CLEVELAND, Feb. 29 (UPI) -- A single dose of the drug trastuzumab initiated a stronger immune response in one subtype of HER2-positive breast cancer tumors, according to a study.
Researchers at Case Western University report the immune response could be measured after the first dose by measuring the immune activity within tumor tissue.
Immune activity was not seen in HER2-positive patients given a single dose of another chemotherapy, suggesting the immune response to the drug is specific to both the substance and the tumor.
Trastuzumab, sold as Herceptin, is used to treat HER2-positive breast cancer, as well as adenocarcinoma and metastasized cancer, according to the National Cancer Institute.
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About half of women with HER2-positive cancer will see their tumors respond completely to trastuzumab before surgery, and 60 percent will have a complete response when trastuzumab is combined with other treatments.
Women with an HER2-enriched subtype of HER2-positive breast cancer -- a subtype that is estrogen and progesterone receptor negative -- were found to have the highest rate of immune response, observed after a single dose.
The study to determine the drug's immune-activating response was based on previous research showing the immune system can determine a tumor's response to treatment, leading to the clinical trials examining how the immune system interacts with the drug.
"Our study showed, for the first time, that the immune-cell–activating properties of trastuzumab are likely related to the subtypes of breast cancer," Dr. Vinny Varadan, an assistant professor at Case Western Reserve University School of Medicine, said in a press release. "Knowing this can inform future trials studying the usefulness of adding immunotherapy drugs to trastuzumab."
The study was published in the journal Clinical Cancer Research.
The researchers also found signatures of T-cell activity could be used to predict the immune system's response to the drug based on increased expression of PD-1, a marker of T-cells.
"The predictive ability of the Immune Index test was not observed in patient tumors before any therapy was given, suggesting that just a single dose exposure may be a beneficial way to identify which patients are most likely to benefit from trastuzumab-based chemotherapy and, thus, do not need additional anti-HER2 treatment," Varadan said.
Future research will focus on why some breast cancers have a strong immune response when treated with anti-HER2 therapy and others have no reaction.
