Nearly two-thirds of
cancer patients are treated with
radiation therapy (RT), often with the intent to achieve complete and permanent
tumor regression (local control). RT is the primary treatment modality used to achieve local control for many
malignancies, including locally advanced
cervical cancer,
head and neck cancer, and
lung cancer. The addition of concurrent
platinum-based radiosensitizing
chemotherapy improves local control and patient survival. Enhanced outcomes with
concurrent chemoradiotherapy may result from increased direct killing of
tumor cells and effects on nontumor cell populations. Many patients treated with
concurrent chemoradiotherapy exhibit a decline in neutrophil count, but the effects of neutrophils on
radiation therapy are controversial. To investigate the clinical significance of neutrophils in the response to RT, we examined patient outcomes and circulating neutrophil counts in
cervical cancer patients treated with definitive chemoradiation. Although pretreatment neutrophil count did not correlate with outcome, lower absolute neutrophil count after starting
concurrent chemoradiotherapy was associated with higher rates of local control,
metastasis-free survival, and overall survival. To define the role of neutrophils in
tumor response to RT, we used genetic and pharmacological approaches to deplete neutrophils in an autochthonous mouse model of
soft tissue sarcoma. Neutrophil depletion prior to image-guided focal irradiation improved
tumor response to RT. Our results indicate that neutrophils promote resistance to
radiation therapy. The efficacy of
chemoradiotherapy may depend on the impact of treatment on peripheral neutrophil count, which has the potential to serve as an inexpensive and widely available
biomarker.