A multi-centre validation study to evaluate whether a new imaging and surgical protocol would work as well as the current gold standard in identifying sentinel nodes in patients with oropharyngeal cancer.

Cancer at the back of the mouth and throat is usually discovered after it has spread to lymph glands in the neck. Treatment therefore involves dealing with both the original tumour (in the mouth/throat) and the spread cancer in the lymph glands. This type of cancer sometimes spreads to both sides of the neck, not just the side on which the original tumour was located. The decision as to whether to treat the other side of the neck as well depends on various factors including the aggressiveness of the tumour, whether the patient smokes and whether or not the Human Papilloma Virus (HPV) is present in the tumour. This is inevitably inexact, and assessing the likelihood of the cancer spreading to the other side of the neck always involves an element of estimation. Some patients end up being treated unnecessarily on both sides (often with severe and lasting effects on swallowing, meaning they have to use a feeding tube), while others receive treatment on one side only but the cancer comes back on the other side.

This study will provide more accurate information on which to base the decision as to whether to treat the other side of the neck. The study will use a procedure known as sentinel node biopsy (SNB) to establish (with a high degree of accuracy) whether or not the cancer has spread to the other side of the neck. The study will be in two stages. The first stage is the imaging stage. A very low does of a radioactive tracer substance will be injected into the tumour. The radioactive tracers used in this study are either Human albumin colloidal particles or Lymphoseek. Once injected, they move quickly into the lymph nodes and can then be detected using a handheld gamma camera. The first nodes that the radiotracer moves into are the "sentinel" nodes. Patients already undergo an examination under anaesthetic (EUA); the patients participating in the study will have the radiotracer injected additionally and the sentinel nodes detected during this EUA. The use of the handheld camera is relatively new; so, all of the patients in the study will also have a CT scan the next day to double check whether the handheld camera identified the sentinel nodes correctly. The second stage of the study, the surgery stage, will involve a new group of patients having the imaging procedure. Those who do have sentinel nodes in the other side of the neck will have them removed during the EUA. Those nodes will then be examined thoroughly for signs of cancer. A separate limb of stage one of the study will involve some patients whose main tumours are easily accessible also having their tumour injected with the radiotracer a second time under local anaesthetic in an outpatient clinic. In the study this will take place several days after the initial injection with the radiotracer. If this procedure is found to be acceptable to patients, it would mean that patients could have the radiotracer injected before the EUA, thereby allowing time for the sentinel nodes to be identified by CT scan so that they can be removed during the EUA. This will provide a way to ensure that, even if the handheld camera cannot be used, the sentinel nodes can still be removed while the patient is under anaesthetic for the EUA. If the study is successful, the patient will be able to have much more accurate information about whether their cancer has, or might, spread to the other side of the neck, without having to undergo an additional general anaesthetic.

Inclusion Criteria:

• Adults aged 18 or over
• New diagnosis of OPC - all anatomical subsites and HPV status accepted
• Unilateral metastatic nodes equating to AJCC TNM8 clinical staging N1-N2b for P16 negative and N1 for P16 positive patients.

Exclusion Criteria:

• Suspicious bilateral nodes on imaging
• Previous radiotherapy or surgery to the neck
• Second primary oropharyngeal tumours
• Distant metastasis (e.g. lung, bone)
• Pregnancy and lactation
• Inability to give informed consent
• Allergy to lymphatic tracers

No identifiable data will be shared with anyone outside the study