2ABSTRACT PURPOSE Radiotherapy induced xerostomia (RIX) is the most common permanent side effect of radiotherapy (RT) to the head and neck (H&N). There is no effective topical treatment. LMS-611 is a mimetic of a natural lamellar body which prevents thick secretions like saliva from congesting organs. Primary objective -assess saliva properties before and during RT to the H&N. Secondary objectives -re-assess saliva properties with the addition of LMS-611, measure inter-patient variability, correlate patient reported symptoms with laboratory measurements and design subsequent first-in-human clinical trial of LMS-611. METHODS Patients with H&N cancer receiving RT as primary treatment were recruited. Patients completed the Groningen RIX (GRIX) questionnaire and provided saliva samples at baseline, weeks 2, 4 and 6 of RT. Saliva adhesiveness and viscosity was tested by measuring time taken to travel 5cm down an inclined plane. RESULTS 30 patients were enrolled. The inclined plane test (IPT) results (seconds) were as follows: baseline 31.3, week-2: 49.7, week-4: 51.1, week-6: 55.7. Wide inter-patient variability was seen at baseline. GRIX scores increased as RT progressed. Spearman rank correlation coefficient of inclined plane tests with GRIX scores was -0.06 at baseline, week-2 0.25, week-4 0.12 and week-6 0.08. LMS-611 concentrations of 10mg/ml and 20mg/ml significantly reduced IPT times on saliva samples. CONCLUSIONS Saliva becomes more visco-adhesive and RIX worsens as RT progresses. There is little correlation between objective and subjective measures of RIX. The addition of LMS611to thick, sticky saliva restores its fluidity ex-vivo. This warrants in-vivo analysis of the effect of LMS-611 upon RIX.