Background: Chemo decreases the risk of relapse and mortality from BC. Chemo efficacy depends on RDI, and patients (pts) who receive <85% RDI have poorer overall survival. Pro-inflammatory and coagulation factors such as IL-6, CRP and D-dimer serve as biomarkers for aging. The utility of these markers as biologic correlates of the ability to deliver chemo (i.e. RDI) in pts with BC is unknown. This study was performed to determine if prechemo IL-6, CRP and D-dimer correlate with RDI in women with stage I-III BC requiring chemo. Methods: This is a prospective longitudinal study that enrolled 153 women with BC who had pre-chemo peripheral blood assayed for IL-6, CRP, and D-dimer. (Neo)Adjuvant chemo regimens were prescribed at the physician’s discretion. Univariate analyses evaluated the association of these 3 markers with <85% RDI and clinical factors (patient age, physician rated Karnofsky performance status (KPS) and number of co-morbidities). Multivariate analyses were performed to evaluate the association of each biomarker and clinical factor with RDI. Results: 153 pts (mean age of 56 y, range 30-81 y) with stage I-III BC (Stages I [23%], II [54%], III [24%]) were enrolled. Chemo regimens include: doxorubicin+cyclophosphamide /paclitaxel (AC-T: 44%), docetaxel+cyclophosphamide (TC: 35%), docetaxel/carboplatin/trastuzumab (TCH: 7%) and other regimen (14%). RDI was less than 85% for 26% of pts. There were associations between RDI <85% and higher D-dimer (p<0.01) and IL-6 (p=0.02) levels pre-chemo (Table 1). There was no association between RDI <85% and CRP or above clinical factors. Conclusions: Higher pre-chemo levels of IL-6 and D-dimer correlate with reduced RDI (<85%). Future studies are underway to validate these findings. Table 1. Association of pre-chemo biomarkers, clinical factors and RDI <85%. Clinical trial information: NCT01030250