Last update:
01-Dec-2010

Shift-work is defined as work in which one employee is changed with another employee in work delivery, while the function of the business is continuous. Approximately 15–20% of the working population in Europe and the USA is involved in shift-work, mainly in the fields of health care, industry, communication and entertainment. In 2007, the International Agency for Research on Cancer (IARC) concluded that "shift-work which includes disruption of circadian rhythm is potentially carcinogenic to humans", and classified night work from possible to probable carcinogen (group 2A). The aim of this paper is to review the recent literature on the relationship between shift-work and carcinogenesis, and more specifically, with reference to forms of cancer for which there are already epidemiological reports. With regards to breast cancer, which is the leading cause of death from cancer in the female population Nightworldwide, studies provide indications of a causal relationship. In view of this evidence, the theory of R.G. Stevens, as suggested in 1987, that light-at-night is a risk factor for breast cancer, could account for at least a small percentage of the differences in rates of breast cancer worldwide. As far as prostate, endometrial and colorectal cancers and lymphoma are concerned, rare epidemiological studies and laboratory findings have been documented. In parallel, later data on the possible pathophysiological basis of such a relationship are reviewed. The suggested mechanisms of shift-work mediated disruption of circadian rhythms at the cellular level include (a) suppression of melatonin secretion, which could lead to oncogenesis, and (b) direct suppression of the genes controlling the circadian rhythm, which could lead to changes in the regulation of the cell cycle. The retrieved data are reviewed in association with the role of occupational medicine, and the need is emphasized for the design and implementation of studies to assess this possible relationship from the viewpoint of the interests of the employees.

Key words: Breast cancer, Cancer, Melatonin, Night work, Shift-work.