Dr. Portwine completed her medical school training at The University of Toronto in 1988.  She went on to do her Pediatric Residency Training from 1989 – 1992 and subsequently her subspecialty training in Pediatric Hematology/Oncology from 1992-1994 at the Hospital for Sick Children (HSC) in Toronto. Dr. Portwine completed a PhD in Molecular Oncology focusing on the inherited cancer susceptibility gene, p53, in March 2002 in conjunction with the Clinician Investigator Program at the University of Toronto. She was on staff as an Assistant Professor in the Division of Hematology/Oncology at HSC while completing her PhD from 2000-2001. In February of 2002, Dr. Portwine joined the Division of Hematology/Oncology in the Department of Pediatrics at McMaster University as a Clinical Assistant and then became a faculty member with the title of Assistant Professor within the Department.  She was promoted to the rank of Associate Professor in July 2008.

Since beginning at McMaster, Dr. Portwine has become the local Principle Investigator for several clinical trial consortiums, including the Children's Oncology Group and the Histiocytosis Society. She became Education Program Director in July 2008 in order to focus on her interest in teaching. Research in fertility and quality of life issues in the oncology population is ongoing.  She sits on several committees including the Mortality Review Committee, has been engaged in Provincial and National Guidelines development in the care of pediatric oncology patients, and has been involved in developing patient education materials for the adolescent population. Dr. Portwine has also been involved in the process of PET funding for oncology patients and is a member of the group attempting to establish an Adolescent and Young Adult Oncology Unit in Hamilton. She currently sits on the Board of Directors for Camp Trillium which is a camp focused on children with cancer and their families.