Bosutinib: a new drug that increases progression free survival in patients with locally advanced or metastatic breast cancer

This paper presents the results of a clinical study which looked at the use of a new drug called Bosutinib (Bosulif) for the treatment of breast cancers diagnosed as being stage III or IV. In patients previously treated with chemotherapy, Bosutinib showed promising efficacy in delaying cancer progression.

Locally advanced or stage III cancers have spread from the original site into neighboring tissue and lymph nodes. Metastasized or stage IV cancers have spread from the breast to other organs of the body.

Bosutinib was designed as a drug to target a specific protein of the tyrosine kinase family, called Src.  Tyrosine kinases are enzymes which act as “on” and “off” switches for many cell functions.  Src is involved in cell growth and has been found in higher concentrations than normal in patients with breast cancer.

Women included in this study had stage III or IV cancers which had progressed since their previous chemotherapy. These cancers were not curable with currently available treatments. Patients received a single daily oral dose of Bosutinib for as long as they could tolerate the treatment or until their cancer progressed.

Overall, 73 patients were treated with Bosutinib. 16 weeks after starting the treatment, 39.6% of patients had no disease progression (‘progression free survival’). 26.4% of the study participants survived the 2-year follow up period.  43.1% of patients with hormone receptor positive and 41.7% of those with HER2 positive breast cancer had no disease progression at 16 weeks. For those who had triple-negative breast cancers, the rate was lower: 25%.

Bosutinib was generally well tolerated, although patients did experience side effects like diarrhea, nausea and vomiting.  The drug was found to have benefits over another drug called Dasatinib which works in the same way as Bosutinib.  Only 6% of patients on Bosutinib suffered from anemia (deficiency of red blood cells or hemoglobin in the blood) compared to 66% of patients on Dasatinib.

In summary, Bosutinib showed promising efficacy in delaying cancer progression in patients with locally advanced or metastatic breast cancer, previously treated with chemotherapy. This effect was pronounced in patients with receptor positive cancers. Bosutinib was generally well tolerated, with the main side effects being related to the digestive system.

We would like to emphasize that this is a phase II clinical trial, performed on a small amount of patients to evaluate drug efficacy and safety. Larger trials are needed to further establish this drug’s therapeutic potential.