Abstract PO5-23-11: Elevated linoleic acid levels in red blood cells membrane predicts response to neoadjuvant chemotherapy in breast cancer patients

Abstract Introduction: Fatty acids (FA) consumed in the diet have been implicated in increasing the risk of breast cancer (BC). Humans have a wide variety of FAs, including saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) FAs. PUFAs can be further classified into omega-3 (n-3) and omega-6 (n-6) PUFAs. While n-3 has been associated with reducing inflammation and promoting apoptosis in BC cells, n-6 has been linked to increased inflammation, oxidative stress, and the promotion of BC cell proliferation and treatment resistance. In healthy women, the n-3 content in mammary tissue correlates with n-3 content in red blood cells (RBCs). The FA profile of the RBC membrane provides an unbiased option to assess lipid intake and composition, reflecting long-term FA intake and providing an objective and sensitive measure of lipid intake and body fat deposits. Notably, BC patients have been found to display a high n-6:n-3 ratio in RBCs, which is associated with inflammatory and oxidative stress biomarkers. The neoadjuvant chemotherapy treatment (NACT) model presents a unique opportunity to study resistance mechanisms in non-metastatic BC patients. In this approach, the absence of tumor (pathologic complete response: pCR, or Residual Cancer Burden (RCB) = 0) after NACT indicates treatment sensitivity and better overall survival (OS). Objective: The objective of this study is to determine whether differences in FA profiles determined in the RBC membrane and plasma are associated with the response to NACT in non-metastatic BC patients. Methods: A prospective study was conducted, including non-metastatic BC patients scheduled to receive NACT. Blood samples were collected before the first cycle of NACT to measure plasma and RBC FA derivatives, SFAs, MUFAs, and PUFAs. The pathological complete response (pCR) and residual cancer burden (RCB) were assessed. Results: A total of twenty-eight BC patients were included in the study. When comparing pCR vs. no-pCR using total SFA, MUFA, and PUFA plasma samples, no significant differences were observed. However, in RBC, an increase in PUFA was associated with a higher rate of no-pCR (**p< 0.01). Furthermore, comparing omega-6 and omega-3 (both PUFA) levels, an increase in omega-6 was associated with no-pCR (**p< 0.01), while no significant differences were observed with omega-3. No differences were obtained in plasma samples for either omega-6 and omega-3. To determine which specific omega-6 PUFAs were responsible for the association with no-pCR, elevated levels of linoleic acid (LA) in RBC were found to be associated with no-pCR (**p< 0.01). Other omega-6 PUFAs, including gamma-linolenic acid (GLA), eicosadienoic acid (EDA), dihomo-gamma linolenic acid (DGLA), and arachidonic acid (ARA), showed no significant associations. Multivariate and regression analysis confirmed LA (C18:2 n-6, LA) as the most relevant FA when assessing RCB (0-1 vs. 2-3) in RBC membranes, but not in plasma. The receiver operating characteristic (ROC) curve analyzing LA levels in RBC showed an area under the curve (AUC) of 0.855 for RCB (sensitivity: 76.9%, specificity: 92.3%). Conclusions: To the best of our knowledge, this is the first study demonstrating a clear connection between RBC membrane FA composition, specifically LA concentration, and the pathological response in BC patients after NACT. The measurements taken in plasma did not show significant associations, suggesting that RBC membrane FA profile of could serve as a relevant prognostic biomarker for studying resistance mechanisms to NACT in early BC patients Table. Measured FAs in RBC membrane and plasma by pathologic complete response *Indicates p<0.05; abbreviations: pCR: pathological complete response; SD: standard deviation; yr: years; BMI: body mass index; HR: hormone receptor; HER2: human epidermal growth factor receptor type-2; NLR: neutrophil to lymphocyte ratio; HG: histological grade; RCB: residual cancer burden; NA: not applicable Citation Format: Benjamin Walbaum, César Sánchez, Francisco Acevedo. Elevated linoleic acid levels in red blood cells membrane predicts response to neoadjuvant chemotherapy in breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-23-11.