Experimental Iniparib Increases Survival Only Slightly in Metastatic Triple-Negative Disease

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Iniparib is an experimental PARP inhibitor. A few small, early research studies have shown that some advanced-stage breast cancers -- including triple-negative breast cancers -- that have stopped responding to standard treatments will respond to a combination of chemotherapy and a PARP inhibitor.

A study found that adding iniparib to a combination of Gemzar (chemical name: gemcitabine) and Paraplatin (chemical name: carboplatin) increased overall survival by almost 5 months in women diagnosed with metastatic triple-negative breast cancer compared to women who got only Gemzar and Paraplatin. Overall survival is how long the women lived with or without the cancer growing.

Still, the difference in survival between women who did and women who didn't get iniparib wasn't statistically significant. This means that the increase in survival could have been due to chance and not because of the iniparib.

Metastatic breast cancer is cancer that has spread to other parts of the body away from the breast, such as the bones or liver.

Triple-negative breast cancer is:

  • estrogen-receptor-negative
  • progesterone-receptor-negative
  • HER2-negative

Overall, about 15% to 20% of breast cancers are triple-negative. Triple-negative cancers are usually more aggressive, harder to treat, and more likely to come back (recur) than cancers that are hormone-receptor-positive and/or HER2-positive. Hormonal therapy and the targeted therapies Herceptin (chemical name: trastuzumab) and Tykerb (chemical name: lapatinib) usually don't work on triple-negative breast cancer.

The PARP (poly ADP-ribose polymerase) enzyme fixes DNA damage in cells, including DNA damage caused by chemotherapy medicines. Scientists developed PARP inhibitors based on the idea that a medicine that interferes with or inhibits the PARP enzyme might make it harder for cancer cells to fix damaged DNA. This would make the cancer more likely to respond to chemotherapy and less likely to become resistant to chemotherapy.

While these results are disappointing, researchers are continuing to study how PARP inhibitors might be used to treat breast cancer.

If you're being treated for advanced-stage breast cancer, you and your doctor may be considering a number of options, especially if the cancer is triple-negative and/or has stopped responding to standard treatments. Treatment with an experimental regimen that includes a PARP inhibitor such as iniparib may be an option if you're willing to participate in a clinical trial. Ask your doctor if there are any clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages for more information.

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