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Posted March 31, 2012: by Knowledge of Health
News reports herald a possible future cure for cancer, a cure that appears so convincing in the animal laboratory that it tempts many to think a true cancer cure may soon be at hand. But careful examination suggests what is clearly a cure in the animal lab may not be a practical cure in the oncology clinic.
In recent times there has been a renaissance in immunotherapy for cancer. Immunotherapy aims to activate an efficient immune response against tumors or prevent cancers from occurring in the first place. Decades ago cancer researchers dismissed this approach in favor of the toxic cancer cell-killing treatments that now predominate. But now cancer researchers are reporting some breakthroughs, at least in the animal laboratory.
Normal healthy cells carry proteins on their surfaces that mark them as “self” and keeps them from being attacked by the immune system. White blood cells then easily recognize invading germs or tumor cells and either destroy them outright with a burst of free radicals issued from white blood cells known as neutrophils or swallow them entirely by white blood cells known as macrophages. But tumor cells also exhibit these “self” proteins on their surface to escape immune surveillance.
If these proteins can somehow be negated then the immune system would have a chance to attack and kill off cancer cells. Specifically, roaming white blood cells known as macrophages recognize a protein called CD47 and therefore do not attack and engulf cancer cells. In this manner cancer cells escape the normal immune surveillance that keeps cancer cells at bay.
Cancer cells typically have a higher level of CD47 than healthy cells and the amount of CD47 predicts the survival of cancer patients.
Cancer researchers have recently documented the blockade of the CD47 cell-surface receptor with a monoclonal antibody to re-activate macrophages to engulf cancer cells and kill them. Since virtually all known types of tumor cells exhibit the CD47 receptor on their surface, this development may be monumental.
This single monoclonal antibody drug has now been demonstrated to shrink or even cure human breast, ovary, colon, bladder, brain, liver, and prostate tumors that have been transplanted into laboratory mice.
In recent years blockade of the CD47 receptor had been shown to cure some cases of non-solid tumors (lymphomas and leukemias) in the research lab.
It is important at this juncture in time to look forward in time to see how it may alter current cancer treatment.
So far monoclonal antibodies aren’t receiving rave reviews by cancer researchers. One recent report says “side effects, elevated costs and resistance problems” limit the efficiency of monoclonal antibodies as targeted therapy against cancer.
Use of monoclonal antibodies that block the formation of new blood vessels that feed tumor cells, a process called angiogenesis, has been modestly successful in prolonging survival for colorectal cancer.
So where is oncology headed here in its quest to conquer cancer via the use of monoclonal antibodies to re-arm the immune system against tumor cells?
We can get a picture of what monoclonal antibody therapy for cancer would be like by studying another human disease that is successfully treated using this approach.
Monoclonal antibodies are also used quite successfully to inhibit abnormal new blood vessels that invade the visual center of the eye in a disease called wet macular degeneration. Aged eyes that are deprived of oxygen deliver due to poor circulation will trigger a signal to produce new blood vessels to deliver more oxygen, but this can permanently destroy vision. The injection of a monoclonal antibody that blocks a gene known as vascular endothelial growth factor (VEGF) causes these abnormal blood vessels to recede and vision to be restored.
However, anti-VEGF therapy requires repeated treatments, about every six weeks, about 6 to 8 treatments a year.
So imagine now that oncologists could possibly be treating tumors that can be directly reached with a needle with repeated injections of monoclonal antibodies that block CD47. Remote tumors in the brain and deep internal organs may not be accessible to this treatment and it is anticipated the cost of a single treatment would be expensive. The cost of repeated treatments would likely soar beyond imagination.
Using 2005 data, there are about 1.37 million new cases of cancer diagnosed annually that are added to the pool of about 11 million Americans who have a history of cancer. Direct costs to provide cancer care runs close to $40 billion a year, without monoclonal antibody treatment.
To hazard a rough guesstimation, let’s say monoclonal antibodies targeted at the CD47 protein are injected in 1 million patients a year, six times a year at the cost of $3000 per injection, which includes fees for the physician and the outpatient center. We are talking about $18 billion of treatment that would likely be added to existing therapy, such as chemotherapy.
What if monoclonal antibodies did saves lives and produce temporary remissions, but not long-term cures? What if it did produce long-term cures but the patients would be subject to long-term invasive treatment? Current chemotherapy drugs are approved by the FDA if they shrink tumors by 50%, however none of them produce a cure and they only modestly prolong survival. © 2012 Bill Sardi, Knowledge of Health, Inc.
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