Patients with HPV-positive oropharyngeal squamous cell cancer (OPSCC) who smoke can develop tobacco-associated mutations over time. These accumulated mutations result in less dependence on E6/E7 and other HPV-associated mutations.
The number of HPV viral reads was inversely associated with smoking and survival status.
“Patients who smoke and patients who were deceased from their cancer had a lower number of HPV viral reads,” said Jose P. Zevallos, MD, assistant professor, director of Oncologic Research, Head and Neck Surgical Oncology, University of North Carolina (UNC), Chapel Hill.
“This means that, potentially, the tumors began as HPV-driven, but over time developed subclones that were driven by tobacco-associated gene mutations as a result of exposure to smoking.”
The study used targeted next-generation sequencing analysis of over 800 genes in 66 cases of HPV-positive OPSCC. Patients were stratified by smoking status, either as >10 pack-years (40 patients) or <10 pack-years (26 patients). The patient data came from a North Carolina population-based epidemiological study that was conducted from 2001 to 2006. The mutations were measured against the Catalogue of Somatic Mutations (COSMIC), which is an online database of somatic mutation data that is maintained by the Sanger Institute as part of its Cancer Genome Project.
Zevallos explained that HPV-positive OPSCC, compared with HPV-negative OPSCC, has an excellent prognosis. However, among patients with HPV-positive OPSCC, smokers have a worse 5-year survival rate than never smokers.
This study sought to understand outcomes in patients with exposure to both HPV and tobacco. Previous work had shown that patients with exposure to both have an intermediate outcome relative to tumors that are HPV-negative and tobacco-driven versus never-smokers.
The mutational analysis found that heavy or ever smokers had tobacco-associated mutations that occurred almost exclusively in this group. The heavy smoking group had more HLA-A mutations, which are related to inflammation. Mutations associated with tobacco exposure and poor survival had an almost exclusive occurrence in the heavy smoker group. These mutations included TP53 (6% in >10 pack-year smokers vs 0% in <10 pack-year smokers; P = .428), CDKN2A (2% vs 0%; P = .758), FAT1 (14% vs 6%; P = .688), CASP8 (8% vs 0%; P = .565), NOTCH1 (18% vs 0%; P = .092), FGFR3 (10% vs 0%; P = .325), and KRAS (4% vs 0%; P = .232) genes.
The differences in gene mutations related to immunity and tobacco use may explain why smokers have more aggressive HPV-positive cancer, according to Zevallos.
Among the 66 patients, 95% had HPV 16 DNA, 3% had HPV 35, and 1% had HPV 58. The mean number of HPV reads per sample was 838,520. The number of reads varied by both survival and smoking status, with lower HPV reads associated with both worse survival and heavier smoking status.
The study concluded that the lower number of HPV reads associated with smoking and poor survival may suggest accumulation of tobacco-associated mutations. These mutations may lead to less dependency on E6/E7 and HPV-mediated oncogenesis. The authors hypothesized that the HPV-positive signature, perhaps from a PI3K pathway mutation as an initiating event, may be maintained as HPV-positive smokers acquire mutations in tobacco-related genes.
“This study will have important implications for personalizing treatment and decision making for HPV-positive oropharyngeal cancer, particularly in the era of less aggressive treatment for HPV-positive tumors with their excellent prognosis,” said Zevallos. “As opposed to deciding that 10 pack-years is a number that we use to define more aggressive disease, we are trying to define a molecular basis for more aggressive disease in order to decide who would benefit from less aggressive versus more aggressive treatment.”
Zevallos stated that tobacco-associated mutations are more detrimental than HPV-associated mutations. He added that adding tobacco to HPV worsens OPSCC outcomes.
A larger study of HPV-positive oropharyngeal cancer using DNA and RNA sequencing technologies is currently being conducted at UNC. Its goal is to define high-risk HPV-positive OPSCC.