Pertuzumab, a member of a new class of agents that block HER2 epidermal growth factor receptors, shows promise in prolonging the lives of patients with recurrent prostate cancer, according to an article in the February 20 issue of Journal of Clinical Oncology.

The current study involved 41 US patients with treatment-resistant prostate cancer who had experienced disease progression after prior chemotherapy. Patients received the drug every three weeks until disease progression developed. Magnetic resonance (MRI) and computed tomography (CT) scans were used to evaluate tumors during drug therapy.

Although no patient had shrinkage of tumor, retrospective analysis showed that survival was prolonged to 16.4 months with the drug compared with a median of 10.7 months in a historical control group with similar baseline prognostic features.

“Advanced prostate cancer is difficult to treat - and the drug therapies currently available to these patients have not been very effective, especially in patients whose disease has progressed after chemotherapy treatment,” said David B. Agus, MD, principal investigator of the study and research director of Cedars-Sinai’s Louis Warschaw Prostate Cancer Center at the Samuel Oschin Comprehensive Cancer Institute.

“Pertuzumab may offer a new treatment approach for these patients when it is evaluated as a tool to slow - not stop or shrink -- tumor growth.”

“The theory is that by significantly slowing progression of the cancer, patients will experience a good quality of life for a longer period of time,” said Agus. “Ultimately, we hope drugs like pertuzumab will help us reach the point where cancer can be viewed as a lifetime disease to be managed much like AIDS is looked at now. This would be major shift from the current paradigm for cancer treatment, and is a promising area of research. This study must be viewed cautiously, however, as we are comparing statistics from historical control groups.”

Pertuzumab is a single-agent antibody designed to bind to the HER2 receptor and inhibit the ability of HER2 to pair with other HER family members (HER1, HER2, HER3 and HER4). If the pairing process (called dimerization) is not interrupted, the binding of these growth factors activates an intracellular signaling pathway that leads to tumor proliferation.

In the current study, the pertuzumab was well-tolerated, but no decline in prostate-specific antigen levels was detected during the study. According to the researchers, this study raises a question long debated in prostate cancer literature: What should clinical outcome standards or end point be for studies involving patients with advanced, intractable prostate cancer who have limited treatment options?

Randomized prospective trials will follow.