Vinorelbine (VNR) is a new vinca alkaloid derivative semi-synthesized by Potier et al. The antitumor activity of VNR was superior to other vinca alkaloid antitumor agents, and the neuro-toxicity of VNR was weaker than those of other vinca alkaloids. In nude mice xenografted human tumor models, VNR showed antitumor activity against eight of eleven tumor models (non-small cell lung cancer: 4/4, breast cancer: 2/3, colon cancer: 0/2, stomach cancer: 2/2). Especially, VNR showed tumor-regressive activity against LC-6 non-small cell lung cancer and MX-1 breast cancer. The antitumor activity of VNR against non-small cell lung cancer was superior to that of vindesine (VDS), which had been one of the key drugs of non-small cell lung cancer in the clinic. In combination chemotherapy, VNR plus cisplatin (CDDP) was better than VDS plus CDDP, which had been one of the standard regimens of non-small cell lung cancer chemotherapy. The potent antitumor effect of VNR with minor neurotoxicity was explained by VNR having stronger activity on mitotic microtubules than axonal microtubules. It was supposed that less activity of VNR against mitotic microtubules would be related to different composition of microtubule-associated TAU isoforms in the two types of microtubules. In non-small cell lung cancer, VNR resulted in a significantly higher response rate than VDS. In combination with CDDP, VNR resulted in longer survival than VDS with a significant log-rank test. In advanced breast cancer, VNR resulted in a high response rate in 1st line and 2nd line treatment. VNR is effective in combination with chemotherapeutic agents such as anthracycline, fluorouracil and Taxol. In Japan, the clinical trial in breast cancer is now ongoing.