To test for differences in the radio-responsiveness of the CD44+/ALDH + phenotype of HPV positive versus negative HNSCC cells, cell cultures were irradiated with a 4 Gy dose and analysed for changes in the proportion of this phenotype over intervals of 24, 48 and 72 hours, reflecting time intervals between fractionated doses in external radiotherapy. This evidence concerns the gene LDHA and head and neck squamous cell carcinoma.