In current diagnostic work-up of patients with a cancer of unknown primary (CUP), approximately 50% of the primary tumor lesions remains undetected. Identification of the primary tumor site results in minimizing the potential morbidity from treatment by reducing morbidity by omitting the need for a mucosectomy of the bilateral base of tongue and tonsils, reducing the radiation field and better oncologic outcome than those with unidentified primary tumor. Clearly, new endoscopic 'real-time' imaging techniques are needed to visualize mucosal changes associated with head and neck squamous cell carcinoma and increase detection rate of the primary tumor. Targeted fluorescence endoscopy enables the visualization of targeted tumor-specific biomarkers by using fluorescence, thereby enhancing the contrast between normal mucosa and tumor tissue. This could improve the detection of the primary tumor in cases where the primary tumor is not detected with white light endoscopy.

Inclusion Criteria:

• Cytology and/or histology-confirmed diagnosis of squamous cell carcinoma most likely originating from the head & neck area and scheduled to undergo endoscopy of the upper aerodigestive tract as decided by the multidisciplinary head and neck tumor board of the UMCG;
• The primary tumor was not identified during standard diagnostic work-up in the outpatient clinic including physical head and neck examination, fiberoptic laryngoscopy, chest X-ray, CT and PET/CT;
• Age ≥ 18 years;
• Written informed consent;

Exclusion Criteria:

• Medical or psychiatric conditions that compromise the patient's ability to give informed consent;
• Concurrent uncontrolled medical conditions;
• Received an investigational drug within 30 days prior to the dose of cetuximab-800CW;
• History of myocardial infarction, cerebrovascular accident, uncontrolled cardiac heart failure, significant liver disease (ALT >3X upper limits of normal or increased total bilirubin) or unstable angina within 6 months prior to enrollment;
• Inadequately controlled hypertension with or without current antihypertensive medications;
• History of allergy or infusion reactions cetuximab or other monoclonal antibody therapies;
• Pregnant or lactating women. Documentation of a negative pregnancy test must be available for women of childbearing potential. Moreover, the need to be willing to ensure that she or her partner uses effective contraception during the trial and for 6 months thereafter. Woman of childbearing potential are premenopausal women with intact reproductive organs and women less than two years after menopause;
• Evidence of QT prolongation on pretreatment ECG (greater than 440 ms in males or greater than 450 ms in females)
• Patients receiving Class IA (quinidine, procainamide) or Class III (dofetilide, amiodarone, sotalol) antiarrhythmic agents.
• Life expectancy < 12 weeks;
• Karnofsky performance status < 70%.