Recently the relationship between shift time working and malignant neoplasms attracts attention. There is growing evidence suggesting that persons engaged in shift time work have much risk of causing cancer.
In 2007, the International Agency for Research on Cancer, a component agency of the World Health Organization (WHO) classified shift work with circadian disruption as a probable human carcinogen.
Dtsch Arztebl Int: Shift Work and Cancer The Evidence and the Challenge
Breast cancer has been most deeply investigated in terms of the relationship to the night shift, because the several associations of nurses were concerned with this issue. The majority of nurses are female, and a considerable amount of nurses are involved in night-shift work inevitably.
NHS Choice: Long-term night shifts can 'double' breast cancer risk
Very recently, Stockholm University in Sweden published the result of a large cohort study. According to the authors, women having engaged in night work for more than 20 years were likely to develop a breast cancer with 1.68 of Hazard Ratio. There was no significant risk found in shorter period.
BMJ Open: Night work and breast cancer in women: a Swedish cohort study
In the male, the development of prostate cancer is suspected to be relevant to night time work.
Mail Online: Men who work nights 'three times more likely to develop prostate cancer'
Conventionally, time shift working was considered to raise some health risks like vascular diseases and mental health problems. These finding above will strengthen the necessity of deliberate observation and care to such workers.
Some people are concerned about the possibility of increased lawsuits. In Denmark, female nurses and cabin attendants are subjected to the compensation when causing breast cancer. Will causing tumors be identified as an industrial accident in other countries?
Also, I have had duty work at night in the hospital for a decade. Ten years after now, I should be cautious about the risk of prostate cancer, as well as other health risks.