Breast cancer patients had been treated with weekly paclitaxel for up to 12 weeks followed by four cycles of doxorubicin plus cyclophosphamide. After treatment, most patients had an increase in markers of metastasis with a few people increasing more than fivefold. More 50% of patients moved from low/intermediate- into a high-risk group for developing distant metastasis.

Mice with breast cancer tumors were also treated with the same chemo drugs and they were found to initially reduce tumor growth but they also increased blood vessel growth and repair mechanisms allowing for more aggressive tumors to grow and metastasize.