In embryos the growth of the tumors is stopped or slowed by proteins, called factors of stem cell differentiation, present during the process of formation of the organs. These factors are present both in the uterus of the mammals as well as in the embryos of oviparous and intervene to protect embryos from errors of transcription of the DNA that can occur during multiplication. Studies in test tubes have shown that these small peptides also inhibit the growth of tumor cell cultures.
The intuition of researchers was to compare a tumor cell to a stem cell: both in fact are characterized by fast multiplications. At a certain point, however, the stem cells of the embryo, following their biological program, stop in their multiplication and begin to differentiate; some become cells of the liver, others of the brain, others of the bones, and so on. In the tumor, instead, this is not foreseen and there is only a disordered growth.
Researchers have therefore been studying the reason why stem cells stop multiplying and begin to differentiate: they have discovered that the signal that induces this change comes from small proteins secreted by the stem themselves, the factors of stem cell differentiation.
It was then suggested that the same signals could also work with tumor cells and experiments in test-tube have confirmed this hypothesis: also tumors respond to the factors of stem cell differentiation.