When a new study examined more than 1,700 breast tumors, including 412 triple-negative breast cancers, its researchers concluded that triple-negative cancers and basal-like breast cancers should not be considered as a single type. More than 30% of triple-negative cancers lack biological markers associated with basal-like tumors. Thus, triple-negative breast cancers are more biologically diverse than previously believed and classification should be expanded to reflect this heterogeneity.

Breast cancers are sometimes classified into four main subtypes: basal-like (often called triple-negative), luminal A, luminal B, and HER2-enriched. While targeted therapies have been developed to exploit the weaknesses of some types of breast cancers, the lack of these drug markers on triple-negative cancers means patients with these tumors must undergo broader, more aggressive therapies.

“This is clinically very important, because triple-negative breast cancers lack the three biomarkers used for guiding many therapies in breast cancer, so those patients do not have these therapeutic options. They are thus left with multiagent chemotherapy as their treatment,” said Charles Perou, PhD, of University of North Carolina Lineberger Comprehensive Cancer Center in Chapel Hill, North Carolina.

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The researchers found at least four disease subtypes within triple-negative tumors, with more than 75% of the tumors falling into the basal-like subtype. Further research is needed to identify the distinct biomarkers shared by the expanded subtypes of triple-negative cancers. The ultimate goal will be to target the individual biomarkers of these subtypes and create therapies that target their individual biology, according to Perou.

“Today, given that the basal-like subtype is the majority of triple-negative patients, I believe that if we are to make therapeutic progress against triple-negative disease, we are going to need to target the unique biology of the basal-like subtype” said Perou. This study was published in The Oncologist (2013; doi:10.1634/theoncologist.2011-S1-61).