The Earth's gravity, or its absence, affects not only our ability to keep to the ground, but also affects the expression of genes.
In the case of cancer, some tumours are much less aggressive in the micro-gravity environment of space compared to their behaviour on earth, researchers have found.
The observation can help scientists understand the mechanism involved and develop drugs targeting tumours that do not respond to current treatments.
"Micro-gravity can be approximated on earth but we know from the past that simulated micro-gravity is not the same as the real thing," said Daniela Gabriele Grimm from the Aarhus University in Denmark.
True weightlessness affects human cells in a number of ways.
Without gravitational pull, cells form three-dimensional aggregates or spheroids.
"Spheroids from cancer cells share many similarities with metastases - the cancer cells which spread throughout the body. Determining the molecular mechanisms behind spheroid formation might therefore improve our understanding of how cancer spreads," Grimm said.
Cells grown in space and in simulated micro-gravity on the ground were analysed for changes in gene expression and secretion profiles.
The results suggested decreased expression of genes that indicate high malignancy in cancer cells.
The overall goal is to find as many genes and proteins as possible that are affected by micro-gravity and to identify the cellular activities they influence, said the research published in the FASEB Journal.