Metachronous peritoneal carcinomatosis after pT4 colon cancer patients
pT4 colon cancer has been proposed as an important risk factor for metachonous peritoneal carcinomatosis and, therefor, second look +/- HIPEC had been advocated in this context. Although controversy still exist, even more after the results of two randomized clinical trials designed to answer that question, epidemiologic data are quite inaccurate because they come from previous works with very heterogeneous methodology, mixing colon cancer and rectal cancer and data coming from old papers or, even being recent, papers that analyzed old cohorts. Taking all these considerations into account we designed a study that evaluated more accurately epidemiology of metachronous peritoneal carcinomatosis in those patients with pT4 colon cancer after curative resection. We designed an observational retrospective multicentre trial with participation of 50 different hospitals at a nationwide level. All consecutive patients operated on because of colon cancer with curative intent, both elective and emergency operations, with pathologic confirmation of pT4 stage adenocarcinoma, were included in the database, during a three year period time (2015-2017). Colon cancer was considered as tumours located in the large bowel 15 cm above de anal verge. The exclusion criteria were as follows: patients younger than 18 years, R2 cancer resection, inclusion in other randomized clinical trials, and pathologic diagnosis of colon cancer other than adenocarcinoma, such as GIST, leiomyosarcomas, neuroendocrine tumors, or other types even more unusual. Patients with missing information were also excluded from the data analysis. Outcome measures The main outcome of the study was the incidence of metachronous peritoneal metastasis after curative resection for confirmed pT4 colon cancer patients and peritoneal recurrence free survival (PRFS). Secondary outcomes were considered local and systemic recurrence incidence, mid- to long-term oncologic results in terms of disease-free survival (DFS) and overall survival (OS), analysis of associated factors with peritoneal recurrent disease and to create a stratification risk model for peritoneal recurrence based on this National Multicentre Cohort. Statistical Method Qualitative variables are presented with their frequency distribution. Quantitative variables are represented by their mean and standard deviation or median and interquartile range in case of asymmetry. Univariate analysis was performed to assess the association between the different independent variables with peritoneal disease-free survival. In order to correct for confounding factors, a multivariate analysis was performed using a Cox proportional hazard model. Variables that had a p<0.01 in the univariate analysis were included in the multivariate analysis. The selection of the definitive model was carried out using the forward stepwise method with an inclusion value in the model of p <0.05 and exclusion of p>0.10. p<0.05 was considered to indicate statistical significance.