Abiraterone Approval Extended to Treat Late-Stage Prostate Cancer
Men with castration-resistant prostate cancer that has spread can now be treated with abiraterone acetate (Zytiga) before receiving chemotherapy. The Food and Drug Administration (FDA) expanded the approved use of abiraterone on December 10.
The FDA initially approved abiraterone in April 2011 for use in patients whose prostate cancer had progressed after treatment with the chemotherapy docetaxel. Abiraterone is a pill that reduces testosterone production.
Testosterone stimulates the growth of prostate tumors, so drugs or surgery that reduce testosterone production or block testosterone’s effects are used to slow the growth of prostate cancer. However, most prostate cancers eventually become resistant to these treatments. These castration-resistant cancers continue to grow even when levels of testosterone are very low. Abiraterone is designed to treat these tumors by inhibiting the production of androgen in the testes, adrenal glands, and prostate cancer tumors themselves.
Abiraterone’s safety and effectiveness for its expanded use were established in a clinical study of 1,088 men with late-stage castration-resistant prostate cancer who had not previously been treated with chemotherapy. Participants received either abiraterone or a placebo (both in combination with the corticosteroid prednisone).
The study was designed to measure the length of time a patient lived before death (overall survival) and the length of time a patient lived without further tumor growth as assessed by imaging studies (radiographic progression-free survival, or rPFS).
Interim results from the study were published December 10 in the New England Journal of Medicine. According to an updated analysis cited in the FDA news release, patients who received abiraterone had a median overall survival of 35.3 months compared with 30.1 months for those receiving the placebo. The updated results, which have yet to be published, also showed abiraterone improved rPFS. The median rPFS was 8.3 months in the placebo group and had not yet been reached for patients treated with abiraterone at the time of analysis.
The most common side effects reported included fatigue, joint swelling or discomfort, swelling caused by fluid retention, hot flashes, diarrhea, vomiting, cough, high blood pressure, shortness of breath, urinary tract infection, and bruising.
The most common laboratory abnormalities included low red blood cell count; high levels of the enzyme alkaline phosphatase, which can be a sign of other serious medical problems; high levels of fatty acids, sugar, and liver enzymes in the blood; and low levels of lymphocytes, phosphorous, and potassium in the blood.
Cabozantinib Approved to Treat Rare Type of Thyroid Cancer
Medullary thyroid cancer is a rare type of thyroid cancer. The disease develops in cells in the thyroid gland that make a hormone called calcitonin, which helps maintain a healthy level of calcium in the blood. Cabozantinib is a kinase inhibitor that blocks abnormal kinase proteins involved in the development and growth of medullary cancer cells.
“Prior to today’s approval and the approval of [vandetanib] in April 2011, patients with this rare and difficult-to-treat disease had limited therapeutic treatment options,” Dr. Richard Pazdur, director of FDA’s Office of Hematology and Oncology Products, said in a news release.
The safety and effectiveness of cabozantinib were established in a clinical study that included 330 patients with medullary thyroid cancer. Patients treated with cabozantinib lived longer without the cancer progressing, and some experienced tumor shrinkage.
Patients who were given cabozantinib lived a median of 11.2 months without tumor growth compared with a median of 4 months for patients receiving a placebo. In 27 percent of patients treated with cabozantinib, tumors shrank, with the response lasting for a median of nearly 15 months, whereas none of the tumors shrank in patients who received a placebo. Treatment with cabozantinib did not extend patients’ lives.
The drug was approved with a boxed warning alerting patients and health care professionals that severe and fatal bleeding and perforations and fistulas in the colon occurred in some patients.
The most common side effects included diarrhea, inflammation or sores of the mouth, hand-foot syndrome, nausea, fatigue, new or worsening high blood pressure, and abdominal pain and constipation. The most common laboratory abnormalities included increases in liver enzymes, low calcium and phosphorus levels, and decreased white blood cells and platelets.