- two commonly used drugs encourage the disease to develop in the lungs

• Paclitaxel and doxorubicin cause breast tumours to release fluid-filled sacs
• These sacs contain proteins that then circulate in the blood to the lungs
• Proteins then trigger the release of other proteins and immune cells  
• These immune cells are linked to the survival and growth of lung tumours 

Chemotherapy may cause breast cancer to spread, alarming research suggests.

The commonly prescribed chemo drugs paclitaxel and doxorubicin cause breast tumours to release proteins that then circulate in the blood until they reach the lungs, triggering the disease's onset in a new part of the body.

When scientists blocked this protein in a lab model, the cancer did not spread. They hope their findings will help make chemotherapy more effective.