950P Prognostic and predictive value of skeletal muscle mass (SMM) in squamous cell carcinoma of the head and neck (SCCHN) in patients treated with immune checkpoint inhibitors (ICI)

SMM has been associated with increased treatment related acute toxicity and complications in several tumour types. However, there is no reported evidence of this association in SCCHN patients treated with ICI. We explored whether low SMM influenced the onset of severe toxicity and prognosis in these patients. We conducted a retrospective cohort study of all patients diagnosed with recurrent or metastatic SCCHN treated with ICI and evaluated with CT scan between July 2015 and December 2018. SMM was estimated using a computed tomography scan through cross-sectional image analysis at the level of the third lumbar vertebra (L3). Patients were classified into two groups: low SMM vs non-low SMM using cut-off points previously published. Toxicity was recorded using Common Terminology Criteria for Adverse Events v4.03. 65 patients were enrolled; 56 men (86.23%), mean age of 57.7 years (SD 9.38), mainly hypopharynx (n=28; 43.1%). Forty-six (70.8%) patients had low SMM before starting ICI. No significant differences in progression free survival (PFS) were observed between both groups (P= 0.194), although patients with low SMM were more likely to have progressive disease compared to non-low SMM (56.8% vs 47.4%). Among patients with baseline low and non-low SMM, median overall survival was 7.9 and 18 months, respectively. Patients with low SMM also had a worse one-year survival (HR 0.94; 95% CI:0.9, 0.99; P=0.009). Patients who died during the study had a mean baseline SMM 3 cm2/m2 lower than those that were alive at the end of the treatment. Treatment-related adverse events of any grade occurred in 34 patients (56.7%). No significant difference was observed in the development of toxicity according to SMM at baseline (P=0.616). However, grade 3-4 toxicity was developed in 7 patients, of whom 6 had low baseline SMM. This preliminary report offers the opportunity to speculate about the negative influence of low baseline SMM and response to ICI. Further research is needed to confirm the role of body composition changes as a predictive biomarker in ICI treatment.