Patients will be block randomized 1:1 into two cohorts: treatment with zafirlukast and the standard of care, or standard of care alone. Patients will begin treatment with zafirlukast on post-operative day one following placement of tissue expander(s) once determined safe from a surgical recovery standpoint. They will be continued on the standard dosing (20mg PO twice per day) of zafirlukast through expander fill (6-12 weeks, up to 18 weeks for women receiving radiation). Treatment will be stopped 48 hours prior to expander-implant exchange, which is equivalent to 5 half-lives of the drug. Patients will be seen every 1-2 weeks for expander fill, and will be assessed clinically based on the Baker classification system of capsular contracture at every appointment. The day of surgery for their expander-implant exchange, their Baker classification will also be noted.