[Tyrosine kinase inhibitors--solid cancers]

Tyrosine kinase inhibitors have drawn the most attention in recent years as molecular target agents for cancer treatment. The reason for this can only be the dramatic antitumor effects shown in early clinical trials against small cell cancer and chronic myeloid leukemia by the EGFR tyrosine kinase inhibitor, ZD1839, and the BCR-Abl tyrosine kinase inhibitor, STI-571, respectively. Various hypotheses were advanced in the preliminary stages of the clinical development of such molecular target agents: "They only prevent cancer cell proliferation and have no killer cell activity; they are extremely weak, and can not be expected to reduce tumors at the clinical level. "Or:" A long time is required before their physiological activity will be expressed in an antitumor effect." However, with non-small cell lung cancer, the most difficult tumor among solid cancers for an anticancer agent to be effective, not only was ZD1839 effective, but showed clear effectiveness in combination chemotherapy in the pretreatment stage. Moreover, the time for the expression of its tumor reduction effect was virtually the same as with conventional anticancer drugs, and its effectiveness proved to last longer after its initial expression. ZD1839 has succeeded in remaking the very image of molecular target agents for cancer treatment. In what follows, we focus mainly on the EGFR tyrosine kinase inhibitor, ZD1839.