Noninfectious pneumonitis with the use of mTOR inhibitors in breast cancer

The mammalian target of rapamycin (mTOR) inhibitor class of drugs represents the newest addition to the armamentarium of therapies for hormonally driven breast cancer. It has recently been shown that the addition of mTOR inhibitor everolimus to aromatase inhibitors in hormone receptor–positive breast cancers improves progression-free survival. However, a clinically significant toxicity associated with this class of drugs is the development of noninfectious pneumonitis (NIP). Although generally mild and manageable, everolimus-induced NIP requires prompt diagnosis and management. This article will provide a brief overview of data relating to dysregulation of the phosphatidylinositol-3-kinase/protein kinase B/mTOR pathway in breast cancer; review the literature relating to the efficacy and safety of mTOR inhibitors in breast cancer; and evaluate the incidence, severity, and optimal management of mTOR inhibitor–related NIP in breast cancer.