MTOR and neuroendocrine neoplasm: Rapamycin is used to treat renal cell cancer, neuroendocrine tumors and metastatic breast cancer by inhibiting mammalian target of rapamycin (mTOR) activation.(23) Bryostatin and epothilone have also been used to treat cancer, and many other macrolides, such as exiguolide, are under investigation.(24) Among macrolides, EM has the fewest side effects.