Human papillomavirus (HPV)-related oropharyngeal carcinoma are exquisitely radiosensitive. Several studies attempted to reduce the toxicities of treatments through reduced-dose radiation and showed promising results, but all data were collected from non-Chinese areas. Like nasopharyngeal carcinoma (NPC), oropharyngeal carcinoma may have different biological behavior and relationship with HPV infection. So the investigators studied whether toxicities reducing treatment with reduced radiation dose and omitted concurrent chemotherapy after good response to induction chemotherapy would maintain survival outcomes while improving tolerability for patients with HPV-positive oropharyngeal carcinoma. Immune checkpoint inhibitors (ICIs) have proved to improve outcomes of head and neck cancers including EBV-related NPC. Oropharyngeal carcinoma was considered to be similar with NPC in terms of immune environment. So we added anti-PD-1 antibody Toripalimab to induction chemotherapy in order to achieve better response rates to receive de-escalation chemoradiotherapy followed.

Inclusion Criteria:

• Histological diagnosis of squamous cell carcinoma of oropharynx with IHC p16
• positive or PCR HPV16 positive
• T1-2/N1-3M0（except T1N1M0 and single LN<3cm）or T3-4N0-3M0 according to UICC/AJCC 8th staging system
• Age ≥18
• No prior anti-tumor treatment
• Karnofsky Performance Score (KPS)≥70
• Adequate blood supply
• Informed consent obtained

Exclusion Criteria:

• Cannot take contrast-MRI imaging
• Pregnant
• Combined with other malignant tumor (except basal cell carcinoma of skin)