National statistics about resection of the primary tumor in asymptomatic patients with Stage IV colorectal cancer and unresectable metastases. Need for improvement in data collection. A systematic review with meta-analysis.

Background: Patients with asymptomatic Stage IV colorectal cancer represent a significant heterogeneous group. National statistics represent an effective method to follow in real time the clinical outcomes of patients, and they may represent an important tool to analyze and to compare different therapeutic approaches. The aim of our study was to analyze the reviews of national data and single institutions reports, which compared the clinical outcomes of patients with asymptomatic Stage IV colorectal cancer and un-resectable metastases who had resection of the primary tumor with those who did not have resection. We gave special attention to the number of missing established relevant variables, to determine the appropriateness of the results of the published studies.

Material: We performed a systematic review of papers comparing patients who had and who had not primary tumor resection. Screened reports included the time of publication from June 2012 to June 2018; 2556 papers were identified and 27 were included into the review. The primary outcome was observed survival. We analyzed the number of major missing variables in National Data Bases and Single Institution Reports, to assess the overall validity of the conclusions of the analyzed reports.

Results: In the majority of the reports and in the meta-analysis of studies with propensity score matching, resection of the primary tumor was correlated to improved survival and to the possibility for a better response to postoperative chemotherapy.

Conclusions: The high number of missing significant variables, and a clear clinical selection in single center reports make any analysis error-prone. National statistics might represent a valid method to follow in real time the clinical outcomes of these patients, comparing different therapeutic approaches. There is the need for improvement in national data collection, to make descriptive national statistics the ground for future progress in treatment. (PROSPERO) CRD 42018089691.