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BACKGROUND: Chemotherapy efficacy is largely dependent on treatment adherence, defined by the relative dose intensity (RDI). Identification of new modifiable risk factors associated with low RDI might improve chemotherapy delivery. Here, we evaluated the association between low RDI and pre-chemotherapy factors, including patient- and treatment-related characteristics and markers of inflammation.

METHODS: This exploratory analysis assessed data from 267 patients with early-stage breast cancer scheduled to undergo (neo-)adjuvant chemotherapy included in the Physical training and Cancer (Phys-Can) trial. The association between low RDI, defined as < 85%, patient-related (age, body mass index, co-morbid condition, body surface area) and treatment-related factors (cancer stage, receptor status, chemotherapy duration, chemotherapy dose, granulocyte colony-stimulating factor) was investigated. Analyses further included the association between RDI and pre-chemotherapy levels of interleukin (IL)-6, IL-8, IL-10, C-reactive protein (CRP) and Tumor Necrosis Factor-alpha (TNF-α) in 172 patients with available blood samples.

RESULTS: An RDI of < 85% occurred in 31 patients (12%). Univariable analysis revealed a significant association with a chemotherapy duration above 20 weeks (p < 0.001), chemotherapy dose (p = 0.006), pre-chemotherapy IL-8 (OR 1.61; 95% CI (1.01; 2.58); p = 0.040) and TNF-α (OR 2.2 (1.17; 4.53); p = 0.019). In multivariable analyses, inflammatory cytokines were significant association with low RDI for IL-8 (OR: 1.65 [0.99; 2.69]; p = 0.044) and TNF-α (OR 2.95 [1.41; 7.19]; p = 0.007).

CONCLUSIONS: This exploratory analysis highlights the association of pre-chemotherapy IL-8 and TNF-α with low RDI of chemotherapy for breast cancer. IL-8 and TNF-α may therefore potentially help to identify patients at risk for experiencing dose reductions. Clinical trial number NCT02473003 (registration: June 16, 2015).