Biomarker Assay Evaluates Efficacy of Novel Breast Cancer Drug

Breast cancer is the most common form of cancer among women today, affecting approximately 362,000 individuals in the European Union (EU) and 233,000 in the USA each year. Around 1,600 new cases are diagnosed every day and 136,000 deaths occur annually (EU+USA).

Palbociclib, a drug for the treatment of estrogen receptor (ER)-positive and HER2-negative breast cancer, was FDA-approved in February 2015. In the drug’s first year on the US market, more than 20,000 women were prescribed the medicine, whose sales are estimated to exceed USD 2 billion in 2016. In November 2016 palbociclib was approved in the EU.

Scientists at Washington University School of Medicine investigated 50 women with clinical stage II or III ER- positive, HER2 negative breast cancer, treated with anastrozole in combination with palbociclib prior to surgery. DiviTum was used to measure levels of thymidine kinase (TK) activity, an enzyme closely linked to cell proliferation rate, in blood samples collected before and after treatment. DiviTum is a highly sensitive assay for measuring cell proliferation.

Since one of the most fundamental characteristics of cancer is uncontrolled and increased cell growth, DiviTum enables valuable prediction capability and monitoring of compounds regulating cell proliferation and the cell cycle. The results demonstrated a highly significant correlation between the anti-proliferative effect of palbociclib and the reduction in TK levels measured by DiviTum post two weeks of adding palbociclib and at the time of surgery. The assay may thus serve as an early indicator of treatment response by cyclin-dependent kinase (CDK) 4/6 inhibitors like palbociclib.

Dr. Cynthia Ma, MD, PhD, an Associate Professor of Medicine and the lead investigator on the study said, “Our study provides the first clinical evidence of a method, DiviTum, for palbociclib treatment effect in breast cancer. The results are very promising and support future studies of DiviTum to evaluate and identify patients for response to CDK 4/6 inhibitors.” The study was presented at the San Antonio Breast Cancer Symposium, held December 6-10, 2016, in San Antonio, TX, USA.