Targeted therapy drugs are a lot like Navy Seals behind enemy lines: stealth and clandestine operatives with different specialties. They create very strategic problems for their target: cancer. And they’re so good at it that they may be the next beachhead in the war on cancer.
First, cancer cell profiles are analyzed at the molecular level and, once a specific target can be identified, a drug is designed to make it malfunction. Some rewire the intricate network of signals that govern how the tumor communicates growth instructions. Blocking these signals can stop the disease progression and, in some cases, actually cause the cancer to self destruct.
I participated in a clinical trial of a monoclonal antibody drug that did exactly this. Its code name was APOMAB, which stood for Apoptosis (or cell suicide) and MAB for monoclonal antibodies (cloned antibodies of a single type). And, because it was engineered to affect cancer cells, it ignored healthy ones. It was nothing like chemo at all.
Many targeted therapies are available to cancer patients now, such as those targeting the cellular receptor for estrogen. Most Estrogen Receptor-positive (ER-positive) breast cancer tumors and some forms of ovarian cancer feed on estrogen. By binding a drug to the estrogen receptor, it blocks estrogen from binding to it. Tamoxifen is an example of this drug.
Aromastase inhibitors are another class of drugs targeted at estrogen - in this case, an enzyme that produces estrogen. Once blocked, the lower estrogen levels keep the cancer in check and retard the body’s ability to produce more tumors. This treatment is only useful for post-menopausal women because active ovaries can produce enough of the enzyme to override the treatment. Arimidex and Femara are two commonly used drugs of this type.
Another form of breast cancer, called HER-2 (Human Epidermal Growth Receptor 2) Positive, is treated with a monoclonal antibody drug that binds to the HER-2 receptor. This drug, named Herceptin, not only keeps the cancer from growing; it may cause the patient’s immune system to attack the cancer.
Other approved targeted therapies treat some forms of leukemia, gastrointestinal stromal tumors, squamous cell carcinoma, colorectal cancer, advanced renal cell carcinoma, non-small cell lung cancer, multiple myeloma, lymphoma and pancreatic cancer.
Some monoclonal antibodies interfere with cancer growth through a process known as angiogenesis, which cuts off the blood supply by blocking the growth of the tumor’s blood vessels. The drug Avastin is used to treat glioblastoma, non-small cell lung cancer, metastatic breast and colorectal cancers and some ovarian cancers.
Other targeted therapies strengthen the immune system, then cause the body to destroy the cancer as it would an infection. Others deliver toxic molecules directly into the cancer cells, poisoning them from the inside out. Some work in conjunction with traditional therapies and make them more effective; some replace them.
Of course there are issues with any drug. But the overall objective of targeted therapies is to save lives, treat only the disease, reduce toxicity of healthy cells, only treat patients who benefit from the drug, and help make cancer a manageable, survivable disease.
It’s been my strategy to not worry about a “cure.” My plan is to stay in the best condition possible -medically and mentally - until new treatments are available. And the time may have come. I’m actually on my third targeted therapy drug and I can’t wait to see what comes next.
For information, contact the National Cancer Institute at www.cancer.gov.