Pathogenesis of histologic variations of appendiceal mucinous neoplasms

Background In order for peritoneal metastases from a primary appendiceal mucinous neoplasm to occur, the wall of the appendix must perforate to allow mucus with tumor cells access to the peritoneal spaces. With progression the peritoneal metastases show a broad spectrum of tumor biology varying from indolent to aggressive activity. Methods The histopathology of peritoneal tumor masses was determined from the clinical material resected at the time of cytoreductive surgery (CRS). All groups of patients were treated by a uniform strategy that involved complete CRS and perioperative intraperitoneal chemotherapy. Overall survival was determined. Results From a database of 685 patients, four histologic subtypes were identified and long-term survival determined. Four hundred and fifty patients (66.0%) had low-grade appendiceal mucinous neoplasm (LAMN), 37 patients (5.4%) had mucinous appendiceal adenocarcinoma of intermediate subtype (MACA-Int), 159 patients (23.2%) had mucinous appendiceal adenocarcinoma (MACA), and 39 patients (5.4%) had a mucinous appendiceal adenocarcinoma with positive lymph nodes (MACA-LN). The mean survival of the four groups was 24.5, 14.8, 11.2 and 7.4 years, respectively (p < 0.0001). These four subtypes of mucinous appendiceal neoplasms were shown to have distinct survival estimates. Conclusions The estimated survival of these four histologic subtypes in patients having a complete CRS plus HIPEC is of value to the oncologist managing these patients. A mutations and perforations hypothesis was offered in an attempt to explain the broad spectrum of mucinous appendiceal neoplasms that exist. Inclusion of MACA-Int and MACA-LN as standalone subtypes was thought to be necessary.