In 2012 a trial found that the new cancer drug Halaven (eribulin mesylate)performed as well as Xeloda (capecitabine), but not significantly better for metastatic breast cancer patients. So why would doctors prescribe an expensive new drug rather than a well-established one with which they had experience? A new study offers details about when Halaven might be superior to older drugs.
Breast cancer is actually about ten different diseases. About 80% of cases are invasive ductal carcinoma (IDC), meaning the cancer cells started in the milk ducts of the breast. However, one in five breast cancer patients will have one of the less common forms of the disease.
To make matters more complicated, scientists now know that even within a type of breast cancer, each tumor will have defining characteristics that affect the treatment the patient should receive. A woman with an estrogen or progesterone receptor positive tumor, will probably have a hormonal drug like Tamoxifen or an aromatase inhibitor as a follow-up treatment. If a tumor is positive for Her2, Herceptin or another targeted therapy may be effective against it. You might want to think of these characteristics as the hair and eye color of your tumor. They help identify it and give your doctor better information about how to treat your cancer.
They also complicate studies about how effective a drug is. Now trials need to look at the effects of a drug not just on tumors in general, but on each subgroup. A 2013 study analyzing the results of 1,102 patients who received either Halaven or Xeloda found that certain subgroups benefited more from Halaven.
Patients with HER2-negative disease who received Halaven rather than Xeloda had an overall survival of 15.9 months versus 13.5 months. ER-negative disease patients lived 14.4 months versus 10.5 months. A difference of three or four months doesn’t sound like much, but keep in mind that these are averages for Stage IV patients whose life expectancy was limited, and some of them would do significantly better than the average.
Halaven seemed to work best on triple negative tumors--14.4 months versus 9.4 months overall survival. This is hopeful news for triple negative patients whose tumors tend to be more aggressive and who have fewer treatment options.
The researchers also compared quality of life on the two drugs. Stage IV patients generally can expect to be in treatment for the rest of their lives, so quality of life issues are very important to them as they discuss a drug with their doctors. Some women are to the point that they would rather stop treatment than use a drug that would make them feel miserable while giving them only a few months more.
The patients receiving Halaven reported fewer problems with cognitive functioning, and they had less nausea and diarrhea. The most severe side effects were lowered white blood cell count and peripheral neuropathy (nerve damage), but these side effects are common with other drugs too. In the original study for Halaven’s approval, 57% of the patients had a significantly lowered white blood count, and for 12%, this lowered count lasted longer than a week. In that same trial, 22% of patients reported problems with neuropathy. In fact, neuropathy was the main reason patients decided to discontinue the drug. Still compared to other drugs, Halaven may be more tolerable for many patients.