Working at nights raises breast cancer risk Women who work long-term night-shift jobs - including nurses, cleaners, care workers and call-centre handlers - are twice as likely to develop breast cancer as those who do normal hours, research suggests. Canadian researchers examined 1,134 women with breast cancer and 1,179 women without the disease, but of the same age. Women were questioned about their work and shift patterns and researchers also assessed hospital records of the women who suffered from the disease. The research, led by Queen's University in Kingston, adds further evidence of the potential risks incurred by women who work night shifts. This study found that the associations were similar among those who worked in healthcare and those who did not.