This real-world retrospective analysis evaluated the effect of first-line palbociclib plus an aromatase inhibitor (AI) versus AI alone on tumor responses in pre/perimenopausal women with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer.

The real-world response rates associated with palbociclib plus an AI were numerically higher than those associated with an AI alone.

These results suggest that pre/perimenopausal women with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer appear more likely to respond to palbociclib plus an AI than an AI alone in the first-line setting.