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Hot Topics in Appendiceal and Peritoneal Pathology

Carr, Norman John, FRCPath; Geisinger, Kim, MD

doi: 10.1097/PCR.0000000000000317
Editorial
Free

From the Basingstoke and North Hampshire Hospital.

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They are ill discoverers that think there is no land, when they can see nothing but sea.

Francis Bacon1

Readers seeing the title of this journal might have two questions: why devote an entire issue to what are mostly unusual conditions, and why combine the appendix and the peritoneum in one publication? The practical answer to the first question is that the neoplasms covered occur with sufficient frequency that any anatomic pathologist in general practice can expect to encounter them occasionally. Furthermore, they enter the differential diagnosis of more common conditions. The articles on goblet cell tumors of the appendix and low-grade mesothelial neoplasms exemplify these points.

Regarding the second question, a fascinating link between the appendix and the peritoneum is the syndrome known as pseudomyxoma peritonei. This singular disease arises from the appendix in the vast majority of cases. The tumor cells behave in a unique fashion, surviving within the abdominal cavity and spreading through it by following the flow of peritoneal fluid, but failing to metastasise in the way that would be expected of a typical colorectal adenocarcinoma. There is the tantalizing prospect that if we could understand why pseudomyxoma behaves the way it does, it might shed light on tumor growth and metastasis more generally, perhaps pointing the way to future avenues of research in other cancers.

There are many review articles on pseudomyxoma peritonei in the literature, and we hope that the one we present here is a bit different. We use a historical perspective to inform a discussion about the controversies of nomenclature and taxonomy that have plagued it for decades, leading to an account of a new consensus that aims to ensure we all speak the same language.2

Although pseudomyxoma peritonei is rare, mucinous appendiceal neoplasms are not. A common problem in differential diagnosis is the distinction between a low grade appendiceal mucinous neoplasm and its mimics, especially ruptured appendiceal diverticula. This is the focus of one of the articles. Regarding the genetics of appendiceal mucinous neoplasms, it is becoming clear that there are important differences in the genetic landscape between appendiceal lesions and similar-looking neoplasms of the colorectum, as discussed in another article in this issue. It seems inevitable that some of the answers to the unique behaviour of appendiceal neoplasms will be found in future genetic studies.

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REFERENCES

1. Bacon F. The Advancement of Learning, Second Book, edited by David Price. London: Cassell & Company; 1893.
2. Carr NJ, Cecil TD, Mohamed F, et al. A consensus for classification and pathologic reporting of pseudomyxoma peritonei and associated appendiceal neoplasia: the results of the Peritoneal Surface Oncology Group International (PSOGI) modified Delphi process. Am J Surg Pathol 2016;40:14–26.
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