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19 April 2020

The US Food and Drug Administration (FDA) has recently approved a new treatment for patients with metastatic breast cancer. Tucatinib (Tukysa) was approved for use in combination with 2 other agents, trastuzumab (Herceptin) and capecitabine (Xeloda) in patients with unresectable (too advanced to remove with surgery) or metastatic (spread to other areas of the body, such as bone, liver, lungs or brain) Her2/neu over-expressed breast cancer (Her2+). Tucatinib is approved for patients who have already been treated with one or more anti-Her2/neu treatments.

Tucatinib is a an oral (pill) medication known as a tyrosine kinase inhibitor. Results of the Her2CLIMB trial were presented in December at the San Antonio Breast Cancer Symposium. The study enrolled 612 patients with metastatic or unresectable Her2+ breast cancer who had received at least one other Her2+ targeted agent but were experiencing progression of disease. Unique to this study was that almost half of the participants had metastases to the brain – often these patients are excluded from clinical trials.

Some of the key findings were that in patients who received tucatinib with trastuzuab and capecitabine versus those who received trastuzumab and capecitabine alone:

  • Median progression free survival was 7.8 months versus 5.6 moths
  • Median progression free survival for patients with baseline brain metastases was 7.6 versus 5.4 months
  • Median overall survival was 21.9 versus 17.4 months
  • Confirmed objective response rate was 40.6% versus 22.8%

Serious adverse reactions occurred in 26% of patients and 6% of patients had to stop treatment due to adverse reactions. The most common side effects were diarrhea, hand-foot syndrome, nausea, fatigue, liver toxicity, mouth sores, decreased appetite, abdominal pain, headache, anemia and rash.

The approval of tucatinib provides another option for patients with aggressive breast cancer, including those who have brain metastases. However, as previously discussed, this study is a reminder of how far we have to go to achieve a reliable and long-lasting treatment response in patients with metastatic breast cancer.

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