New research published in the Science Translational Medicine journal shows that breast cancer patients who had chemotherapy before receiving a surgery to treat their tumors may increase their risk of incurable metastatic cancer.

Women diagnosed with more advanced breast cancer are often recommended to receive chemotherapy to reduce the size of their tumor in order to have a lumpectomy surgery instead of a mastectomy.

While initially chemotherapy before surgery was used to treat large tumors, in recent years, this therapy has been used on women with smaller tumors as well, according to STAT News. Since less women are diagnosed with late-stage breast cancer, women in earlier stages have been given chemotherapy prior to surgery in hopes of extending lifespan.

However, this new research shows that chemotherapy before surgery may spread remaining tumor cells to spread to more distant areas and metastasize. The researchers uncovered this information by looking at human tissue and mice experiments.

The researchers discovered that the chemotherapy drugs paclitaxel, doxorubicin, and cyclophosphamide impact the “on-ramps” of the body, which leads toward metastasis. The “on-ramps” are areas on blood vessels that attract immune cells. If the immune cells mix with tumor cells, the blood vessel can initiate metastasis.

The researchers looked at lab mice with genetic mutations that make them more likely to develop breast cancer. They found that when more immune cells are present in the mouse body, the tumor cells became more mobile.

Regarding these findings, Julio Aguirre-Ghiso, of Mount Sinai School of Medicine, an expert in metastasis not involved in the study said, “It raises awareness that we might have to be smarter about how we use chemotherapy.”

Luckily, new guidelines from the American Society of Clinical Oncology (ASCO) may show that there are certain women who would not benefit from chemotherapy. This may reduce the likelihood that a woman ends up with metastatic breast cancer after receiving chemotherapy before their operation.

The American Society of Clinical Oncology updated their 2016 clinical practice guideline about using biomarkers in invasive early-stage breast cancer, according to Medscape. The organization recommends doctors to use the  the MammaPrint (Agendia) genomic test to determine if their patient would benefit from adjuvant chemotherapy. The test allows doctors to determine which patients can skip chemotherapy.

The Journal of Clinical Oncology published research supporting this new guideline. The report was called Use of Biomarkers to Guide Decisions on Adjuvant Systemic Therapy for Women With Early-Stage Invasive Breast Cancer: American Society of Clinical Oncology Clinical Practice Guideline Focused Update.

“Some women with breast cancer are more likely to have a recurrence of cancer and need to receive chemotherapy to lower this risk,” Vered Stearns, MD, co-chair of the ASCO expert panel that developed the guideline update, said in a statement.

The study followed more than 6,500 women with early-stage breast cancer who had received breast surgery and then underwent the MammaPrint (Agendia) genomic test. Findings show that this genomic test reduces the prescription of chemotherapy by 46 percent.

“The MammaPrint test can now be added to the list of tests that help clinicians identify women who need chemotherapy and those who do not,” said Dr. Stearns, co-director of the Breast Cancer Program at The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland.

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