Positive GDNF stromal protein expression was associated with significantly worse PFS compared to negative expression in patients with HPV-negative HNSCC (HR 2.8, p = 0.021, S4B Table, Fig 5D); however, the difference did not reach statistical significance in HPV-positive HNSCC (HR 1.8, p = 0.197, S4A Table, Fig 5C). The gene discussed is GDNF; the disease is head and neck squamous cell carcinoma.