Pathology and prognosis in pseudomyxoma peritonei: a review of 274 cases.

AIMS: The classification of abdominal mucinous neoplasia is a controversial area. In 2010, WHO published a classification which divides pseudomyxoma peritonei (PMP) into low and high grades. The aim of the authors was to correlate this classification with the prognosis and site of primary neoplasm.
METHODS: The authors reviewed 274 patients with PMP who had undergone surgery at a single institution and classified them according to WHO criteria. The findings were correlated with clinical information and survival data.
RESULTS: PMP was low grade in 78% of patients and high grade in 22%. The appendix accounted for 94% of lesions, and the most common primary tumour was a low grade appendiceal mucinous neoplasm. Colorectal primaries were more likely to be associated with high grade PMP. There was an excellent correlation between the grade of the PMP and the primary neoplasm; only two cases showed discordant morphology: both were high grade appendiceal adenocarcinomas that were associated with low grade PMP. Nodal metastases were more likely in high grade lesions, but there was no significant difference in the rate of parenchymal organ invasion between low grade and high grade. Low grade morphology was associated with significantly longer survival than high grade (overall 5-year survival of 63% for low grade and 23% for high grade).
CONCLUSIONS: Categorisation as either low grade or high grade by WHO criteria correlates with prognosis. The grade of the PMP is generally consistent with the grade of the primary neoplasm. Colorectal primaries are more likely to be associated with high grade PMP.