Association of interleukin-8 and risk of incident and recurrent depression in long-term breast cancer survivors.

BACKGROUND:In cancer patients, an interleukin (IL)-8 gene variant that leads to higher production of IL-8, is associated with lower risk of depressive symptoms. In non-cancer adults, higher levels of IL-8 correlate with lower severity of depressive symptoms, decreased risk of suicide, and improved treatment response in females, but not males. This study evaluates the prospective association between circulating levels IL-8 and incident and recurrent major depressive disorder in breast cancer survivors. METHODS:In this single site, prospective cohort study with protocol modification extending follow-up from 24- to 32 months, recruitment occurred between September 2013 and January 2018, and follow-up was completed February 2021. Participants were identified from a Kaiser Permanente of Southern California health plan-based sample of 219 breast cancer survivors, who were two or more years since diagnosis of early stage breast cancer (TNM 0-II), aged 55 to 85 years, with no major depression or health events in last year. Circulating levels of IL-8 were obtained at enrollment. Primary outcome was time to incident or recurrent major depressive disorder as diagnosed by interview and DSM-5 criteria. RESULTS:Among 219 participants (mean age, 70 years; 100% female; 16 [7.3%] Asian, 42 [19.2%] Black, 161 [73.5%] White), 84% completed 24 months follow-up. After protocol modification, 59% completed 32 months follow-up. Median follow-up was 28.5 months. The primary endpoint occurred in 27 participants (12.4%, 5.7 events /100 person years; 95% CI 2.7 - 8.8). Higher IL-8 was associated with lower risk of incident and recurrent depression (hazard ratio, HR, 0.52, 95% CI 0.26 - 1.05). Among those with levels of IL-8 in the highest quartile, the primary endpoint occurred in 2 participants (3.6%; 1.6 events/100 person years; 95% CI 1.3 - 1.9), as compared to 25 participants in the pooled lower quartiles (15.2%; 7.2 events/100 persons years; 95%CI 7.0 - 7.4; rate difference, 5.6 per 100 person years, 95%CI 5.2 - 5.9; HR, 0.21, 95%CI 0.05 - 90, multivariable adjusted HR, 0.20, 95%CI 0.05 - 0.88). CONCLUSIONS:Among breast cancer survivors, higher IL-8 at enrollment was associated with a decreased risk of incident and recurrent major depression. These findings provide insights into mechanisms of depression risk and development of novel therapies for depression prevention, and suggest that testing for IL-8 may have prognostic value in identifying resilience or risk of depression.