For postmenopausal women with hormone receptor positive early breast cancer, 5 years of aromatase inhibitor, typically letrozole, has become the standard of care in the adjuvant setting. In this chronic relapsing form of cancer, it has not been clear if there is a benefit tied to extending AI therapy beyond 5 years but findings from the MA.17R trial presented at ASCO today are the first data on this crucial question.
With adjuvant hormone therapy, a major portion of the benefit comes from the prevention of contralateral breast cancer, but there is only a small reduction in distant recurrence. MA.17R was able to show that 10 years of AI therapy can reduce recurrence by 34%. End points focusing on the long-term toxicity of letrozole demonstrate that the effects on bone, cardiovascular, and CNS are numerically smaller that commonly assumed but there is a clear need for more studies including research on the quality of life of patients on hormone therapy.
Data have shown that a small but important subgroup of women is at a continuing risk of late relapse, and with these new and important findings researchers concentrate on developing an algorithm based on both clinical and genomic parameters to better identify those patients.