S572
Clinical – Head & neck
ESTRO 2026
Cancer of Unknown Primary (CUP) presenting as lymph node metastases from squamous cell carcinoma in the head and neck (HNCUP) accounts for <10% of head and neck malignancies. Despite extensive diagnostics, the optimal treatment strategy in terms of surgery, radiotherapy, and/or systemic therapy remains matter of debate due to a lack of prospective data. Retrospective data are relatively limited.The purpose is to retrospectively analyze outcomes of HNCUP patients treated with radiotherapy. The primary endpoint is local and/or regional control. Secondary endpoints include overall survival (OS), disease-free survival (DFS), disease- specific survival (DSS), incidence of distant metastases, acute grade (G) ≥ 2 (<3 months) and late (up to 24 All patients were treated with radiotherapy for HNCUP in our hospital between December 2002-March 2024. Patients with distant metastases were excluded. All patients were re-staged according to the UICC 7th edition TNM classification. Survival data were analyzed using Kaplan-Meier curves (SPSS v29). OS, DFS, and DSS were assessed at 1, 2, and 5 years of follow-up. Toxicity was graded according to CTCAE criteria (v5.0). Results: 94 patients were included. 14 patients (14.9%) months) side effects. Material/Methods: experienced regional recurrence (13/14 within 5 years post-diagnosis), located in the high-dose region only (n=8), elective-dose region only (n=3), in both the high- dose and elective-dose region (n=1), in the neck outside the elective field (n=1) and unknown topography (n=1). One patient developed local recurrence in the floor of mouth outside the elective mucosal volume 5.5 months after end of radiotherapy. The 1, 2, and 5-year OS rates were 81.6%, 70.3%, and 56.8%, respectively. The 1, 2, and 5-year DFS rates were 73.1%, 63.3%, and 51.5%, respectively. The 1, 2, and 5-year DSS rates were 87.6%, 83.9%, and 78.2%, respectively. Distant metastases developed in 19 patients (20.2%, 10/19 pathologically confirmed), primarily in the lungs (12/19) and bones (8/19). Acute side effects (n=88) were frequent, most commonly xerostomia (37.5% G2, 1.1% G3), dysphagia (30.7% G2, 5.7% G3), and dysgeusia (taste loss, 23.9% G2, 1.1% G3). Chronic side effects decreased over time, but xerostomia (41.4% G1/G2) and fibrosis (29.3% G1/G2 of which 76% had surgery) remained the most prevalent late effects at 24 months.
Conclusion: PET/CT measurements of the salivary glands, particularly SUVMax and volume, can be used to non invasively monitor and predict xerostomia in HNC patients. Parotid glands contribute more significantly than submandibular glands, and integrating both ipsilateral and contralateral gland information yields the most accurate predictions. This approach offers a promising tool for xerostomia risk assessment and patient monitoring in clinical practice. References: [1] J. Castelli et al., « Weekly Adaptive Radiotherapy vs Standard Intensity-Modulated Radiotherapy for Improving Salivary Function in Patients With Head and Neck Cancer: A Phase 3 Randomized Clinical Trial », JAMA Oncol, vol. 9, no 8, p. 1056, août 2023, doi: 10.1001/jamaoncol.2023.1352.[2] L. Cubero et al., « Deep learning-based segmentation of head and neck organs at risk on CBCT images with dosimetric assessment for radiotherapy », Phys. Med. Biol., vol. 70, no 7, p. 075014, avr. 2025, doi: 10.1088/1361- 6560/adbf63.[3] Y. Li et al., « Validation of the 18F-FDG PET image biomarker model predicting late xerostomia after head and neck cancer radiotherapy », Radiotherapy and Oncology, mars 2023, doi: 10.1016/j.radonc.2022.109458. Keywords: Xerostomia, salivary flow, PET/CT imaging Digital Poster 1618 Cancer of unknown primary in the head and neck region: a retrospective study Andries Van den Berge, Sarah Deschuymer, Fréderic Duprez Radiation oncology, UZ Ghent, Ghent, Belgium
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