Single dose of drug trastuzumab is linked to substantial reduction in HER2-positive breast cancer tumor, accoring to a recent study. This type of breast cancer tests positive for the human epidermal growth factor receptor 2 (HER2) protein.

Case Western Reserve University researchers said the strong immune response inside the tumor can be measured after a single dose of the drug. The same immune activity was not observed in the participants given a single dose of another chemotherapy type.

The drug trastuzumab is commercially sold as Herceptin. Apart from the treatment of HER2-positive breast cancer, the drug is also used to treat metastasized cancer and adenocarcinoma.

Prior to mass removal, only half of HER2-positive patients have tumors responding completely to the drug. When trastuzumab is taken with pertuzumab or other HER2-targetting treatments, about 60 percent of the participants have a complete response. Because of this, the researchers stressed the need to identify the women who will benefit from this pre-surgical treatment.

"Our study showed, for the first time, that the immune-cell-activating properties of trastuzumab are likely related to the subtypes of breast cancer," said Vinay Varadan, Ph.D., an assistant professor at the University's School of Member. "Knowing this can inform future trials studying the usefulness of adding immunotherapy drugs to trastuzumab." 

Among all patients in the study, the women with HER2-enriched subtype of the breast cancer type showed the most significant immune response after taking a single dosage. This subtype is where the progesterone and estrogen receptors are negative.

Additionally, the researchers found that T-cell marker PD-1 expression increased in female patients with HER2-enriched type of the disease. This predictive ability was not seen in the tumors prior to any therapy.

"We found that higher Immune Index evaluated after just one dose of trastuzumab predicted the tumor's response," added Varadan.

This suggests that a single trastuzumab dose can help identify the patients who will benefit best from the trastuzumab-based treatments.

The research team said these new findings can help guide future clinical trials that will analyze the effectivity of combining trastuzumab with other immunotherapy drugs.

Additional research will analyze why some breast cancer types show strong immune response to the drug with anti-HER2 therapy while others do not react at all.

The study was published in the Clinical Cancer Research journal. 

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