What distinguishes cancer cells from the cells of benign neoplasms?

Pathology: Cancer cells can be viewed microscopically. It is the characteristics of this parrafin embedded material that provide information about the aggressive nature of the cells. Cancer cells are characterized by the presence of high cell #, high mitotic #, bizarre pleomorphic shapes, and local invasiveness.Also there is frequently the increase in vascularity with new blood vessels "feeding" the cancer.

Disordered growth: Benign tumors grow locally and do not spread. Under the microscope, the cells look like the gland they are from and they are not invading. Cancer cells have disordered growth, frequently do not look like the originating gland and show invasion.

Genome destabilized: The key to cancer is that enough mutations have accumulated to render the genome itself unstable. Eventually a clone will acquire the ability to invade and spread. We can pick this up using molecular biology techniques. They also look different, but it takes a pathologist several years to learn to tell all the subtleties.