Abstract PO-066: Complete pathological response following neoadjuvant chemotherapy and recurrence free survival in patients with p16-positive oropharyngeal cancer

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Abstract Introduction: Locoregionally advanced p16+ squamous cell carcinoma of the oropharynx (OPSCC) is most often treated either with primary chemoradiation (CRT) or surgery followed by adjuvant treatment. Surgery alone is often insufficient treatment as adverse features such as extranodal extension, close or positive margins, lymphovascular invasion, or multiple positive lymph nodes are often identified, resulting in the need for adjuvant radiation or CRT. Primary surgery is often not pursued in more advanced cases since surgical pathology may show adverse features requiring adjuvant CRT, resulting in "triple therapy", the effects of which may worsen risk of long-term treatment toxicity. Our institution has demonstrated excellent oncologic and quality of life outcomes using a neoadjuvant chemotherapy (NAC) regimen of cisplatin and docetaxel prior to surgical treatment with TORS and neck dissection. Due to high rates of clinical-to-pathologic downstaging, adjuvant treatment is often avoided entirely. Here, we explore whether the development of a complete pathologic (pCR) response following NAC associates with 2-year recurrence free survival. Methods: A retrospective cohort study of patients receiving neoadjuvant doublet cisplatin and docetaxel followed by surgery (NAC+S) at a single institution between October 2015 and March 2023 was performed and pathologic responses and 2-year recurrence free survival was recorded following IRB exemption. Results: Fifty-four patients with p16+ OPSCC treated with NAC+S were identified. 49 patients (91%) received three cycles of NAC; 5 patients (9%) received two cycles. Comparing clinical staging to pathologic analysis of surgical specimens, 40 of 54 patients (68%) experienced clinical-to-pathologic downstaging after NAC. A pCR was identified in 23 of 54 patients (43%). Of patients that did not develop a pCR, 9 of 31 patients (29%) received adjuvant treatment due to the identification of high-risk pathologic features. Of patients that developed a pCR, 1 of 23 (4%) developed disease relapse within 2 years. Of patients that did not develop a pCR but did not require adjuvant treatment, 2 of 22 (9%) developed disease relapse within 2 years. Of patients that did not develop a pCR but did require adjuvant treatment, 2 of 9 (22%) developed disease relapse within 2 years. A trend toward reduced risk of disease relapse was observed in patients that develop a pCR following NAC compared to those that do not but did not reach statistical significance (1 of 23 relapses with pCR, 4 of 31 relapses without pCR; P>0.05, two-sided Chi-square test). Conclusion: High rates of pCR following NAC were observed in this small retrospective cohort of patients with newly diagnosed p16+ OPSCC despite 84% of patients avoiding any adjuvant treatment. Patients that develop a pCR after NAC trend toward reduced risk of recurrence compared to those that do not. The development of pCR after NAC may be a suitable short-term clinical outcome measure in prospective clinical trials of NAC for patients with newly diagnosed p16+ OPSCC. Citation Format: Alisha R. Pershad, Maxwell Madani, Timothy B. Shaver, Arjun Joshi, Clint T. Allen, Joseph F. Goodman. Complete pathological response following neoadjuvant chemotherapy and recurrence free survival in patients with p16-positive oropharyngeal cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-066.