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Is there a causal relationship between blood cultures after surgery for colorectal cancer and long‐term oncological outcomes?

We read with great interest the article by Watt et al.1. In this retrospective cohort study, Cox regression analyses showed that patients who had blood cultures taken within 30 days after colorectal cancer surgery had increased mortality and recurrence compared with patients who did not. Therefore, Watt et al. concluded that a clinically suspected infection requiring blood cultures within 30 days of surgery for colorectal cancer was associated with poorer oncological outcomes. However, we suggest the actual population at high risk of worse prognosis are those patients diagnosed with infectious complications (positive blood cultures), and not all patients who have blood cultures after surgery. These are really two different concepts. Here, we would like to use a similar analogy to aid understanding. Early studies found a significantly higher incidence of lung cancer in men than in women. Researchers initially suspected that gender difference in lung cancer incidence may be related to the effect of sex hormones. However, they soon realized that the real reason was that the rate of smoking was significantly higher in men than in women, and smoking is the main culprit for lung cancer. By the same token, in this study, complications of postoperative infection were probably the real culprit for the poorer prognosis, hidden behind the facade of requiring blood cultures. Numerous clinical studies have identified the causal relationship between postoperative infections and oncologic prognosis after colorectal cancer surgery2-4. Some possible mechanisms have also been found to explain this relationship, including the deregulated host immunological response during infection5.