The pathway from normal cell to cancerous cell is complex

The "gas pedal" and "brake" analogies we have been using for oncogenes and tumor suppressor genes, respectively, are elegant but simplified. There are many oncogenes and tumor suppressor genes, some of which act only in certain cells at certain times. Therefore, a complex sequence of events must occur before a normal cell becomes malignant.

Because colon cancer progresses to full malignancy slowly, it is possible to describe the oncogene and tumor suppressor gene mutations at each stage in great molecular detail. Figure 17.18 outlines the progress of this form of cancer. At least three tumor suppressor genes and one oncogene must be mutated in sequence for an epithelial cell in the colon to be-

Some tumor suppressor genes code for cell adhesion/recognition proteins.

In cancer, mutations of these genes cause cells to lose adhesion to their neighbors and spread.

Some tumor suppressor genes code for cell adhesion/recognition proteins.

In cancer, mutations of these genes cause cells to lose adhesion to their neighbors and spread.

Tumor Suppressor Pathway
17.17 Tumor Suppressor Gene Products Inhibit Cell Division and Cancer Mutations can affect any of the several ways in which tumor suppressor genes inhibit cell division, allowing cells to divide and form a tumor.
Section through colon (large intestine)

Normal cells

Loss of normal tumor suppressor gene APC

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