Surgery and Reducing Ionizing Radiation of the Unknown Primary

Approximately 3% of all head and neck squamous cell carcinoma (SCC) patients present with nodal disease from an unknown primary (PUK). The incidence of PUK has increased in tandem with the rise of human papillomavirus (HPV)-mediated oropharyngeal SCC (OPSCC). HPV-mediated PUK now represents at least half of the head and neck PUK population, with an excellent prognosis and approximately 90% 5-year overall survival (OS).

The work-up for PUK has significantly improved with the introduction of positron emission tomography (PET) imaging and transoral robotic surgery (TORS). PET identifies at least 40% of primaries in PUK patients when clinical and radiological work-up is negative, and TORS has a higher primary identification rate (70%-80%). Current guidelines recommend tonsillectomy and tongue base mucosectomy in the work-up of PUK patients.

Definitive management of HPV-mediated PUK remains controversial, with curative options including primary neck dissection ± adjuvant therapy or primary radiotherapy ± concurrent chemotherapy. Treatment morbidity is significant, despite the excellent outcomes (90% 5-year OS). Key issues include the choice of initial treatment modality and whether to treat mucosal surfaces with radiation prophylactically.

Current guidelines recommend single-modality surgery (neck dissection) for low-volume neck disease. This recommendation is based on studies suggesting low primary emergence rates (1.5%-7%) and outcomes comparable to non-surgical treatment paradigms. Evidence from early-stage OPSCC supports surgery alone as a safe option for HPV-mediated PUK.

A critical question is whether to irradiate mucosal surfaces when using radiotherapy for HPV-mediated PUK. Emerging data suggest that omitting mucosal radiation has a very low risk (<5%) of primary tumour emergence, potentially improving long-term quality of life and reducing toxicities like dysphagia and xerostomia. Several retrospective studies support the safety and reduced toxicity of involved neck radiotherapy without mucosal irradiation.

This trial is specifically designed with an upfront neck dissection alongside tonsillectomy and tongue base mucosectomy. Combining an upfront therapeutic neck dissection with the final stage of the diagnostic work-up has several benefits. Surgically treating the neck in selected patients during tonsillectomy and tongue base mucosectomy accelerates treatment, avoids additional delays, reduces costs to healthcare institutions, and prevents the need for a second surgery if no primary is identified. The addition of neck dissection to tonsillectomy and tongue base mucosectomy also involves relatively minor additional surgical morbidity in the context of a patient already undergoing pharyngeal surgery. In some instances, upfront surgical treatment of the neck may complete definitive treatment at the earliest opportunity. Patients with intermediate-volume neck disease, who require dual-modality treatment, also benefit from no further surgical delay and can proceed to radiotherapy following a single surgical encounter. An upfront neck dissection is also the gold standard for lymph node evaluation and may down-stage patients into a unimodality approach, thereby avoiding additional toxicity. For example, if imaging suggests multiple involved ipsilateral nodes in an HPV-mediated PUK patient, conventional treatment would involve dual-modality therapy. Pathological staging may down-stage this patient into a unimodality paradigm, sparing them significant toxicity.

In this randomized phase II trial, the study team hypothesizes that omitting mucosal radiation will lead to improved quality of life, decreased toxicity, and low rates of primary tumour emergence. Further, the researchers hypothesize that neck dissection alone for low-volume HPV-mediated PUK will result in excellent oncologic and functional outcomes.

The main objective is to assess the impact of omitting mucosal radiation on oncologic outcomes, toxicity, functional outcomes, and quality of life (QOL) in patients with p16-positive PUK.

The primary endpoint is to determine the rate of primary emergence of a mucosal p16-positive SCC in the upper aerodigestive tract compared to historical controls.

The secondary endpoints include:

Quality of life (using MDADI, EORTC QLQ-C30 and H&N35, EQ-5D-5L, NDII) Overall survival (OS) Disease-free survival Regional recurrence within the neck Distant recurrence outside the upper aerodigestive tract and neck levels Rate of salvage treatment for primary emergence Rate of unsalvageable primary emergence Rate of percutaneous feeding tube insertion and use at 1 year Swallowing function (DIGEST score, FOIS) Toxicity (CTCAE version 5) Patients will be randomized 1:2 between the standard of care (Arm 1) and omission of radiation to mucosal surfaces (Arm 2).

Combining neck dissection with tonsillectomy and tongue base mucosectomy accelerates treatment, reduces costs, and avoids additional surgery. This approach involves minor additional surgical morbidity and can complete definitive treatment at the earliest opportunity. Upfront neck dissection also allows for accurate lymph node evaluation and potential down-staging, thereby sparing patients from additional toxicity.

The SUPERIOR trial aims to determine whether omitting mucosal radiation improves quality of life and reduces toxicity in HPV-mediated PUK patients, while evaluating the efficacy of neck dissection alone for low-volume disease. The study seeks to establish evidence-based guidelines for the optimal management of HPV-mediated PUK.

Inclusion criteria

for the Registration phase

• p16 positive PUK SCC of the neck
• Age 18 years or older
• Willing to provide informed consent
• Eastern Cooperative Oncology Group (ECOG) performance status 0-2
• Clinical nodal stage N1, AJCC 8th edition (i.e. clinical unilateral nodal disease, none larger than 6 cm)
• Complete clinical work-up, including CT neck, physical examination with nasopharyngoscopy, and PET/CT, with no evidence of a primary tumor. The PET/CT scan must be without focal metabolic activity concerning for a primary tumor, in the opinion of the nuclear medicine physician. Metabolic activity, particularly in the tonsils and base of the tongue which is within normal physiologic range, does not exclude participation.

Inclusion criteria

for the Randomization phase

• Completed ipsilateral tonsillectomy and base of tongue mucosectomy with no evidence of a primary tumor

o Note, patients who had a PET/CT that was initially positive, and therefore not meeting criteria in 4.10, but panendoscopy with biopsies of the fluorodeoxyglucose (FDG)-avid areas do not show malignancy, can then be enrolled and would be returned the OR for a neck dissection prior to randomization

• Ipsilateral nodal disease on pathology with no evidence of extranodal extension

Exclusion criteria

• Radiological or pathological extra-nodal extension
• Epstein-Barr Virus (EBV)-positive
• Clinical nodal stage (i.e. before neck dissection) N2-3, AJCC 8th edition (ie. bilateral nodes or node >6cm)
• Pathological nodal stage (i.e. after neck dissection) pN3
• Prior history of head and neck cancer within 2 years
• Any other active invasive malignancy, except non-melanotic skin cancers, low-risk prostate cancer, and stage I-IVA papillary or follicular thyroid cancer
• Known metastatic disease
• Unable to complete QOL questionnaires
• Pregnant or lactating women