New cytotoxic drugs and targets in oncology.

New agents in the preclinical and early clinical pipeline (phases I and II) are described and some of the problems associated with their development are reviewed. The article focuses on tubulin poisons such as taxol, topoisomerase inhibitors, such as topotecan, and drugs such as bryostatin 1 and miltefosin, which interfere with specific signal transduction pathways involved in malignant cell growth.