Association of HO-1 expression with the effect of radiotherapy in nasopharyngeal carcinoma patients. A) shows the results between HO-1 negative group (N) and positive group (H + M). The comparison data among each treatment group (H, M and N) is showed in B). Data are described as Mean ± SE. *, P < 0.05; **, P < 0.0005. See text for details.