Breast-cancer tumours can become resistant to therapy if they express abnormally high levels of the gene for a protein called cyclin E. The finding suggests that a combination of drugs targeted at specific molecules may one day be appropriate for such tumours.

The therapeutic antibody trastuzumab is designed for breast cancers that overexpress the gene HER2, but patients frequently become resistant to the treatment. José Baselga, now at Massachusetts General Hospital in Boston, and his colleagues analysed tumour cells from 34 patients treated with trastuzumab. They found that the median time it took for tumour progression to recommence was cut by more than half in those whose tumours overexpressed cyclin E.

Cyclin E acts with another protein called CDK2 to usher cells through a specific phase in the cell cycle. A compound that inhibits CDK2 slowed the growth of trastuzumab-resistant tumour cells transplanted into mice.

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1014835108 (2011)