Association Between Interleukin 6 Immunohistochemical and Plasma Levels in Invasive Ductal Carcinoma Breast: A Cross-Sectional Study

Background: Breast carcinoma (BC) is one of the most common malignancies in women, affecting 1 in 8.Interleukin 6 (IL6) isa proinflammatory cytokine. The role of IL6 pathways in breast cancer mo-tivated the development of anti-IL6 agents or monoclonal antibodies, which inhibit the IL6/signal transducer and activator of transcription 3 (STAT3) pathway. This study aimed to determine the proportion and intensity of immunohistochemical (IHC) IL6 expression in invasive ductal carcinoma (IDC) breast tissue sections and estimate plasma IL6 levels using an enzyme-linked immunosorbent assay (ELISA) in the same patients to evaluate the association between IHC and plasma IL6 levels. Methods: This laboratory observational cross-sectional study examined new primary BC cases be-tween January 2021 and June 2022. IL6 IHC was performed on tissue sections and analyzed using the histochemical (H)-score system. Plasma samples were taken from the same cases to estimate IL6 levels using an ELISA. The data were analyzed for an association between IHC and plasma IL6 levels in paired samples using SPSS software (version 22). Results: Among 50 IDC cases, the mean IHC-based IL6 H-score was 201.6 +/- 88.4, and the mean ELISA-based plasma IL6 level was 68.13 +/- 89.98 pg/mL. A slight positive correlation existed between IHC-based IL6 H-scores and ELISA-based plasma IL6 levels (p = 0.217). IHC-based IL6 H-scores were not associated with clinicopathological parameters. ELISA-based plasma IL6 levels were significantly associated with premenopausal status (p = 0.010), positive erb-b2 receptor tyrosine kinase 2 (ERBB2/HER2/NEU) expression (p = 0.040), low marker of proliferation Ki-67 (MKI67) index (p = 0.040), and the ERBB2/HER2/NEU enriched molec-ular category (p = 0.040). Conclusion: IHC-based IL6 H-scores increased with ELISA-based plasma IL6 levels among the cases. ELISA-based plasma IL6 levels were significantly associated with pre-menopausal status, positive ERBB2/HER2/NEU expression, low Ki-67 proliferative index, and the ERBB2/HER2/NEU enriched molecular category. Therefore, plasma IL6 could be a potential marker to assess prognosis in patients with IDC.