Tumors are heterogeneous structures that contain different cell populations. Laser capture microdissection (LCM) can be used to obtain pure cancer cells from fresh-frozen cancer tissue and the surrounded environment, thus providing an accurate snapshot of the tumor and its microenvironment in vivo. We describe a new approach to isolate pure cancer cell population and evaluate protein expression. The process includes immunocytochemistry, laser microdissection, and western blot analysis. Using this technique, we can detect proteins such as X-linked inhibitor of apoptosis protein (XIAP) and Fas ligand (FasL) with as little as 1000 cells.