Could Aliens Get Cancer?
We as humans only know too well the scourge of cancer. If we want to find out whether aliens could get cancer, we have to investigate whether cancer is something unique to life on our planet or a universal problem that would also occur in an alien biosphere.
To answer this question, we have to understand what cancer is. One of my previous Ph.D. students, Marina Walther-Antonio, who now works at the Mayo Clinic in Rochester, Minnesota, and I attempted just that a few years ago. We suggested that the underlying cause of cancer is when certain cells are exposed to stress such as toxins, viruses, or radiation, they revert to an ancient unicellular mode of survival, disconnect from the collective, reproduce rapidly, and spread to new locations for colonization (called metastasis in the case of cancer cells). Alfonso Davila from NASA Ames and Pedro Zamorano from the University of Antofagasta in Chile tightened the evolutionary argument. They claimed that cancer cells revert to the earliest stage of the evolution of eukaryotes to a time when the first single-cell life forms appeared on Earth and had a nucleus that was more complex than bacteria. If so, this would explain why cancer cells are optimized for survival and reproduction in oxygen-poor micro-environments.
The evolutionary approach to understanding cancer explains why we see the disease in all animals on our planet. Some animals are more susceptible to cancer than others, and some animals have evolved special ways of protecting from it, like the naked mole-rat, but all can get it. Generally, the more complex an organism is, the more often cancer seems to be a problem and not only in advanced age. There is even contagious cancer, which can occur in dogs, The Tasmanian devil, the Syrian hamster, and certain clams. Contagious cancer is very rare and is spread by clonal cells or viruses, but in the case of The Tasmanian devil, it nearly led to its extinction.
But what about other multicellular life on our planet? Plants can exhibit cancerous growth, which is a uncontrolled reproduction of plant cells around an infection and similar to a tumor in animals. Typically, the cancerous growth are crown galls, which exhibit the above-mentioned oxygen-poor conditions in their interior. However, because plant cells are not mobile but well-anchored and surrounded by cell walls, metastasis is not known to occur in plants. And what about fungi? I could not find much research on that, but it looks like they can’t get cancer. Most fungi are single-cellular or have single-cellular stages during which fast reproduction is advantageous. And when fungi are in their multicellular stage, like in the case of mushrooms, cells don't really divide anymore but only expand in size.
So, what about intelligent aliens? They would be expected to have undergone a similar evolutionary selection process as humans did. Intelligent aliens would be mobile animal-type organisms exposed to predator-prey relationships and likely develop complex social relationships. Intelligent life forms on our planet have a sophisticated circulatory system, making them susceptible to metastasis – the most serious problem with cancer. Thus, if these aliens were in our stage of development and organic beings based on biology, they would most likely be susceptible to cancer. Unless they developed further and are masters of genetic engineering or have evolved to become advanced mechanical entities.