Targeted therapies act on specific molecular targets that are associated with cancer. Most standard chemotherapies act on all rapidly dividing normal and cancerous cells. They are designed to interact with their target, whereas many standard chemotherapies are designed to kill cells.
Targeted therapies are often cytostatic, meaning that they block tumor cell growth. In comparison, standard chemotherapies are cytotoxic meaning that they kill tumor cells.
One approach to identify potential targets is to compare the amounts of individual proteins in cancer cells with those in normal cells. Proteins that are present in cancer cells, but not normal cells or that are more abundant in cancer cells, would be potential targets, especially if they are known to be involved in cell growth or survival.
An example is the human epidermal growth factor receptor 2 protein (HER-2) found in HER2 Positive Breast Cancer. HER-2 is expressed at high levels on the surface of some cancer cells. Targeted therapies known as CD4K and CDK6 block proteins in hormone receptor-positive breast cancer cells, which helps stop the cells from dividing. This can slow cancer growth.
Another approach to identify potential targets is to determine whether cancer cells produce mutant / altered proteins that drive cancer progression. Abnormalities in chromosomes that are present in cancer cells, but not in normal cells, sometimes result in the creation of a fusion gene (a gene that incorporates parts of two different genes) whose product, is called a fusion protein. It is believed that this may drive cancer development. Genetic tests detect mutations or changes in the DNA of cancer cells.
What types of biologic/targeted therapies are available?
Thanks to endless hours of research and patients who have participated in clinical trials, we have several types of these therapies to use in our arsenal in the fight against cancer. They include:
slow or stop the growth of hormone-sensitive tumors.
Signal transduction inhibitors:
block the activities of molecules that participate in signal transduction, the process by which a cell responds to signals from its environment.
Gene expression modulators:
modify the function of proteins that play a role in controlling gene expression.
block the growth of new blood vessels to tumors necessary for tumors to grow.
cause cancer cells to undergo a process of controlled cell death called apoptosis.
work by triggering or stimulating a person’s immune system to destroy cancer cells.
that deliver toxic molecules can cause the death of cancer cells specifically. Once the antibody has bound to its target cell, the toxic molecule that is linked to the antibody—such as a radioactive substance or a poisonous chemical—is taken up by the cell, ultimately killing that cell.
Cancer vaccines and gene therapy:
are sometimes considered targeted therapies because they interfere with the growth of specific cancer cells.
Are there limitations to what these therapies can do?
Biologic/targeted therapies do have some limitations. Cancer cells can become resistant to the therapy. Either the target itself can change or mutate, so that the targeted therapy no longer interacts well with it. The other thing that can happen is that the tumor will find a new way to achieve tumor growth that does not depend on the target.
Is a biologic or targeted therapy ever used at the same time as chemotherapy?
Depending on the cancer, sometimes a person may receive both treatments simultaneously.
Are there side effects from receiving a biologic/targeted cancer therapy?
Originally, it was expected that targeted cancer therapies would be less toxic than traditional chemotherapy drugs because cancer cells are more dependent on the targets than are normal cells. Like every patient though, the side effects vary depending on the patient’s health, type of cancer and treatment that is used.