There is a need to refine the selection of patients with oropharynx squamous cell carcinoma (OPSCC) for treatment de-escalation. We investigated whether pre-treatment absolute lymphocyte count (ALC) predicted overall survival (OS) benefit from the addition of concurrent chemotherapy to radical radiotherapy.
PATIENTS 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). The primary endpoint was OS at 5 years. Locoregional control (LRC) was assessed using competing risk regression as a secondary endpoint. 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.
Pre-treatment ALC was prognostic for 5-year OS on multivariable analysis (hazard ratio [HR] 0.64, 95% confidence interval [CI] 0.42-0.98, p=0.04). It also predicted benefit from the use of concurrent cisplatin, with a significant interaction between cisplatin and pre-treatment ALC (likelihood ratio-test, p=0.04): higher ALC count reduced the 5-year OS benefit compared to radiotherapy alone (HR 2.53, 95% CI 1.03-6.19, p=0.043). This was likely driven by an effect on LRC up to 5 years (interaction sub-distribution HR 2.29, 95% CI 0.68-7.71, p=0.094). An independent validation cohort replicated the OS (HR 2.53, 95% CI 0.98-6.52, p=0.055) and LRC findings (interaction sub-distribution HR 3.43, 95% CI 1.23-9.52, p=0.018).
For OPSCC, the pre-treatment ALC is prognostic for OS and also predicts benefit from the addition of cisplatin to radiotherapy. These findings require prospective evaluation, and could inform the selection of good prognosis patients for a de-escalation trial.