Nothing to do with cancer.

A very rigid cavity molecule that have small openings for small guests. Since the inside of this molecular cage is shielded from the solvent, it is even possible to carry out reactions inside. This is especialy useful if the reactants are unstable, and can be stabilised by the microenvironment. An example of this sort of reaction is:

  O=C1C=CC=CO1  -> (light) ->   C1=CC=C1
 (alpha-pyrone)      ->      (cyclobutadiene)