The patients included in this study were confirmed as appendiceal pseudomyxoma peritonei by two experienced pathologists. In 2016, Peritoneal Surface Oncology Group International (PSOGI) divided PMP into four categories [12], as acellular mucin (AC), LG-MCP, HG-MCP, and HGMC-S. Their definition on PMP were regarded as a milestone [13]. All patients with AC had reached CCR 0–1, so our study analyzed the other three pathological types.

This paper mainly analyzed the effect of HIPEC in patients with appendiceal pseudomyxoma peritonei, and systematically clarified the factors affecting the prognosis and progression-free of PMP. PMP is a clinical syndrome characterized by the progressive accumulation of mucinous ascites within the peritoneal cavity [14]. The primary tumor is most commonly a perforated appendiceal mucinous tumor, but can also occur from other tumors such as ovarian, gastric, or colorectal cancers [15, 16]. The disease usually takes an indolent course with limited cases of lymph node or liver metastases reported [17,18,19]. According to the inclusion criteria, 526 patients were included in our study.

The median age of patients at hospitalization was 59 years (range 27–85), and the incidence rate of female was higher than that of male (57% vs. 43%). Most patients were diagnosed in local hospitals without receiving normative surgery. In these cases, the patients attended to our center for treatment only if they had enormous tumor burden. To some extent, this limits complete cytoreduction rather than operative skill. Other reports revealed that the small intestine was widely involved, the length of small intestine that be retained did not meet physiological and nutritional needs after operation, or the hilar structure was invaded, and the tumor cannot be completely removed [20,21,22,23]. PCI is a recognized index to evaluate tumor load worldwide. Extensive PMP is defined as the PCI ≥ 28 [21]. The median score of PCI in this paper was 31 points. Univariate analysis showed that PCI ≥ 31 can be used as a risk factor for poor prognosis in HGMC-S, and CCR 3 showed poor postoperative survival in LG-MCP compared with CCR 2. The results of a multicenter study on Peritoneal Surface Oncology Group International indicated that high peritoneal cancer index (P = 0.013) and debulking surgery (CCR, 2 or 3; P < 0.001) as independent predictors for a poorer progression-free survival [11]. Although PCI and CCR showed no survival difference in HG-MCP patients. Nevertheless, we recommend that a clear follow-up plan be developed after CRS and HIPEC to detect recurrence and plan following treatment.

In a present study, Narasimhan et al. reported a single-institution 10-year experience in management of appendiceal PMP with CRS and HIPEC. In their entire cohort, HIPEC was used in cases that had an incomplete cytoreduction. High-grade histology was a prognostic factor for a worse overall survival [23]. A previous study form Helsinki University Center Hospital reported 56(64%) patients received HIPEC (median PCI 20, range 5–29), 12(14%) were treated non-radically in an attempt at HIPEC (median PCI 34.5, range 29–39) [24]. However, the above two authors did not analyze the effect of HIPEC on prognosis. Glehen et al. analyzed the prognosis for 174 cases of PMP with non-radical resection. The results showed that HIPEC and repeated surgical resection were the factors to improve the survival of patients, and HGMC-S and lymph node metastasis were the significant risk factors affecting the prognosis [25]. A multicenter study evaluated the prognostic effect of HIPEC with CRS, compared with CRS alone, in patients with PMP. Their result demonstrated that the CRS-HIPEC group had better 5-year overall survival in CC-2/3 (16.1% [95% CI, 10.4–24.8%] vs. 28.4% [95% CI, 19.6–41.1%]; P = 0.007) [26]. High-grade histology was found to be independently associated with worse overall survival and progression-free survival. This is not unexpected, as other series also reporting histological grade influencing survival and progression-free survival [21, 22]. Other statistics revealed that male presented a worse prognosis in patients with LG-MCP and HG-MCP. These conclusions were consistent with the other two reports [27, 28].

In this study, we mainly focused on the role of HIPEC in different pathological types. In comparison of CRS and CRS + HIPEC in different pathology group, LG-MCP group had significant statistical differences in both postoperative survival and progression-free survival. It was indicated that HIPEC could prolong postoperative survival and progression-free survival of LG-MCP patients. Chua et al. also demonstrated that HIPEC was associated with an improved rate of progression-free survival [11]. However, there was no statistical differences in HG-MCP and HGMC-S group, which may be related to high degree of malignancy and poor prognosis. Our application of HIPEC in the treatment of HG-MCP and HGMC-S is mainly based on the control of malignant ascites, which is consistent with the reports of other scholars [21, 29]. In the present study, however, HIPEC with different drug regimens, PSC and previous surgery did not seem to be associated as much with the prognosis and progression-free survival. The same result of drug regimen in HIPEC has been elucidated in another study [11]. Likewise, the PMP response percentages to systemic chemotherapy were low [30]. In addition, previous surgery has also been proved no relevant to the prognosis and progression-free survival in PMP [6].