Recovery of salivary epidermal growth factor in parotid saliva following parotid sparing radiation therapy: a proof-of-principle study

BackgroundAlthough radiation therapy (RT) causes permanent xerostomia, parotid-sparing radiation therapy (PSRT) ensures recovery of saliva quantity over time. Salivary epidermal growth factor (EGF) is produced primarily by parotid glands.ObjectivesThe aim of this study was to determine whether salivary EGF can be detected in parotid saliva after PSRT and whether protein secretion is time dependent.Study designSalivary EGF concentration (pg/mL) was determined by enzyme-linked immunosorbent assay in stimulated parotid saliva before RT and at 3, 6, and 12 months after RT from 22 patients with head and neck cancer treated with PSRT.ResultsSaliva samples were from 17 men and 5 women (age ranges 23-70 years and 46-71 years, respectively). At 6 months after RT, EGF concentration was 407 pg/mL lower than at baseline (P = .045). Twelve months after PSRT, parotid glands produce substantial amounts of EGF and other proteins, eventually approximating pre-RT levels, with recovery of salivary function.ConclusionsThis proof-of-principle study shows that even proteins in picogram quantities, such as EGF, can be detected in saliva after PSRT.