In a recent phase 2 trial, the addition of iniparib to gemcitabine and carboplatin significantly increased clinical benefit and survival—but not toxic effects—in a small group of women with metastatic triple-negative breast cancer.
Metastatic triple-negative breast cancer is estrogen-receptor (ER)-negative and progesterone-receptor (PR)-negative, and has no overexpression of human epidermal growth factor receptor type 2 (HER2). Compared with hormone-receptor-positive subtypes of breast cancer, this aggressive subtype is characterized by higher rates of visceral and central nervous system metastases and poorer disease-specific survival, leaving patients with a very poor prognosis and a median survival of approximately 1 year.
The anticancer agent iniparib is a poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor; PARP is a therapeutic target for triple-negative breast cancer. In the study of metastatic triple-negative breast cancer patients, 116 participants underwent chemotherapy with gemcitabine and carboplatin, but 57 of those women also received iniparib. The addition of this agent improved rate of clinical benefit from 34% to 56%, improved rate of overall response from 32% to 52%, prolonged the median progression-free survival from 3.6 months to 5.9 months, and prolonged the median overall survival from 7.7 months to 12.3 months. The two groups of patients experienced similar rates of adverse events, with the most frequent grade 3 or 4 adverse events being neutropenia, thrombocytopenia, anemia, fatigue or asthenia, leucopenia, and increased alanine aminotransferase level.
As investigator Joyce O’Shaughnessy, MD, of Baylor Charles A. Sammons Cancer Center (Dallas, Texas) and colleagues note in their online report for The New England Journal of Medicine (www.nejm.org/doi/pdf/10.1056/NEJMoa1011418), a larger phase 3 trial is under way to better evaluate overall and progression-free survival.