Association between serum baseline C1q and IgG levels and the efficacy of combined immunotherapy in patients with esophageal squamous cell carcinoma: a retrospective study

Background To assess the clinical value of serum complement component 1q (C1q) and immunoglobulin G (IgG) levels in predicting the response to combined immunotherapy in patients with esophageal squamous cell carcinoma. Methods We conducted a retrospective study of 44 patients with esophageal squamous cell carcinoma who received combined immunotherapy in our hospital. Serum IgG and C1q levels were collected before and three weeks after immunotherapy treatment, together with other data on clinical and demographic characteristics. Results Twenty seven patients (61.4%) showed partial response (PR), 13 (29.5%) stable disease (SD), and 4 (9.1%) progressive disease (PD). None of the patients presented complete response (CR). The PR group displayed lower IgG and higher C1q levels both before and after immunotherapy than patients showing SD or PD. The IgG reduction (59.3%) and C1q increment (70.3%) in the PR group three weeks post-treatment were significantly larger than those in patients showing SD or PD. Moreover, the pretreatment C1q level and the post-treatment change of C1q levels were strongly associated with the immunotherapy response. Conclusions High pre- and post-treatment C1q levels and reduced post-treatment IgG levels correlate with efficacy of combined immunotherapy in patients with esophageal squamous cell carcinoma. Serum baseline C1q level may predict immunotherapy response in such patients.