Cancer patients exhibited significantly higher levels of complement C3 (1.26 ± 0.292 g/L) compared to co‐living individuals (1.26 vs. 1.12 g/L, p = 0.011), and complement C1q levels were also elevated in cancer patients (170.87 ± 29.319 mg/L) compared to co‐living individuals (170.87 vs. 158.89 mg/L, p = 0.032). Here, C3 is linked to cancer.