A number of issues on the subject of Herceptin
There are a number of issues on the subject of Herceptin. In addition to taking this drug for a long time, these kind of individual, targeted oral drugs would be taken in addition to an existing repertoire of chemotherapy mixtures a cancer patient is already taking, instead of taking them alone. Adding even more potential toxicities and thousands of dollars to treatment.
Overt congestive heart failure is a very late and serious manifestation of heart muscle damage. For every patient with frank congestive heart failure, there is probably another two, three, four or five patients with heart muscle damage short of congestive heart failure. The sort of heart muscle damage which can cause fatigue and/or shortness of breath with moderate or mild exertion, which otherwise wouldn't occur.
We don't know what will happen 10 or 20 years from now in women who didn't need any adjuvant therapy at all, who would have been cured by surgery alone. Only a minority of patients who receive adjuvant therapy benefit from it. Adjuvant therapy is worth it if the women have to suffer only short term, temporary toxicity, and if it even slightly reduces the probability that their cancers will come back. But if it produces permanent toxicity, whether "chemo brain" or "heart muscle damage," that is a whole different order of magnitude in terms of risk.
Aside from the issue of congestive heart failure, past studies have suggested a potentially very serious weakness in the drug, the problem with central nervous system (CNS) metastasis. A study from the Dana Farber Cancer Institute identified central nervous system (CNS) metastases in women who receive trastuzumab-based (Herceptin) therapy for metastatic breast carcinoma. Central nervous system disease is defined as one or more brain metastases or leptomeningeal carcinomatosis (carcinomatous meningitis).
Central nervous system metastases was identified in 34% of patients at a median of 16 months after diagnosis of metastatic breast cancer and 6 months from the beginning of Herceptin treatment. Patients receiving Herceptin as first-line therapy for metastatic disease frequently developd brain metastases while responding to or stable on Herceptin. The authors of the study say that efforts to characterize other risk factors for development of CNS disease, optimal screening algorithms, and new treatment strategies may be warranted.
The potential benefits and risks of Herceptin have renewed concerns about the reliability of HER2 testing. Some studies have shown that the test produces false positives as often as 26% of the time, and may also carry some risk of false negatives. Herceptin also doesn't offer any benefit to women with HER2-negative cancer.
Lastly, monoclonal antibodies like Herceptin (and Erbitux) are "large" molecules. These very large molecules don't have a convenient way of getting access to the large majority of cells. Plus, there is multicellular resistance, the drugs affecting only the cells on the outside may not kill these cells if they are in contact with cells on the inside, which are protected from the drug. The cells may pass small molecules back and forth.
Exciting results have come from studies of multitargeted tyrosine kinase inhibitors,"small" molecules that act on multiple receptors in the cancerous cells, like Tyberb and Sutent. Targeted "small-molecule" therapies ruled at last years annual ASCO meeting of oncologists. The trend is away from the monoclonals to the small molecules, a trend in which a new predictive test may be able to hasten (The EGFRx Assay).
(Cancer 2003 Jun 15;97(12):2972-7)