New insights in the pathology of peritoneal surface malignancy

Abstract

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.

Keywords: Appendiceal neoplasms; mesothelioma; peritoneal neoplasms; pseudomyxoma peritonei (PMP); serous carcinoma.

Figure 1

Epithelioid malignant mesothelioma of peritoneum. There is a solid pattern on the left and a tubulopapillary pattern on the right. Hematoxylin and eosin, ×10.

Figure 2

Multicystic mesothelioma of peritoneum. This low power view demonstrates thin-walled cysts of varying size, typical of the neoplasm. Hematoxylin and eosin, ×2.

Figure 3

High grade serous carcinoma of the peritoneum. This high power view shows characteristically pleomorphic tumor cells. A mitosis is arrowed. Hematoxylin and eosin, ×40.

Figure 4

Low grade serous carcinoma of the peritoneum. There are papillae, nests and cribriform structures. Numerous psammoma bodies are present (arrow). Hematoxylin and eosin, ×10.

Figure 5

Low grade appendiceal mucinous neoplasm. The neoplastic epithelium shows an undulating pattern with scattered filiform villi. Cytologic atypia is minimal. The muscularis propria is indicated by a star. Hematoxylin and eosin, ×4.

Figure 6

Low grade appendiceal mucinous neoplasm showing pushing invasion. The neoplastic epithelium (arrow) makes a diverticulum-like structure pushing towards the serosal surface (arrowhead). Hematoxylin and eosin, ×2.

Figure 7

Mucinous adenocarcinoma of appendix, moderately differentiated. The ‘small cellular mucin pool’ pattern of invasion is visible. Clumps of tumor cells (arrow) surrounded by mucin invade the appendiceal wall. Hematoxylin and eosin, ×4.

Figure 8

Acellular mucin within the peritoneal cavity derived from a ruptured low grade appendiceal mucinous neoplasm. Hematoxylin and eosin, ×4.

Figure 9

Goblet cell adenocarcinoma. This lesion shows the typical nests of cells (group A in the Tang classification). Rare neuroendocrine cells with red granular cytoplasm are present (arrow). Hematoxylin and eosin, ×10.