Does month of birth influence colorectal cancer prognosis?

PURPOSE: The main aim of this study was to identify a possible association between month of birth of colorectal cancer (CRC) patients and overall survival (OS) or disease-free survival (DFS). METHODS: This observational study included all consecutive adult patients diagnosed with CRC undergoing oncological surgery from January 2005 to December 2019 with a minimum follow-up of 10 years. The outcome variables were locoregional recurrence, death due to cancer progression, OS and DFS. Non-supervised learning techniques (K-means) were conducted to identify groups of months with similar oncologic outcomes. Finally, OS and DFS were analysed using Kaplan–Meier and Cox regression tests. The model was calibrated with resampling techniques and subsequently a cross-validation was performed. RESULTS: A total of 2520 patients were included. Three birth month groups with different oncologic outcomes were obtained. Survival analysis showed between-group differences in OS (p < 0.001) and DFS (p = 0.03). The multivariable Cox proportional hazards model identified the clusters obtained as independent prognostic factors for OS (p < 0.001) and DFS (p = 0.031). CONCLUSION: There is an association between month of birth and oncologic outcomes of CRC. Patients born in the months of January, February, June, July, October and December had better OS and DFS than those born in different months of the year. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00423-023-03161-3.