AnneMarie Ciccarella, a fast-talking 57-year-old brunette with a more than a hint of a New York accent, thought she knew a lot about breast cancer. Her mother was diagnosed with the disease in 1987, and several other female relatives also developed it. When doctors found a suspicious lump in one of her breasts that turned out to be cancer, she immediately sought out testing to look for mutations in the two BRCA genes, which between them account for around 20 per cent of families with a strong history of breast cancer.

Ciccarella assumed her results would be positive. They weren’t. Instead, they identified only what’s known as a variant of unknown or uncertain significance (VUS)—or two of them, one in both BRCA1 and BRCA2. Unlike pathogenic mutations that are known to cause disease or benign ones that don’t, these genetic variations just aren’t understood enough to know if they cause problems or not.