Hyperstable liposome comprising an anti-mitotic agent, one or more anions and one or more cations entrapped in the inner milieu, wherein the entrapped anti-mitotic drug is released at a slow rate that is less than 0.6% in 12 hours or less than 5% in 8 hours when the liposomes are suspended in 600 mM sucrose. These liposomes are useful in the treatment of cancer. In particular, HEPC:Chol:DSPE-PEG2000 (50:45:5) liposomes comprising BI 2536 and citrate:phosphate in a ratio of 1:3.