Change in HER2 Status May Reduce Effectiveness of Trastuzumab

The study: The study, conducted at the University of Texas M.D. Anderson Cancer Center, included 143 women with HER2(human epidermal growth factor receptor 2)-positive tumors (determined before treatment began) who received chemotherapy and trastuzumab (Herceptin) before surgery. About 25% of breast tumors produce too much HER2, called HER2-positive cancer. A tumor with low levels of HER2 is called HER2-negative. Trastuzumab is a specific treatment for a HER2-positive tumor

The results: Of the 143 women, 50% had no sign of invasive cancer at the time of surgery. In other words, treatment with chemotherapy and trastuzumab was able to eliminate all signs of invasive cancer before surgery.. Among women who had signs of invasive cancer (meaning that treatment was not completely successful), tumor samples from before and after surgery were available for 23 of the women. These samples were tested for HER2. For about 30% of these women, the HER2 status of the tumor changed from HER2-positive to HER2-negative during treatment.

After approximately 10 months, the women who had signs of invasive cancer during surgery were 3 times more likely to have a recurrence (cancer that comes back after treatment) than those who did not. Two women (3%) who had no signs of invasive cancer had a recurrence compared with eight women (11%) who had signs of invasive cancer.

What this means for patients

This study suggests that the HER2 levels in a tumor can change, which could either mean that tumor cells change over time, or that some tumors are composed of both HER2 positive and HER2 negative tumor cells. “This information is important for doctors to keep in mind so we can provide patients with the most appropriate treatment for their cancer,” said lead author Elizabeth A. Mittendorf, MD, Assistant Professor in the Department of Surgical Oncology at the University of Texas M.D. Anderson Cancer Center.

What to Ask Your Doctor

• What is my HER2 status? What does this mean?
• What are my treatment options? Am I a candidate for HER2-specific treatment?
• What are my other treatment options, if this treatment stops being effective?