London, Oct 15 (IANS): Chronic jet lag alters the microenvironment surrounding tumour cells, making it more favourable for tumour growth, and also hinders the body's natural immune defences, warn researchers.

The study, published in the journal 'Science Advances', also helps explain why some tumours win the race when a person is exposed to the chronically stressful conditions that occur when the environment and the body's clocks are misaligned.

"A key takeaway from this study is that if someone has a proliferative disorder, in this case, melanoma, doing shift work or regularly changing time zones could exacerbate the problem by dampening immune system response to tumour growth," said study author Diego Golombek from the National University of Quilmes in Argentina.

According to the researchers, every cell in your body has its own set of molecular clocks -- a series of genes, proteins, and signalling chemicals that set the pace for cell growth, division, and decay.

In cancer cells, these clocks are often altered, which allows the tumour to set its own pace for rapid, unchecked proliferation.

The researchers wanted to know how chronic jet lag impacts the microenvironment surrounding cancer cells and examined two groups of mice that were injected with melanoma cells.

The first group was exposed to a normal circadian schedule: 12 hours of light and 12 hours of dark. The second group's light and dark exposure were shifted by six hours every two days -- the equivalent of roaming across 21 time zones per week.

A month later, the scientists observed that the tumours in the jet-lagged group were roughly three times the size of the control group.

They also examined samples from the microenvironment surrounding the tumour, the spleen, which produces immune cells, and the liver.

The researchers found peculiar contrasts in how the immune system responded to the tumour.

For example, the levels of different types of immune cells called macrophages were inverted to be more prone to accept tumour growth in the jet-lagged group.

Similarly, the rhythms of other immune cells and molecules, including cytokines, were disrupted.

Even though the tumours didn't spread into their neighbouring organ, the liver, or the spleen, the scientists observed that the circadian variations in the immune system in both of these organs were deregulated.

"We combined two different approaches of chronobiology research to study the effects of circadian desynchronization on both tumour growth and immune rhythms, and we found a link," Golombek noted.