A sequencing study of breast-cancer-tumor genomes suggests that cancers should be categorized by their genetic heritage, rather than where they reside in the body

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In recent years, scientists have come to appreciate that breast cancer is a complex disease, triggered by myriad genetic and lifestyle factors. But the latest study of the genetics behind the disease, published in the journal Nature, shows that it may actually be slightly simpler than researchers had thought.

As part of the Cancer Genome Atlas (TCGA), a government project that is aiming to sequence tumor genomes from dozens of different cancers to help scientists better understand tumor development and treatment, scientists sequenced 510 tumors from 507 patients with breast cancer. All told, they found 30,626 mutations in these cancer cells, but those aberrations fell into four main groups.

In one subtype, basal-like tumors that account for 10% of all breast cancers, the researchers found that the mutations resembled those found in ovarian cancers, thus explaining the link between the two diseases: women at higher risk of developing breast cancer are also more vulnerable to getting ovarian cancer.

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In two related subtypes, luminal A and luminal B, which include breast cancers that contain receptors for estrogen and progesterone, the scientists found that while the mutation rate in these cancers was lower, genetic aberrations occurred in a larger number of genes, suggesting that a more complex interaction of abnormal genes contribute to these types of breast cancer.

Teasing apart such connections will be critical for improving treatment for women with these mutations: those with luminal-A cancers generally have good outcomes, while those with luminal-B tumors have more mixed results. Isolating which mutations distinguish the two subtypes may help doctors treat women with luminal-B cancers in order to make them progress more like luminal-A cases, for example.

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In the final subtype, which are those that contain the HER2 receptors, the scientists found two smaller subgroups of HER2 cancers, which could explain why some women respond better to HER2-specific therapies like Herceptin than others. The good responders may have tumors with mutations that make the HER2 receptors more active and therefore enriched, making those cells better targets for the drug than those without the mutations.

Read more:
Genetic Study Identifies Four Main Types of Breast Cancer

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