Hypoxia-induced radioresistance in squamous cell carcinoma of the anus treated with radiotherapy − a validating study

To verify if hypoxia estimated by a 15-gene hypoxia classifier was prognostic for loco-regional failure (LRF) in a large real-world squamous cell carcinoma of the anus (SCCA) cohort and herby validate a previous hypothesis-generating study. RNA was extracted from pre-treatment paraffin-embedded biopsies of 304 patients treated with curative radiotherapy between 1998 and 2018, and gene expression analysis of 15 hypoxia-related genes was performed by quantitative polymerase chain reaction. Samples were classified as more or less hypoxic based on the expression of all 15 genes. The primary endpoint was LRF, estimated by the Aalen-Johansen estimator with distant failure and death as competing risks. Successful gene expression analysis was performed in 293 (96 %) cases. Classification resulted in 170 (58 %) less hypoxic tumors and 123 (42 %) more hypoxic tumors. High-risk features (high tumor stage and lymph node involvement) were more frequent in patients with more hypoxic tumors compared to less hypoxic tumors. Hypoxia was associated with increased LRFs with a cause-specific HR of 2.09 (95 % CI 1.32-3.30), p = 0.002. In multivariate Cox regression analysis, hypoxia remained prognostic for LRF (HR = 2.34 (95 % CI 1.35-4.06), p 0.002). The expression of the 15 hypoxia-related genes and classification of tumors as more or less hypoxic based on pre-treatment tumor tissue were prognostic for LRF in a large SCCA dataset. This underlines the importance of hypoxia in SCCA and validates the results from the previous hypothesis-generating study.