This phase III trial studies how well dexamethasone works in reducing everolimus-induced oral stomatitis in patients with cancer. Dexamethasone may help to reduce the everolimus-induced oral stomatitis so as to improve quality of life in cancer patients.

PRIMARY OBJECTIVES: I. To determine if the initiation of dexamethasone at the start of everolimus treatment prevents mTOR inhibitor-associated stomatitis (mIAS)-associated pain, compared to the initiation of placebo. II. To determine if the initiation of dexamethasone at the start of everolimus treatment will be superior compared to the initiation of placebo in terms of the overall severity of mIAS-associated pain. SECONDARY OBJECTIVES: I. To utilize the same measurement method that was reported in the SWISH trial: A combination of a patient reported pain scale, data from a normalcy of diet questionnaire, and clinician grading of stomatitis to determine the incidence of \> grade 2 mIAS. II. To determine if the initiation of dexamethasone at the start of everolimus increases time to development of mouth pain using daily numerical analog scale patient-reported data collection. III. To assess if quality of life is better when dexamethasone mouth rinse use starts at the same time as everolimus use versus at the time when mouth pain begins. IV. To investigate if starting dexamethasone mouth rinse concurrent with starting everolimus improves patients' ability to adhere to everolimus therapy. V. To compare dexamethasone prescription fill rates and timing between patients who received placebo versus study drug at the initiation of everolimus. Trial Design: OUTLINE: Patients are randomized to 1 of 2 groups. GROUP I: Patients receive everolimus orally (PO) once daily (QD) as standard of care and dexamethasone as mouthwash over 2 minutes 4 times per day (QID) for 8 weeks. GROUP II: Patients receive everolimus PO QD as standard of care and placebo as mouthwash over 2 minutes QID for 8 weeks.