The purpose of this study is to find the highest dose of the investigational drug SC16LD6.5 that can be given safely to patients with small cell lung cancer that has come back after treatment, and to evaluate the effectiveness of this treatment in these patients. SC16LD6.5 is an “antibody-drug conjugate.” This means it contains an antibody (a protein which binds to a specific site on cells) and an anticancer drug.
In the case of SC16LD6.5, the antibody binds to a specific protein on the surface of small cell lung cancer cells. Then it releases the anticancer drug to kill the cancer cell. SC16LD6.5 is given intravenously (by vein).