Abstract P2-07-04: Analysis of host inflammatory and estrogen biomarkers in JAKEE: A phase II trial of the JAK inhibitor ruxolitinib in combination with exemestane for estrogen receptor-positive metastatic breast cancer (2022)

Abstract Background: Circulating IL-6, an activator of JAK/STAT signaling, is associated with poor outcomes and aromatase inhibitor (AI) resistance in hormone-receptor positive (HR+) metastatic breast cancer (MBC). We previously presented clinical outcomes of JAKEE, a single arm, phase II, Simon two-stage clinical trial that tested Ruxolitinib (Rux), an oral selective inhibitor of JAK1/2, and exemestane (EXE) in 25 participants (pts) with HR+ MBC that relapsed/progressed on non-steroidal AI (NSAI); specifically, the primary endpoint of safety was met, but there were no complete or partial responses and 6/25 (24%) achieved stable disease (SD) for ≥6 cycles. We investigated whether host circulating inflammatory markers, IL-6 genotypes, and estrogen levels were associated with differential response to therapy.Methods: Responders (R) were defined as having achieved SD≥6 cycles. Flow cytometry was performed on baseline and on-treatment peripheral blood samples to assess downstream CD3+ T-cell phosphoSTAT3 inhibition by Rux. Serum concentrations of C-reactive protein (CRP), IL-6, serum amyloid A (SAA), Estrone (E1) and Estradiol (E2) were measured at baseline and serially on treatment. Sanger sequencing was performed to assess for three functional variants of the IL-6 promoter: −572G&amp;gt;C (rs1800796), −597G&amp;gt;A (rs1800797), and −174G&amp;gt;C (rs1800795), with high-risk polymorphisms being -597G/G and/or -174G/G. Non-parametric median testing was employed to test for differences in circulating markers by response groups given non-normal distribution, with a two-sided alpha of 0.05.Results: The cohort was heavily pre-treated: 28% received ≥2 lines of chemotherapy for MBC and 20% had CNS disease at enrollment. Among 17/25 pts with samples for pharmacodynamic assessment, Rux exhibited a 25% median inhibition (range 0-77%) of phosphoSTAT3. There was no differential effect in R vs non-responders (NR) (median inhibition 20% vs 29%, p=0.15). Frequency of high-risk IL-6 genotypes and distribution of baseline serum CRP, IL-6, SAA, E1 and E2 are depicted in the table. 15/25 (60%) harbored a high-risk IL-6 promoter polymorphism, with no significant difference in frequency between R and NR (50% vs 63%, p=0.65). 19 pts had samples for inflammatory biomarker analysis. 16/19 had baseline CRP≥10mg/L. While median levels of baseline CRP, SAA, and IL-6 were above upper limit of normal, there was no difference between R and NR (table). The proportion of pts with baseline undetectable E1 and E2 were similar between R and NR (E1: 36.9% vs 33.3%, p=1.0, E2: 52.6% vs 50%, p=1.0); notably, a significantly lower proportion with high-risk IL-6 genotype had undetectable baseline E1 (20% vs 60%, p=0.041), while no difference was noted for baseline E2, nor in the % change in E1 or E2 levels from baseline to cycle 4 by responder status.Conclusions: The JAKEE cohort represents an inflamed population with elevated circulating inflammatory markers and a high proportion with high-risk IL-6 genotypes. Examination of host inflammatory markers, IL-6 genotypes and estrogen levels did not reveal a differential response to the combination of Rux and EXE in patients with HR+ MBC that had progressed on prior NSAI. At tolerable dosing, Rux exhibited only a modest inhibition of phosphoSTAT3. Further work is needed to optimize strategies for targeting inflammation and JAK/STAT signaling in HR+ MBC. IL-6 GenotypeFrequencyFrequency by ResponderSignificanceHigh-Risk -174G/G and/or -597G/G15/25 (60%)Non-responder12/19 (63.2%)Responder3/6 (50%)p-value0.56Pretreatment Inflammatory Biomarkers [Upper limit of normal]Median (Range)Median Level by Responder GroupSignificanceCRP [8mg/L]SAA [10mg/L]IL-6 [2pg/mL]24.0 (0.2-146.8)12.8 (2.8-162.5)4.2 (1.8-11.5)Non-responder23.219.84.5Responder24.7 12.42.7p-value0.510.150.15Baseline Estrogen BiomarkersMedian (Range)Non-responderResponderp-valueEstrone (E1) (pg/mL)Estradiol (E2) (pg/mL)79.5.0 (0.2-1039.0)0.2 (0.2-44.1)79.8 0.247.8 4.20.410.91 Citation Format: Igor Makhlin, Nicholas McAndrew, E. Paul Wileyto, Amy Clark, Robin Holmes, Lisa N Bottalico, Grace R Jeschke, Kevin R Fox, Susan M Domcheck, Jennifer M Matro, Angela R Bradbury, Natalie Shih, Michael D Feldman, Elizabeth O Hexner, Jacqueline F Bromberg, Angela DeMichele. Analysis of host inflammatory and estrogen biomarkers in JAKEE: A phase II trial of the JAK inhibitor ruxolitinib in combination with exemestane for estrogen receptor-positive metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-07-04.