Whether particular subgroups of women with hormone receptor-positive early breast cancer might benefit more or less from the use of adjuvant endocrine therapy with an aromatase inhibitor compared with tamoxifen is of particular clinical relevance, but difficult to establish with any degree of certainty. For example, an exploratory analysis within ATAC suggested that the subset of women with oestrogen receptor-positive, progesterone receptor-negative breast cancers particularly benefited from the use of anastrozole. While there are plausible biological explanations for why this could be so, it is not a consistent finding across all trials (A. Howell, personal communication). This and other subgroup analyses (for example the effect of HER2 status) remain important questions for further research, but cannot be relied upon to inform current clinical practice.
Recommendations for Aromatase inhibitors as adjuvant endocrine therapy