Adding Iniparib to Second, Third Chemo Regimen May Help Treat Metastatic, Triple-Negative Disease

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The targeted therapy iniparib is one of several experimental PARP inhibitors. 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 susceptible to chemotherapy and make it harder for cancer to become resistant to chemotherapy.

A new analysis of results from the BSI-201 trial suggests that women diagnosed with triple-negative metastatic breast cancer that was previously treated benefited from adding iniparib to the second or third chemotherapy regimen. Still, adding iniparib to the first chemotherapy regimen (called the first-line regimen) used to treat metastatic breast cancer offered no benefit.

The results were presented at the September 2011 European Multidisciplinary Cancer Conference (ECCO-ESMO).

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.

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

An earlier, smaller study suggested that iniparib combined with chemotherapy might benefit women diagnosed with metastatic, triple-negative breast cancer.

In the larger BSI-201 trial, 519 women diagnosed with metastatic, triple-negative breast cancer had received zero, one, or two previous treatment regimens for metastatic breast cancer. For more than half the women, the treatment given in the BSI-201 trial was the first treatment for metastatic breast cancer.

All the women were treated with the chemotherapy medicines Gemzar (chemical name: gemcitabine) and Paraplatin (chemical name: carboplatin). This combination is sometimes called GC. Half the women were randomly assigned to get iniparib with the chemotherapy regimen; the other half got a placebo (sugar solution) with the chemotherapy regimen.

Gemzar destroys cancer cells by acting as false building blocks in the cells' genes, causing the cells to die as they get ready to divide. Paraplatin weakens or destroys cancer cells by damaging the genetic material in the cells and making it hard for cells to repair any genetic damage. Gemzar, Paraplatin, and iniparib are all given intravenously.

Overall, the women who got iniparib along with the chemotherapy regimen did the same as women who got only the chemotherapy regimen.

But when the outcomes of women who were getting their first treatment for metastatic cancer in the study were compared to the outcomes of women who had been previously treated for metastatic cancer, the researchers found that adding iniparib to chemotherapy improved outcomes a bit in women who were getting the regimen as a second or third treatment. Compared to women who didn't get iniparib with a second or third chemotherapy regimen, women who did:

  • lived longer without the cancer growing (progression-free survival)
  • lived longer whether or not the cancer grew (overall survival)

The women who got iniparib with chemotherapy didn't have any more side effects than the women who got only chemotherapy.

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 still 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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