Macroscopic and microscopic characteristics of low grade appendiceal mucinous neoplasms (LAMN) on appendectomy specimens and correlations with pseudomyxoma peritonei development risk.

Low grade appendiceal mucinous neoplasm (LAMN) is the primary source of pseudomyxoma peritonei (PMP). PMP may develop after seemingly complete resection of primary tumor by appendectomy, which is unpredictable due to lack of reliable prognostic indicators. We retrospectively reviewed 154 surgically resected LAMNs to explore if any of the macroscopic and microscopic characteristics may be associated with increasing risk of PMP development. Our major findings include: (1) As compared to those without PMP, the cases that developed PMP were more frequent to have (a) smaller luminal diameter (<1 cm) and thicker wall, separate mucin aggregations, and microscopic perforation/rupture, all suggestive of luminal mucin leakage; (b) microscopic acellular mucin presenting on serosal surface and not being confined to mucosa; and (c) neoplastic epithelium dissecting outward beyond mucosa, however, with similar frequency of neoplastic cells being present in muscularis propria. (2) Involvement of neoplastic cells or/and acellular mucin at surgical margin did not necessarily lead to tumor recurrence or subsequent PMP, and clear margin did not absolutely prevent PMP development. (3) Coexisting diverticulum, resulted from neoplastic or non-neoplastic mucosa being herniated through muscle-lacking vascular hiatus of appendiceal wall, was seen in a quarter of LAMN cases, regardless of PMP. The diverticular portion of tumor involvement was often the weakest point where rupture occurred. In conclusion, proper evaluation of surgical specimens with search for mucin and neoplastic cells on serosa and for microscopic perforation, which are of prognostic significance, should be emphasized.

A Simplified Preoperative Assessment Predicts Complete Cytoreduction and Outcomes in Patients with Low-Grade Mucinous Adenocarcinoma of the Appendix.

BACKGROUND: Complete cytoreduction with hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) has been shown to improve survival in patients with low-grade mucinous adenocarcinoma (LGMA). However, incomplete cytoreduction exposes patients to significant morbidity without a similar survival benefit. Preoperative assessment of the ability to achieve CRS is therefore a critical step in selecting patients for CRS/HIPEC. OBJECTIVE: The aim of this study was to develop and validate a preoperative scoring system to accurately predict the ability to achieve complete cytoreduction in patients with LGMA of the appendix. METHODS: A simplified preoperative assessment for appendix tumor (SPAAT) score was developed based on computed tomography scan findings thought to predict incomplete cytoreduction. We applied the SPAAT score to patients with LGMA to determine the ability of the score to predict complete cytoreduction. This scoring system was then applied to a separate cohort of patients from a different institution. Sensitivity and specificity were determined for the SPAAT score. Survival was calculated and correlated with the SPAAT score and the completeness of cytoreduction score. RESULTS: A SPAAT score of <3 is a significant predictor of complete cytoreduction in the derivation cohort. In the validation cohort, 40 of 42 patients with a SPAAT score <3 achieved a complete cytoreduction, for a positive predictive value of 95.2 % and a negative predictive value of 100 %. Additionally, the SPAAT score was a significant predictor of disease-free survival. CONCLUSIONS: The SPAAT score is a useful tool in the preoperative assessment of patients with LGMA who are under consideration for cytoreductive surgery. Prospective analysis of this scoring system is warranted to appropriately select patients who will benefit from CRS/HIPEC.