Analysis and results of Ku and XRCC4 expression in hypopharyngeal cancer tissues treated with chemoradiotherapy

Abstract

DNA double-strand break (DSB) is one of the most serious forms of damage induced by ionizing irradiation. Non-homologous end-joining (NHEJ) is a key mechanism of DNA DSB repair. The immunohistochemical analysis of proteins involved in NHEJ may have potential as a predictive assay for tumor radiosensitivity. We examined the correlation between the expression of proteins involved in DNA DSB in biopsy specimens and the results of chemoradiotherapy in hypopharyngeal cancers. Fifty-seven patients with previously untreated squamous cell carcinoma of the hypopharynx were treated between March 2002 and December 2009. Most patients (75%) had stage III or IV disease. The chemotherapy consisted of cisplatin plus 5FU or S-1. A tumor dose of 50 Gy was usually administered to the primary tumor and regional lymph nodes. Doses of 10-20 Gy were usually added to the primary tumor with reduced fields after 50 Gy. The 5-year disease-free survival rate was 100% for patients in stage I, 90% in stage II, 64% in stage III and 50% in stage IV. In stages I-III, patients with a lower expression of Ku70 or XRCC4 tended to have better locoregional control. These results indicated that a lower expression of Ku70 or XRCC4 may be correlated with higher radiosensitivity. Two patients had distant metastasis alone, of which one had 0% expression of Ku70 and the other had 0% expression of Ku86. The absence of Ku70 or Ku86 expression indicates low DNA-PK activity. Low DNA-PK activity due to a low expression of Ku may result in the genetic alteration of cancer cells, leading to a higher tendency of distant metastasis. This finding suggests that proteins involved in NHEJ may have an impact on the treatment results of chemoradiotherapy in hypopharyngeal cancer.