Hypoxia inducible factor (HIF1 alpha and HIF2 alpha) and carbonic anhydrase 9 (CA9) expression and response of head-neck cancer to hypofractionated and accelerated radiotherapy

Purpose: Tumor hypoxia and low intrinsic radiosensitivity may counteract the efficacy of standard radiotherapy for locally advanced head and neck cancer (HNC). We investigated the involvement of hypoxia-regulated proteins (Hypoxia inducible factors HIF1 alpha, HIF2 alpha and carbonic anhydrase CA9) in HNC resistance to accelerated and hypofractionated radiotherapy. Materials and methods: Thirty-nine patients with locally advanced HNC received 15 daily fractions of 3.4 Gy amounting to a total tumor dose of 51 Gy (equivalent to 63 Gy in four weeks - one week split); this was combined with platinum chemotherapy and amifostine cytoprotection administered subcutaneously. Immunohistochemical analysis of hypoxia-regulated proteins, namely HIF1 alpha, HIF2 alpha and CA9, was performed in formalin-fixed paraffin-embedded tissues obtained prior to radio-chemotherapy. Results: HIF1 alpha and HIF2 alpha were expressed in the nuclei and cytoplasm of cancer cells, while CA9 had a membrane reactivity. A high expression of HIF1 alpha, HIF2 alpha and CA9 was noted in 21/39 (53.8%), 20/39 (51.3%) and 23/39 (58.9%) cases, respectively. Complete response was obtained in 85.2% of patients and HIF1 alpha was marginally related with persistent disease after RT (p = 0.05). HIF1 alpha was significantly associated with poor local relapse free survival (LRFS) (p = 0.006) and overall survival (p = 0.008), whilst HIF2 alpha was not. A significant association of CA9 expression with poor LRFS was noted (p = 0.01). Conclusion: In accord with previously reported studies, high levels of the hypoxia regulated proteins HIF1 alpha and CA9 in HNC predict resistance to platinum based radio-chemotherapy. Whether HIF2 alpha expressing tumors are more sensitive to larger radiotherapy fractions, compared to standard radiotherapy fractionation, is an issue that deserves further investigation.