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Newswise A method called molecular subtyping can help doctors better determine which of their breast cancer patients are at high risk of getting breast cancer again, a new study led by the University of South Florida reports. This sophisticated genetic profiling of an individuals specific tumor offers an additional resource to help identify patients who would most benefit from chemotherapy and those who would not.

The findings by researchers from USF and other institutions were presented in a scientific poster at the Miami Breast Cancer Conference, held March 6-9 in Miami Beach, Fla.

The most important takeaway for our colleagues in breast cancer diagnosis and treatment is the potential value of molecular subtyping to personalize and improve each womans treatment, said principal investigator Charles E. Cox, MD, McCann Foundation Endowed Professor of Breast Surgery, USF Health Morsani College of Medicine.

Molecular subtyping is a way of classifying breast cancer tumors into one of four genetically-distinct categories, or subtypes: Luminal A, Luminal B, Basal (a subset of triple negative), and HER2-type. Each subtype responds differently to different kinds of treatments, and some subtypes indicate a higher risk of disease recurrence.

Our data showed that a substantial number of breast cancer patients -- classified as low risk by one particular genomic test -- turn out to be at high risk of recurrence once we determined their subtype, Dr. Cox said. These are mostly Luminal B patients, and their physicians might not fully understand their patients situation unless they do subtyping.

The USF study examined why different genomic tests for breast cancer sometimes provide contradictory information about risk of recurrence. The key findings involved the 70-gene MammaPrint test; the 21-gene Oncotype DX test, which is an earlier commercially available test; and Mammostrat, a gene profiling test performed on slides of the breast tumor by a pathologist. The tests have generally been assumed to provide equivalent information about recurrence risk, but that is proving not to be the case.

Researchers examined tumor samples from a total of 148 patients. The greatest discordance (lack of agreement) about risk of disease recurrence occurred in a group of 51 patients. Of those 51, all were stratified by MammaPrint as high risk of recurrence, while Oncotype classified 18 of them (35 percent) as low risk.

BluePrint, an 80-gene test to identify a tumors molecular subtype, was also used for those stratified by MammaPrint. This process revealed that the 51 patients were Luminal B, a molecular subtype with a high risk of recurrence.

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Molecular Subtyping of Breast Cancer Can Better Identify Women at High Risk of Disease Recurrence