This systematic review and meta-analysis aimed to quantify the association between cancer treatment delay and mortality, specifically focusing on each four-week increase in delay. The study included 34 studies covering 17 indications for seven major cancers (bladder, breast, colon, rectum, lung, cervix, and head and neck) and three treatment modalities (surgery, systemic treatment, and radiotherapy). The main outcome measure was the hazard ratio for overall survival for each four-week delay. The results showed a significant association between delay and increased mortality for 13 of the 17 indications. For surgery, a four-week delay was associated with a 6-8% increase in the risk of death. For systemic treatment and radiotherapy, the associations varied more widely, with hazard ratios ranging from 1.01 to 1.28. The study concluded that even a four-week delay in cancer treatment is associated with increased mortality across various cancer types and treatment modalities, highlighting the need for policies focused on minimizing system-level delays to improve population-level survival outcomes.This systematic review and meta-analysis aimed to quantify the association between cancer treatment delay and mortality, specifically focusing on each four-week increase in delay. The study included 34 studies covering 17 indications for seven major cancers (bladder, breast, colon, rectum, lung, cervix, and head and neck) and three treatment modalities (surgery, systemic treatment, and radiotherapy). The main outcome measure was the hazard ratio for overall survival for each four-week delay. The results showed a significant association between delay and increased mortality for 13 of the 17 indications. For surgery, a four-week delay was associated with a 6-8% increase in the risk of death. For systemic treatment and radiotherapy, the associations varied more widely, with hazard ratios ranging from 1.01 to 1.28. The study concluded that even a four-week delay in cancer treatment is associated with increased mortality across various cancer types and treatment modalities, highlighting the need for policies focused on minimizing system-level delays to improve population-level survival outcomes.