Nov. 27 (UPI) -- Scientists have uncovered a unique evolutionary and physiological link between mammalian pregnancy and fast-spreading cancers.
In many mammals, including humans, the placenta embeds itself into the wall of the uterus. The placenta's invasion of the uterus lining looks a lot like the way cancer cells spread.
Not all mammals grow aggressively invasive placentas. The placentas of horses, cows and pigs don't attach themselves to the wall of the uterus. In the same animals, cancer rarely metastasizes.
To better understand this dichotomy, scientists set out to study the evolution of invasibility in the stroma, the connective tissue that provides structural support for different cells, tissue and organs.
"Previous research has shown that cancer progression in humans includes the reactivation of embryonic gene expression normally controlling placenta development and immune evasion," Günter Wagner, a professor of ecology and evolutionary biology at Yale University, said in a news release. "We wanted to find out why, for example, melanoma occurs in bovines and equines but remains largely benign, while it is highly malignant in humans."
Scientists compared the rates of cancer cell invasion in cow and human models, and engineered gene expression experiments to identify genes that influence the invasibility of the human stroma.
"Gene expression profiling identified genes with high expression in human but not in bovine fibroblasts," researchers wrote in their paper.
When researchers tweaked the genetic expression patterns of fibroblast cells in humans to mimic the expression patterns observed in cows, the cells proved more resilient to invasive melanoma.
The findings, published this week in the journal Nature Ecology and Evolution, suggest the difference in malignancy rates among different mammal species is rooted in differences in the genes controlling the invasibility of stroma tissue.
The adaptations that aid the development of the fetus inside mammals like apes and humans likely make the same species more susceptible to deadly, fast-spreading cancers later in life.
In the future, doctors may be able to alter a patient's gene expression to make their stroma cells more resistant to the spread of cancer, the researchers suggest.