Oropharyngeal cancer patients with human papillomavirus (HPV) have a more robust response to radiation therapy

UC Davis cancer researchers have discovered significant differences in radiation-therapy response among patients with oropharyngeal cancer depending on whether they carry the human papillomavirus (HPV), a common sexually transmitted virus. The findings could lead to more individualised radiation treatment regimens, which for many patients with HPV could be shorter and potentially less toxic.
HPV-related cancers of the oropharynx (the region of the throat between the soft palate and the epiglottis, including the tonsils, base of tongue and uvula) have steadily increased in recent years, according to the National Cancer Institute, especially among men. At the same time, the incidence of oropharyngeal cancers related to other causes, such as smoking or alcohol consumption, is declining. HPV is the most common sexually transmitted infection in the United States; it can spread through direct skin-to-skin contact during vaginal, anal and oral sex.
The UC Davis study, conducted by Allen Chen, associate professor in the UC Davis Department of Radiation Oncology, examined patterns of tumour reduction during radiation treatment in two otherwise similar groups of patients with oropharyngeal cancer: those who tested positive for HPV and those who tested negative for the virus. None of the HPV patients in the study was a smoker, a leading risk factor for the disease.
Chen used CT scans acquired during image-guided radiation therapy (IGRT) and endoscopy (a tube with a small camera) to capture 3D images of the patients’ tumours and monitor their treatment progress. He found that within the first two weeks after starting radiation, the gross tumour volume decreased by 33 percent in HPV-positive patients, while the volume decreased by only 10 percent in HPV-negative patients.
Chen said the results demonstrate that HPV-positive patients have a more rapid and robust response to radiation treatments, confirming what clinicians have suspected for years.
‘These HPV-related tumours literally melt before your eyes,’ he said. ‘It is very gratifying to tell patients early on during treatment that their tumours are responding so quickly. Most of them are pleasantly relieved to hear such news.’
The rapid rate of tumour regression did not continue, however, after the second week of radiation treatment, and by the end of the seven-week regimen, the total tumour shrinkage in both groups of patients was nearly the same.
However, ‘the dramatic early response observed in the HPV-positive patients strongly implies that these tumours behave distinctly from a biological standpoint and could be approached as a separate disease process,’ Chen said.
For example, the findings suggest that treatment for HPV-positive cancer may not need to be as intensive for it to be effective, Chen said, adding that a shorter, abbreviated treatment regimen would potentially lessen the side effects from radiation, which include sore throat, dry mouth, taste loss and swallowing difficulties.
‘It is likely that treatment in the future will be individualised based on biomarkers present in the tumour, and HPV has the potential to do just that,’ said Chen.
Chen said there is increasing evidence that HPV-positive patients who receive radiation treatments live longer and have higher cure rates. According to the NCI, 88 percent of the HPV-positive patients are still alive two years after their treatments, compared with 66 percent of the HPV-negative patients.
‘Given the impressive outcomes for patients with HPV-positive cancer using currently aggressive treatments, how to de-intensify therapy while maintaining cure rates is definitely a hot topic right now,’ said Chen. UC Davis Comprehensive Cancer Center