151751-Najiba-Chargi

274 CHAPTER 15 ABSTRACT Background Low skeletal muscle mass (SMM) is associated with toxicities and decreased survival in head and neck cancer (HNC). Chemoradiotherapy (CRT) may exaggerate loss of SMM. We investi - gated the changes in SMM, their predictors and prognostic impact of SMM in patients treated with CRT between 2012 and 2018. Material and methods Skeletal muscle area (SMA) segmentation was performed on pre- and post-CRT imaging. Ob - served changes in SMM were categorized into: (I) stable (II) moderate gain (III) moderate loss (IV) large gain and (V) large loss. Results In total, 235 HNC patients were included of which 39% had stable SMM, 55% moderate loss, 13% moderate gain, 0.4% large loss and 0.4% large gain of SMM. After CRT, SMA decreased compared to pre-CRT (31.6 cm 2 versus 33.3 cm 2 , p<0.01). Key predictors were a body-mass index (BMI) of ≥25 or ≥30kg/m 2 (HR 2.4, p<0.01 and HR 3.1, p<0.05, respectively), oropharynx tumor (HR 2.4, p< 0.05), albumin level (HR 1.1, p<0.01) and postoperative CRT (HR 0.39, p<0.01). Conclusion Low SMM and SMM changes were not prognostic for survival. Loss of SMM is highly prevalent after CRT and the aforementioned variables may aid in identifying patients at risk.