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296 CHAPTER 16 vertebra (L3) is very common in oncological research 17 , this may lead to an inclusion bias in HNC patients because not all patients will undergo a PET-CT during the diagnostic work-up. 24 Recently, a novel SMM assessment method at the level of the third cervical vertebra (C3) was published. 25,26 Imaging at the level of C3 is almost always available in HNC patients because diagnostic imaging of the head and the neck area is used for staging, which allows the routine assessment of SMM. In this study, we aim to investigate the prevalence and prognostic value of pre-treatment low SMM and sarcopenic obesity as measured at the level of C3 in a large cohort of OPSCC patients corrected for known prognostic factors including age, weight loss 6 months prior to diagnosis, comorbidities, HPV-status, and TNM-stage. MATERIAL AND METHODS ETHICAL APPROVAL The design of this study was approved by the Medical Ethical Research Committee of the University Medical Center Utrecht (approval ID 17-365/C). All procedures in this study were in accordance with the ethical standards of the institutional and/or national research commit- tee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. All data were handled according to general data protection regulation (GDPR). PATIENTS AND STUDY DESIGN A retrospective cohort study was conducted in 241 OPSCC patients diagnosed and treated with curative intent at the University Medical Center Utrecht, Utrecht, The Netherlands, be - tween 2009 and 2016. Patients with OPSCC were included if they had recent (≤ 1 months prior) pre-treatment imaging scans (CT or MRI) of the head and neck at the level of the third cervical vertebrae (C3). The median time between imaging and treatment was 0.79 month (IQR 0.56- 1.12). Patients were excluded if they had a palliative treatment intent (n=17) or if diagnostic imaging was of poor quality which impaired measurements of SMM (n=8). In total, 216 OPSCC patients were included. Relevant demographic and clinical variables were collected from patients’ medical record. Demographic variables included sex and age at diagnosis. Clinical variables included; length and weight at diagnosis, body-mass-index (BMI), percentage of weight loss in the six months prior to diagnosis, smoking status, amount of pack-years, alcohol intake, comorbidities as expressed by the Adult Comorbidity Evaluation-27 (ACE-27) score, tumor localization, date of histologic diagnosis, HPV-status, tumor staging according to the tumor-node-metastasis (TNM) 7th Edition IUCC manual, treatment modality (chemotherapy, radiotherapy, surgery or a combination) and survival data. HPV-status was determined using the algorithm described by Smeets et al: a p16 staining was performed. In case of a positive result this was followed by a PCR on HPV. 27 Patients with known HPV-status were stratified into risk groups as described by Ang et al: HPV-positive patients with less than 10 pack-years or with more than 10-pack-years but a N0-N2a nodal stage were considered to be at low risk,