The disruptions to sleep patterns makes sense but I wouldn't have guessed the end results could be so serious. The Guardian:
In the latest study, from the Danish Cancer Society's institute of epidemiology, those who had worked nights at least three times a week for at least six years were more than twice as likely to have the disease as those who had not. But there was "a neutral link" for those who worked only one or two night shifts per week.
The study also challenged a hypothesis that less exposure to the sun and vitamin D might be a risk factor for those women who worked night shifts. The researchers found that in fact night workers tended to sunbathe more than those who worked during the day.
Night work can not only disrupt body clocks and result in sleep deprivation, however. It has been argued that it also suppresses production of the hormone melatonin and other metabolic and physiological processes that may increase the growth of tumours.