Professor Tjan-Heijnen obtained her medical degree from Radboud University, Nijmegen, Netherlands. She currently works as a medical oncologist at MUMC+ Comprehensive Cancer Center, Maastricht, Netherlands. Her main field of interest is breast cancer, more specifically focusing on young women with a wish for fertility preservation, and on metastatic breast cancer.

She is the past president of the National Breast Cancer Organisation of the Netherlands and initiated the NABON-Breast Cancer Audit, which annually assesses the quality of breast cancer care in Dutch hospitals. She was chair of the Dutch committee for the assessment of oncological drugs (BOM) and initiator and first director of the Comprehensive Cancer Network South-East Netherlands (OncoZON), involving 11 institutes (2010–2015).

Currently, Professor Tjan-Heijnen chairs the metastatic breast cancer team within OncoZON. Her research focuses on quality of care in daily practice and cost-effective implementation of new treatments. She initiated several Dutch breast cancer studies (Two-to-Six, INTENS, DATA, MIRROR, SONABRE) and is involved in many international studies. She has (co)authored over 300 peer-reviewed full papers and has been the supervisor of 50 PhD students.