PIK3CA and breast cancer: Efficacy of AIs as compared to tamoxifen have previously been explored and reported.18 In the analysis from the randomized BIG 1–98 trial, the authors demonstrated a greater magnitude of benefit with an AI letrozole in comparison to tamoxifen for patients with PIK3CA mutated early-stage breast cancer (HR 0.18; 95% CI 0.06 – 0.50).