Interval cancers showed a lower degree of differentiation and phenotypes associated with a worse prognosis compared to screen-detected cancers, with a higher proportion of ER − (20.7% vs 7%; p = 0.005), PR − (31% vs 18%; p = 0.045), HER2 + (12.1% vs 2.9%; p = 0.031), and Ki67 values ≥ 20% (50% vs 18.9%; p < 0.001). This evidence concerns the gene PGR and cancer.