Cancer is caused by mutations in human DNA. Several lines of genetic code are deleted or mixed together, and this change allows cells to proliferate and grow in abnormal ways. Sometimes these DNA changes are hereditary-people inherit them from their parents-but sometimes they are caused by environmental factors. Understanding the tumor’s DNA can help create targeted gene therapies to combat it.
for many years, Epidemiological studies Has shown Thyroid cancer It is especially common in people exposed to radioactive iodine, especially those exposed to radioactive iodine during childhood. At a high enough dose, radioactive iodine will kill thyroid cells and can actually be used as radioactive iodine. treatment Used for thyroid cancer and other thyroid diseases. But Chernobyl’s radiation is not enough to kill cells. Morton said that instead, months of lower-dose exposure caused cell changes that could lead to tumors.
In her paper, Morton and her colleagues were able to carefully study the tumors of people living near Chernobyl, studying the DNA of more than 350 young children who developed thyroid cancer after exposure to radiation. They drew a comprehensive molecular map of these tumors. Then, in order to understand how they are different from thyroid cancer caused by other factors, the researchers compared these tumors with the tissues of 81 people who were born near Chernobyl after 1986 and developed thyroid cancer but were never exposed to radiation. For comparison. They also compared the tumor with data from the Cancer Genome Atlas, which characterizes the genomes of thousands of cancers.
They found that cancer cases caused by exposure to radioactive iodine after thawing mutated the genes by breaking the double strands of DNA and separating them. In contrast, the thyroid cancer in the Cancer Genome Atlas and the thyroid cancer in the control group of 81 unexposed people in the region are more likely to be caused by a single point mutation in which only a single DNA base pair is changed.
After the disaster, scientists monitored many communities near Chernobyl, as well as workers responsible for cleaning up the radioactive reactor and putting it in steel and concrete sarcophagi. Researchers also conducted extensive interviews with residents about indirect contact with residents. For example, radioisotopes from the reactor fell into the surrounding fields and were eaten by cattle grazing, and then spread the radiation to their milk, and then to the people who drink it. Therefore, information about the consumption of dairy products provides clues about how much radiation someone has been exposed to. Physicists and epidemiologists work together to decompose all these direct and indirect measurements into the radiation doses that people who donate tissue samples will receive. “This is a unique situation, and we know a lot about exposure,” Chanock said. “Most large-scale genomic landscape studies have no information about people’s geographic location and exposure.”
This provides researchers with an opportunity to carefully study the exact course of the cancer process. They found that the more radiation a person was exposed to and the younger they were at the time of exposure, the more double-stranded DNA breaks they had.
Finally, the research team studied the driving factors of cancer, that is, specific genes that lead to tumor growth. They found that the molecular characteristics of cancers caused by radiation are no different from those observed in randomly occurring thyroid cancers. It’s just a different reason (double-stranded DNA break). “This really made us understand how radiation causes cancer,” Morton said.
There are no special biomarkers to mark these cells as mutated by radiation, which tells scientists that the effects of radiation occur in the early stages of the carcinogenic process, and as the cancer develops, these biomarkers (if any) will be lost or lost. Wash off. . The molecular similarity suggests that these cases do not require novel treatments. She said: “These cancers end up looking like typical thyroid cancer, so there is no special significance to other treatments.”