Pathological and Virological Studies of p16-Positive Oropharyngeal Carcinoma with a Good Response to Neoadjuvant Chemotherapy.

Human papillomavirus (HPV)-related, p16-positive oropharyngeal carcinoma is considered to be sensitive to anticancer drugs, and the standard treatment is therefore chemoradiotherapy, rather than surgery, especially for aggressive disease. However, with this higher sensitivity, chemotherapy alone may achieve a pathological complete response (CR), making radiation therapy unnecessary. A 46-year-old man with p16-positive squamous cell carcinoma (SCC) of the lateral oropharynx (palatine tonsil) underwent neoadjuvant chemotherapy. This achieved clinically significant tumor shrinkage and therefore surgery was performed for subsequent definitive treatment. Clinical and CT findings indicated a good effect of neoadjuvant chemotherapy on the tumor. A biopsy prior to chemotherapy revealed SCC, which demonstrated p16 immunoreactivity and positive signals for high-risk HPV by RNA in situ hybridization. The post-chemotherapy surgical specimen showed pathological CR and no p16 positive cells nor positive signals for high-risk HPV those were detected in the pre-chemotherapy specimen. There are some reports of chemotherapy alone achieving pathological CR in cases of p16-positive oropharyngeal carcinoma, but none have included high-risk HPV RNA findings. This is the first report of the disappearance of cancer cells as well as p16 staining and a positive signal for high-risk HPV. Achieving pathological CR confirmed by immunohistochemistry and high-risk HPV RNA in situ hybridization in a solid tumor with chemotherapy alone suggests that chemotherapy may have both an antitumor effect and an antiviral effect. Forgoing subsequent radiotherapy and undergoing surgery might be unnecessary and follow-up instead might be sufficient in such cases. Into the future, in an optimal tailored treatment approach, the option of neoadjuvant chemotherapy should be considered for management of p16-positive oropharyngeal carcinoma. Other options such as tumor immunotherapy are also expected to be effective.