RESUMEN
<p><b>OBJECTIVE</b>To explore the mechanism of arsenic trioxide (ATO) in enhancing radiotherapy in nasopharyngeal carcinoma (NPC) patients.</p><p><b>METHODS</b>Seventy-four patients with NPC of T(1-4) N(0-1)M0 were randomized into two groups: 35 patients in Group A were treated with conventional radiotherapy alone, and the 39 in Group B received radiotherapy and additional administering of ATO. The regressions of nasopharyngeal lesions and cervical lymph nodes were compared between the two groups at 40 Gy of radiation was given. And biopsy of the tissue from NPC was taken before treatment and 24 h after radiation of 20 Gy to determine the-expressions of proliferating cell nuclear antigen (PCNA), Bcl-2, Bax and p53 protein by immunohistochemistry.</p><p><b>RESULTS</b>When irradiation for 40 Gy, the completely regression rates of nasopharyngeal lesion were 20.0% (7/35) in Group A and 43.6% (17/39) in Group B, showing significant difference between them (chi2 = 4.684, P = 0.003), but no significant difference was shown between the two groups in regression rate of cervical lymph node. Expression of PCNA, Bax, Bcl-2 and p53 protein was reduced in both groups, but significant difference only showed between pre- and post-treatment in PCNA (Z = -2.449, P = 0.014) and Bax protein (Z = -3.031, P = 0.002) in Group B. Significantly reduction of PCNA (Z = -2.656, P = 0.008), Bax (Z = -2.359, P = 0.018) and p53 protein (Z = -1.999, P = 0.046) in patients with complete tumor regression at radiation for 20 Gy, while in those with no complete tumor regression only PCNA showed significant reduction (Z = -32.815, P = 0.015).</p><p><b>CONCLUSION</b>ATO shows effect in enhancing radiotherapy on NPC patients, its mechanism might be associated with the down-regulation of PCNA and apoptosis related protein and the inhibition on tumor proliferation and apoptosis inducing.</p>