PIK3CA and head and neck squamous cell carcinoma: <h4>Background</h4>Tipifarnib, a farnesyl transferase inhibitor, has shown promising response in the treatment of HRAS-mutant HNSCC in the clinic, and in combination with a PI3K inhibitor in PIK3CA-mutant mouse models; however, the involvement of antitumor immunity in the efficacy of tipifarnib has not yet been investigated.