The study offered statistically significant data on the impact that long-term night work (≥5 years) with 6 or more consecutive shifts have on the increased risk of breast cancer, noting significant associations and an increased risk for tumors with positive progesterone receptors (OR = 2.4, CI 95%: 1.3–4.3; p = 0.01). Here, PGR is linked to breast carcinoma.