Herceptin: Monoclonal Antibody for Breast Cancer Treatment
Herceptin (trastuzumab) was approved in 1998 for treating breast cancer
patients who did not respond to chemotherapy. Herceptin
was also approved as a first-line treatment for metastatic breast cancer
when used in conjunction with Taxol.
The Mechanism of Action
Herceptin is a monoclonal antibody that specifically
binds to HER2, a protein
which is found on the surface of some normal cells
and involved in regulating cell growth.
Herceptin is able to slow the most
aggressive form of metastatic breast cancer and yet without the severe
side effects of traditional chemotherapy owing to its specific antigen
Herceptin is derived from part of a mouse antibody bioengineered
to closely resemble a human antibody. In metastatic breast cancer,
approximately 30% of tumors produce excess amounts of HER2,
in which case, the cancer tends to be more aggressive.
Herceptin specifically targets cancer cells which over express HER2,
but is of no much benefit for those which do not.
Herceptin is the second monoclonal antibody approved to treat cancer.
The first one is Rituxan, which was approved in 1997
for treating patients with one type of non-Hodgkin's lymphoma.
More than 1.6 million women have been diagnosed with breast cancer
in the United States, and there are about
180,000 new cases diagnosed each year,
according to the American Cancer Society.
In a randomized controlled clinical trial,
the breast cancer patients who received chemotherapy
plus Herceptin had less rapid tumor growth with higher one-year survival rates.
In another clinical trial, Herceptin was found effective when
used alone for a group of breast cancer patients who had relapsed following
previous chemotherapy for metastatic disease.
In both clinical trials, the patients associated with
highest levels of HER2 protein responded best to Herceptin.
To identify patients who may benefit from Herceptin requires a test
of HER2 protein on the cancer tissue.
Patient selection is needed as the use
of Herceptin either alone or in combination with chemotherapy can result in a
weakening of the heart muscle and possibly lead to congestive heart failure.
This potentially life-threatening side-effect is most common in patients who
receive Herceptin in combination with chemotherapy consisting of
anthracyclines and cyclophosphamide (AC).
For this reason, Herceptin is not approved to be used with AC.
All patients treated with Herceptin should have their heart function assessed
before starting treatment and be closely monitored during treatment.
Physicians must exercise great caution for patients with heart problems.