Quantifying smoking exposure, genomic correlates, and related risk of treatment failure in p16+ squamous cell carcinoma of the oropharynx

Abstract

Objectives: HPV-associated (p16+) squamous cell carcinoma of the oropharynx (OPSCC) has improved survival as compared to HPV-negative, smoking-associated disease. Intermediate outcomes have been noted in patients with p16+ tumors and smoking exposure. However, the extent of smoking exposure required for outcomes to decrease has not been delineated due to low failure rates and poor availability of quantitative tobacco smoke exposure data. Our primary objective is to characterize the dose-dependent relationship between recurrence-free survival (RFS) and tobacco smoke exposure in p16+ OPSCC and secondarily correlate tobacco smoke exposure with genomic alterations.

Methods: Single institution chart review was performed of patients diagnosed with p16+ OPSCC from 2003 to 2015. Patients were excluded if staging, treatment details, recurrence status, or smoking exposure in pack-years were not available. Two hundred and forty-four patients were included.

Results: Patients with 25 pack-years or greater smoking history exhibited a dose-dependent decrease in RFS compared to never smokers. This was robust to multivariate analysis for including staging and demographic factors. Forty-three patients with available targeted tumor sequencing data were identified. A strong trend was observed for increased C to A transversion mutations above 25 pack-years, which are known to be associated with exposure to tobacco smoke. Similarly, the proportion of COSMIC Signature 4 mutations were also found to be more common in patients with more than 25 pack-years of smoking exposure.

Conclusion: Evidence-based smoking exposure thresholds are needed to define inclusion criteria for trials of de-escalation therapy for p16+ OPSCC. Patients with smoking exposure greater than 20 pack-years have increased risk of recurrence and a distinct pattern of genomic alterations. Further studies are needed to delineate the potential consequences of mild smoking exposure. Smoking-related mutational signatures may hold potential for biomarker development in p16+ OPSCC.

Level of evidence: 2B.

Keywords: HPV; oropharyngeal squamous cell carcinoma; outcomes; smoking exposure.

FIGURE 1

RFS among p16+ OPSCC patients by smoking exposure level. (A) Hazard ratio of patients with smoking exposure above the threshold given by x‐axis (ie, exposure is greater than or equal to (>=) than this threshold, or strictly greater than (>) zero) as compared to non‐smoking patients (ie, exposure equals 0). Error bars represent the 95% confidence interval. All subgroups of patients with 25 pack‐years or greater were found to have significantly decreased RFS. (B) Kaplan‐Meier plots showing survival as stratified by smoking exposure groups. The symbol “*” indicates a significant decrease in RFS (log‐rank test, P < .05)

FIGURE 2

Genomic features of p16+ OPSCC tumors by smoking exposure level. (A) Genomic Features identified by the UNCseq targeted exome sequencing platform. Mutations—total number of high confidence variants per tumor. CN Events—total number of genomic copy‐number events detected by the SynthEx pipeline. MAD (VAF)—the MAD of the variant allele frequencies of all high confidence mutations per tumor. MAD (VAF)*100 is displayed for clarity. (B) C to A transversion mutations—as a function of smoking exposure. Boxplots—box represents IQR and whiskers include data within 1.5 (IQR)

FIGURE 3

COSMIC Signatures of p16+ OPSCC tumors by smoking exposure level. (A) Proportion of COSMIC signature 4 (associated with tobacco exposure) related mutations (y‐axis) as identified by R package deconstructSigs package, as a function of smoking exposure. X‐axis represents sliding cut‐off separating samples into “high” and “low” categories. (B) COSMIC signature 5 (mutagenic mechanism unknown) vs smoking exposure. Boxplots—box represents IQR and whiskers include data within 1.5 (IQR)