Table 1.

Main neoadjuvant endocrine trials.

Clinical trials	Clinical response	Ki67 outcome
P024 (40–42)	ORR letrozole 55% vs. tamoxifen 36% (P < 0.001); ultrasound response letrozole 35% vs. tamoxifen 25% (P < 0.05); mammographic response letrozole 34% vs. tamoxifen 16% (P < 0.001); breast-conserving surgery letrozole 45% vs. tamoxifen 35% (P = 0.022).	No interaction with treatment-induced changes in Ki67 or absolute posttreatment Ki67 levels in either tamoxifen- or letrozole-treated tumor samples. Letrozole inhibited Ki67 to a greater extent than tamoxifen did (Ki67 geometric mean reduction 87% vs. 75%, respectively; P = 0.0009).
IMPACT (39)	There were no significant differences in OR in anastrozole, tamoxifen, or combination.	Greater Ki67 reduction in anastrozole arm. Ki67 geometric mean reduction: anastrozole 76% at 2 weeks/82% at 12 weeks; tamoxifen 59% at 2 weeks/62% at 12 weeks; combination 64% at 2 weeks/61% at 12 weeks.
ACOSOG Z1031 (43)	CRR letrozole 75% vs. exemestane 63% vs. anastrozole 69%.	No significance difference in Ki67 geometric mean reduction. Anastrozole 79% vs. exemestane 79% vs. letrozole 82%. Ki67-based data are closely equivalent with the data in adjuvant endocrine trials, therefore predicting similar activity as adjuvant therapies.
PROACT (44)	In hormonal therapy-only patients, ORR favored anastrozole arm (anastrozole 33% vs. tamoxifen 27%, P = 0.04), feasible surgery at baseline improved after 3 months in 43% of patients receiving anastrozole and 31% receiving tamoxifen (P = 0.04).	No data about Ki67

ORR, overall response rate; CRR, complete response rate.