Herceptin causes flu-like symptoms in about 40% of the people who take it. These symptoms may include:
- muscle aches
Side effects generally become less severe after the first treatment. Your treatment team will monitor you during your infusions, especially your first dose, and can adjust the infusion if you are very uncomfortable. If you are receiving Herceptin every 3 weeks, you may have stronger side effects.
If you are receiving Herceptin with chemotherapy, you may also experience chemotherapy side effects.
Serious heart side effects
Less commonly, Herceptin can damage the heart and its ability to pump blood effectively. This risk has ranged between 5% to 30%. The damage can be mild and result in either no symptoms or signs of mild heart failure, like shortness of breath. Less commonly, the heart damage is bad enough that people experience life-threatening congestive heart failure or a stroke. The risk of heart damage, especially severe damage, is greater when Herceptin is given along with other chemotherapy medicines known to cause heart damage. Adriamycin is an example of a chemotherapy that can cause heart damage.
Women who experience mild or more serious heart damage can stop taking Herceptin and start taking heart-strengthening medications. This often brings heart function back to normal.
Testing your heart before and during Herceptin treatment
Before starting Herceptin therapy, you should have an echocardiogram or a MUGA (multigated blood-pool imaging) scan to check how well your heart is functioning.
- An echocardiogram uses sound waves to take detailed pictures of the heart as it pumps blood. For this quick test, you lie still for a few minutes while a device that gives off sound waves is briefly placed on your ribs, over your heart. There is no radiation exposure with this test.
- A MUGA scan takes about an hour. In this test, a tiny amount of radioactive material is injected into a vein in your arm. This material temporarily hooks onto your red blood cells. You lie still while a special camera that can detect the radioactive material takes pictures of the blood flow through your heart as it beats.
When you first start taking Herceptin, your doctor might want you to have MUGA scans or echocardiograms every few months to detect any sign of heart failure. But after you've been on Herceptin for a while, you may need a heart-monitoring test only every 6 months or so. This is because heart failure is less likely to occur the longer you take Herceptin.
Notify your doctor immediately or go to the nearest emergency room if you're taking Herceptin and you develop any symptoms of heart failure, such as shortness of breath, difficulty breathing, a fast or irregular heartbeat, increased cough, and swelling of the feet or lower legs.
Serious lung side effects
Herceptin can rarely cause two possibly related serious reactions that interfere with breathing. One of these is a reaction during or shortly after Herceptin is being administered. This is like a bad allergic reaction, with symptoms that include hives, as well as wheezing and trouble breathing due to sudden swelling and narrowing of the airways. The other reaction, called pulmonary toxicity, results in swelling of the lung tissue, low blood pressure, and possibly fluid buildup around the lungs (called pleural effusions).
The risk of these life-threatening reactions is rare -- much less than 1%. In most cases, these reactions happen during infusion or within the first 24 hours of the first dose of Herceptin. Less commonly they can happen within a week of the first dose. Only occasionally do these reactions occur with the second or later doses. The lung reaction can be more severe when lung disease, such as asthma or emphysema, already exists, or if the breast cancer has spread significantly into your lungs. If you are currently undergoing treatment with Herceptin and have been tolerating it well, you're unlikely to develop these serious reactions.
Even though the severe side effects are relatively rare, your doctor should check you carefully for any heart or lung problems before starting to treat you with Herceptin. You should also be monitored closely for these serious side effects during treatment.