Abstract: Optical tweezers are a means to manipulate objects with light. Optical tweezers can obtain a nanometer space, piconewton force, and a millisecond resolution; thus, they are excellently suited for studying biological processes from the single-cell to the single-molecule level. Optical tweezers can screen and manipulate tumor cells, study single molecule, and monitor cancer treatments. Thus, optical tweezers will promote the progress of cancer research and treatments.