Ribonucleoside-diphosphate reductase subunit M2, also known as ribonucleotide reductase small subunit, is an enzyme that in humans is encoded by the RRM2 gene, inhibition of RRM2 can promote the apoptosis of NSCLC and head and neck squamous cell carcinoma (HNSCC) cell lines by increasing Bcl-2 degradation 33. Here, RRM2 is linked to head and neck squamous cell carcinoma.