After breast cancer surgery, women are prescribed adjuvant (or follow-up) therapies such as chemotherapy and endocrine drugs to reduce the risk of the cancer returning. It's been assumed that the treatment effects of these therapies remain constant over time, but a new study from the Cancer Therapy & Research Center (CTRC) at The University of Texas Health Science Center at San Antonio suggests the opposite is true.
The study, published this week in the Journal of the National Cancer Institute, looked at 19 breast cancer adjuvant therapy clinical trials of the National Surgical Adjuvant Breast and Bowel Project (NSABP). Therapies were evaluated for relative benefit, defined as the percentage by which they reduced recurrence and death among study participants.
Researchers found time-varying treatment effects of adjuvant therapies in nearly half of the trials (nine of 19). "In some trials, the benefit diminished at specific points of time after surgery," said study senior author Ismail Jatoi, M.D., Ph.D., FACS. "In other trials, there was no benefit early on, but then there was a delayed benefit that emerged more than one year after surgery."
In one clinical trial, the researchers found that a regimen provided initial benefit, but then a subsequent disadvantage, to patients, he said. Dr. Jatoi is the Dale H. Dorn Chair in Surgery in the School of Medicine at the UT Health Science Center, and serves as professor and chief of the Division of Surgical Oncology and Endocrine Surgery.
The findings may change the way oncologists talk to their patients about effects of treatments they are receiving, Dr. Jatoi said.
"We are seeing more and more long-term survivors of breast cancer who had these treatments many years ago," Dr. Jatoi said. "The question is, if these treatment effects have waned, should we consider extended adjuvant treatment regimens for the long term in some patients."
Adjuvant therapy trials should be designed and interpreted with this in mind, Dr. Jatoi said.
In 2011, Dr. Jatoi wrote a viewpoint article published in the Journal of Clinical Oncology in which he proposed that treatment effects of adjuvant therapy regimens might vary over time. He approached the NSABP, one of the nation's largest clinical trials groups, about doing a study. NSABP statisticians Hanna Bandos, Ph.D., and Jong Hyeon Jeong, Ph.D., conducted much of the work and are co-authors of the study.
More information: Ismail Jatoi et al. Time-Varying Effects of Breast Cancer Adjuvant Systemic Therapy, Journal of the National Cancer Institute (2015). DOI: 10.1093/jnci/djv304