Consistently, PI3K signaling and stemness scores were highest in the more aggressive PAM50 breast cancer subtypes (Fig 3B), including Basal, HER2 and Luminal B. These findings are in line with independent studies relying on alternative indices and methods for quantifying PI3K signaling and stemness in separate analyses [20,22,31,33–35]. Here, PIK3CA is linked to breast cancer.