Correlation between ribociclib resistance and circulating cytokines levels in metastatic breast cancer patients.
Authors: Garrone Ornella , Paccagnella Matteo , Abbona Andrea , Ruatta Fiorella , Denaro Nerina , Vanella Paola , Tomasello Gianluca , Gambini Donatella , Aprile Giuseppe , Di Maio Massimo , Merlano Marco Carlo 
Published: June 2022

e13037 Background: CDK4/6i, are the treatment of choice of hormone receptor positive metastatic breast cancer (mBC) patients (pts). Despite the improvements of survival achieved with CDK4/6i, resistance is challenging. The identification of biomarkers linked with the development of resistance is a need. Our aim was to identify whether circulating cytokines (cy) in mBC pts treated with ribociclib (R) plus endocrine therapy (ET) as first line treatment were predictive of resistance. Methods: Blood samples from mBC pts treated with R+ET were collected at baseline (T0) and at the time of the first evaluation (after 3 mos) (T1). Pts were subdivided on the basis of response. Group A: pts with objective response or stable disease at T1, Group B: pts who stopped treatment (ST) for any causes at T1. We evaluated the immune profile of 17 circulating cy: IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-13, IL-15, IL-21, TNF-α, TGF-β, IFN-γ, VEGF, CCL-2, CCL-4, CCL-22, CXCL-10 at each time points using Simple Plexsystem (ProteinSimple). IL-21 was evaluated through ELISA kit (R&D System). The differences in the median cy values were analyzed using non parametric Mann Whitney U test. HCPC analysis was performed to compare immunological profile of pts at T0 selecting only the normalized values of the best discriminating cy through ROC analysis between Group A and Group B. Clusters (C) generated through HCPC were compared for PFS and OS by Kaplan-Meyer analysis. Results: Up to now 32 out of 50 pts have been analysed. Among all cy only IL-8 plasma level at T0 in Group A (19 pts) was significantly lower compared to Group B (13 pts) (p = 0.025). ROC analysis selected all cy having a significance below 0.2 at T0. 8 cy were selected (IL-2, IL-4, IL-8, IL-10, IL-12, IL-15, IL-21 and CXCL-10) and were used as input variables to perform HCPC. HCPC identified 3 clusters. C1 contained only 1 pt., C2 11 pts and C3 20 pts. C2 was characterized by higher levels of IL-2, IL-8, IL-10, IL-12 and CXCL-10 compared to C3. Pts of group B were almost equally distributed in C2 (7 pts) and in C3 (6 pts). PFS of pts in C3 was significantly higher compared to pts in C2 (p = 0.006). All deaths (6) were comprised in C2. However at the moment no significant difference in OS has been observed. Conclusions: Despite only IL-8 was found significantly different between Group A and Group B, we were able to select 8 cy at T0 that may be important to identify patients who stop treatment at T1. HCPC identified 3 clusters. One of them included only 1 pt. C2 and C3 encompassed all ST pts (7 and 6 respectively). Albeit ST pts were similarly distributed in C2 and C3, pts in C2 showed a significantly lower PFS than pts in C3. It may be explained looking at the reason of treatment stop: disease progression (PD) in 7/7 pts in C2 and toxicity in 5/6 pts in C3. Therefore, C2 included 7 out of the 8 PD observed. Further studies on circulating cy will hopefully help to more precisely identify primary resistance to CDK4/6i.