1. A method for determining a response to administration of a chemotherapeutic or chemopreventive agent to an individual, comprising: (a) collecting a first tissue or cell sample from the individual before exposing the individual to the chemotherapeutic or chemopreventive agent; (b) collecting a second tissue or cell sample from the individual after exposing the individual to the chemotherapeutic or chemopreventive agent; (c) immunohistochemically staining the first and second tissue or cell samples using a detectably-labeled antibody directed against a biological marker associated with senescence, apoptosis or terminal differentiation; (d) measuring the optical density of the stained cells as in step (c), wherein the stained cells are illuminated with light having a wavelength absorbed by the stain; (e) determining whether expression of the biological marker associated with senescence, apoptosis or terminal differentiation was increased following exposure to the chemotherapeutic or chemopreventive agent.