[gdpawel]

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 (Cancer 2003 Jun 15;97(12):2972-7).

The monoclonal antibodies like Herceptin 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 (in the same way that neighbors can share food).