Systemic cytokine dynamics during neoadjuvant chemotherapy versus endocrine therapy and CDK4/6 inhibition in high-risk luminal breast cancer: Results from the GEICAM/2019-01-CARABELA trial.

619 Background: Chemotherapy (CT) and CDK4/6 inhibitors modulate antitumor immunity primarily within the tumor microenvironment. Whether these effects are reflected systemically during neoadjuvant therapy, differ by treatment, or are associated with response remains unclear. Methods: CARABELA is a randomized neoadjuvant trial comparing letrozole (ET) + the CDK4/6 inhibitor abemaciclib vs standard CT in high-risk HR+/HER2− breast cancer. Plasma cytokines were measured at baseline (BL), 2 weeks (wks), 12 wks, and end of treatment (EOT) using multiplex proximity extension assay (Olink Target 96 Immuno-Oncology panel). Analyses included: (1) BL cytokine profiles by menopausal status, Oncotype DX Breast Recurrence Score test result (RS ≤25 vs >25), and Ki67 (<40% vs ≥40%); (2) longitudinal cytokine changes (BL to 2 and 12 wks, Δ) by residual cancer burden (RCB 0/I vs II/III), overall and by treatment; (3) EOT cytokine profiles by RCB. Group comparisons were adjusted by false discovery rate (FDR) threshold of 5% controlled by the q-value method. Multivariable logistic regression models were adjusted for menopausal status. Treatment–cytokine interactions were evaluated. Results: At BL, 40 cytokines were differentially expressed by menopausal status, with most showing higher levels in postmenopausal patients, including myeloid-associated inflammatory chemokines (CXCL9, CXCL10, MCP-1, MCP-4), angiogenic/matrix-remodeling factors (VEGFA, HGF, MMP7, MMP12), and TNF-related/immune regulatory molecules (TNFRSF12A, TNFRSF9, Galectin-9), indicating chronic systemic inflammation, without enrichment of cytotoxic immune effector programs. No BL cytokine differences met FDR threshold by RCB, RS or Ki67. Early cytokine changes (BL-2 wks) were not associated with RCB. In the ET + abemaciclib arm, no significant changes were observed between BL and 12 wks. In the CT arm, 25 cytokines had a significant increase (BL-12 wks) in patients with RCB II/III with respect to patients with RCB 0/I. These included inflammatory chemokines (IL8, CXCL1, CXCL5, CCL3, CCL4, MCP-3, MCP-4), angiogenic/growth factors (VEGFA, ANGPT1, EGF, PDGF-B), and stress-/TNF-related signaling molecules (CASP-8, TNFSF14, ADA). These cytokines were associated with RCB II/III in multivariable models adjusted for menopausal status. Cytokine–treatment interaction tests did not meet FDR threshold. Conclusions: Postmenopausal women display a distinct cytokine profile consistent with chronic systemic inflammation. Neoadjuvant CT induces pronounced systemic cytokine changes, while ET + CDK4/6 inhibition does not. Increased inflammatory and angiogenic cytokines during CT are associated with residual disease, supporting longitudinal systemic immune profiling as a marker of treatment resistance in high-risk luminal breast cancer. Clinical trial information: NCT04293393 .