To date, few studies have looked at the role of tumor microenvironment in radiosensitization by PARP inhibition, although effects on the vasculature, such as decreases in tumor vascular density (13) or tumor vascular perfusion (11), have been implicated in potentiation of radiation therapy by PARP inhibition in lung cancer xenografts. The gene discussed is PARP1; the disease is lung carcinoma.