Breast cancer in nurses: is working many night shifts linked to hormone-related tumor types?

Statistically significant associations were found between breast cancer and work durations of ≥ 5 years with ≥ 6 consecutive night shifts, particularly for progesterone receptor-positive tumors (odds ratio = 2.4).

• The study involved 513 nurses diagnosed with breast cancer and 757 matched controls.
• Increased risk of breast cancer is associated with working night shifts for 5 or more years.
• The highest risk was specifically linked to progesterone receptor-positive tumors.
• A borderline significant difference was noted in postmenopausal women between progesterone receptor-positive and negative tumors based on night shift work.
• The findings suggest a potential role of progesterone in the effects of night work on breast cancer.

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