n = 8), and pT4aM1b (n = 11). Recurrence was observed in only 2 patients (both with pT4aM1b disease), one of whom died of disease. All remaining patients were disease-free after a median clinical follow-up of 60 months. Conclusions. Our study confirms that pTis LAMNs have an excellent prognosis and suggests that pT4a and pT4aM1a LAMNs may also have a low risk of developing progressive disease.

Aims Recent studies from multiple global regions have reported a resurgence of lymphogranuloma venereum (LGV) proctitis, which is caused by Chlamydia trachomatis (CT). LGV proctitis is histologically indistinguishable from other forms of sexually transmitted proctitis and is difficult to differentiate from inflammatory bowel disease. While immunohistochemical stains are available for syphilis, there is no commonly available stain for the tissue identification of CT. Materials and methods From 200 positive CT nucleic acid tests (NAT) from anorectal swabs, we identified 12 patients with biopsies collected from the distal colorectum or anus within 90 days of the positive NAT. We collected basic demographic information and tabulated clinical and histological findings. We examined the performance of a novel RNA in‐situ hybridisation (ISH) stain targeting CT 23s rRNA on these 12 cases and 10 controls from the anorectum. Results All 12 patients were male; nine were HIV+, two had concurrent gonococcal infection, one had concurrent syphilis and one had cytomegalovirus co‐infection. The majority of biopsies (11 of 12) showed mild or moderate acute inflammation, had a prominent lymphoplasmacytic infiltrate (eight of 11) and lacked marked crypt distortion (10 of 10). The RNA ISH stain was positive in 10 of 12 cases (sensitivity 83%). One case showed equivocal staining. No controls showed definitive positive staining (specificity 100%). One had equivocal staining. Conclusion Our series showed that anorectal LGV had similar histological findings to those of prior STI proctitis series predominantly comprised of syphilis. The novel RNA ISH stain was sensitive and specific and may show utility in differentiating types of STI proctitis.