Responses to radiation therapy are significantly different among patients with oropharyngeal cancer, depending on if they carry the human papillomavirus (HPV). More individualized radiation treatment regimens could result from these findings, according to a recent study.

The rates of HPV-related cancers of the oropharynx have steadily increased in recent years, especially among men. The incidence of oropharyngeal cancers that are related to other causes, such as smoking or alcohol consumption, is currently declining. HPV is the most common sexually transmitted infection in the United States, and it can spread through direct skin-to-skin contact during vaginal, anal, and oral sex.

This study, published in The Laryngoscope Journal, examined patterns of tumor reduction during radiation treatment in two otherwise similar groups of patients with oropharyngeal cancer. One group tested positive for HPV and the other group tested negative. None of the HPV patients in the study were smokers, which is a leading risk factor for the disease.

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Allen Chen, associate professor in the UC Davis Department of Radiation Oncology, conducted the study. He used CT scans that were acquired during image-guided radiation therapy and endoscopy to capture three-dimensional images of the patients’ tumors and to monitor their treatment progress. Within the first 2 weeks of radiation therapy, the gross tumor volume decreased 33% in the HPV-positive patients, while tumor volume decreased only 10% in the HPV-negative patients.

“These HPV-related tumors literally melt before your eyes,” Chen said. “It is very gratifying to tell patients early on during treatment that their tumors are responding so quickly. Most of them are pleasantly relieved to hear such news.” However, the rapid rate of tumor regression did not continue after the second week of radiation treatment. By the end of the 7-week regimen, both groups of patients had nearly identical total tumor shrinkage.

“The dramatic early response observed in the HPV-positive patients strongly implies that these tumors behave distinctly from a biological standpoint and could be approached as a separate disease process. It is likely that treatment in the future will be individualized based on biomarkers present in the tumor, and HPV has the potential to do just that. 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,” Chen said.

Chen and his colleagues have launched a clinical trial of HPV-positive oropharyngeal cancer patients that will evaluate outcomes when radiation doses are reduced from 7 weeks to either 5 or 6, depending on their response to initial chemotherapy. This trial at UC Davis has just recently opened enrollment.