No statistically significant differences were detected between interval cancers in the study and control populations in the degree of histological differentiation (p = 0.391), percentage of oestrogen receptor positive (ER +) (66.7% vs 79.1%; p = 0.562), progesterone receptor positive (PR +) (60% vs 67.4%; p = 0.840), human epidermal growth factor receptor 2 positive (HER2 +) (13.3% vs 11.6%; p = 0.840), or percentage with Ki67 values > 20% (53.3% vs 48.8%; p = 0.857). This evidence concerns the gene PGR and cancer.