Three new macrocyclic trichothecenes (1-3) and five known related compounds (4-8) were isolated from the MeOH extract of a plate culture of the fungus Podostroma cornu-damae, a deadly poisonous mushroom. Miophytocen D (1) is a rearranged macrocyclic type D trichothecene, featuring a bicyclo-[6.5]dodecahydrocyclopenta[ b]chromene scaffold, and the structures of new compounds (1-3) were delineated by the combination of 1D and 2D NMR spectroscopic experiments and HRESIMS, modified Mosher's esterification, and quantum chemical ECD calculations. The isolated compounds (1-8) were evaluated for cytotoxicity against four human breast cancer cell lines (Bt549, HCC70, MDA-MB-231, and MDA-MB-468). Compounds 4, 6, and 8 exhibited significant cytotoxic effects against the breast cancer cell lines, with IC50 values in the range of 0.02-80 nM, which is stronger than doxorubicin, the positive control, and a structure-activity relationship was suggested.