ICHNO-ECHNO 2022 - Abstract Book

S11

ICHNO-ECHNO 2022

Materials and Methods This was an observational study of consecutive OPSCCs treated by curative intent radiotherapy, with or without concurrent chemotherapy (n = 791) with external, independent validation from a separate institution (n = 609). Previously determined prognostic factors were used in a multivariable Cox proportional hazards analysis to assess the prognostic importance of ALC and the interaction between ALC and cisplatin use. Results Pre-treatment ALC was prognostic for overall survival (OS) on multivariable analysis (HR [hazard ratio] 0.64, 95% confidence interval [CI] 0.42-0.98, p = 0.04). There was a significant interaction between concurrent cisplatin use and pre-treatment ALC (likelihood ratio-test, p = 0.04): higher ALC count reduced the OS benefit compared to radiotherapy alone (HR 2.53, 95% CI 1.03-6.19, p = 0.043), a finding replicated in the external validation cohort (HR 2.53, 95% CI 09.98-6.52, p = 0.055) (Table, Figure).

Conclusion Pre-treatment ALC identifies patients with OPSCC who do not benefit from the addition of cisplatin chemotherapy to radical radiotherapy. This information should be used to select patients with good prognosis OPSCC for a de-escalation trial to investigate the omission of concurrent chemotherapy.