They found the cancer cells of mother and baby carried the identical mutated cancer gene (called BCR-ABL1), but the infant had not inherited this gene.

But Gleevac, too, can be bypassed by further mutations of BCR-ABL which allow the tumour cells to grow in the presence of the drug.

There is already a targeted treatment for this disease. Gleevec, probably the most remarkable anti-cancer drug of the past decade, disables the protein encoded by another fused gene, BCR-ABL.