Pseudomyxoma peritonei (PMP) is a clinical condition characterized by the accumulation of mucin within the peritoneal cavity, generally originating from appendiceal tumors [[1], [2], [3]]. The incidence of PMP is estimated to be one to three cases per million people per year [4]. Due to its rarity, there have been no randomized controlled trials for its treatment [1]. In the past, surgical debulking or repeated drainage of mucinous ascites was the only option for treating PMP [5,6]. Unlike other malignant tumors, PMP is localized to the peritoneal cavity for long periods and organ invasion is limited [[7], [8], [9]]. Therefore, aggressive local treatment is considered effective, and in recent years, a combination of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) has been considered as a standard treatment, with a 10-year overall survival rate of 50–60% [[10], [11], [12], [13], [14]].

In Japan, aggressive surgery as a cancer treatment is performed more frequently than in other countries [[15], [16], [17], [18], [19], [20]]. Examples include para-aortic nodal dissection and bursectomy for gastric cancer, extended lymphadenectomy for pancreatic cancer, and lateral pelvic node dissection for rectal cancer [[15], [16], [17], [18], [19], [20]]. In addition, there are aggressive surgeries for PMP at some medical centers in Japan [21]. There is a consensus that CRS combined with HIPEC improves the prognosis of patients with PMP; however, the optimal degree of invasiveness involving organ resection remains unknown. Specialized strategies must be formulated for PMP in general and for huge PMP in specific [22].

The peritoneal cancer index (PCI) is widely recognized as an indicator of the extent of peritoneal disease, including PMP [13,23]. However, in PMP patients, there is no cutoff value of the PCI to indicate whether complete cytoreduction is feasible [24]. Even with a maximum PCI score of 39, there are cases wherein complete cytoreduction is possible [25]. The PCI is a score that assesses the overall intra-abdominal disease burden and cannot represent the difficulty of surgery in an abdominal region. Tumors located in some regions are considered more difficult (or easier) to remove than those located in other regions; however, the difficulty by region has not been quantitatively evaluated.

Large-scale studies on PMP have only been reported in Europe [13,14,26], and it is worthwhile to conduct this study using data from Japan, where different treatment strategies are employed. This study aimed to assess the prognostic implications and survival outcomes of patients with PMP treated with curative-intent surgery and describe the patient characteristics and outcomes of the surgical procedure (e.g., total gastrectomy and total colectomy) included in CRS. In addition, this study aimed to verify differences in the difficulty of CRS by region in the abdominal cavity.