Most life on Earth is microbes. we've only just scratched the surface of the microbial realm. Probably less than .1% of microbes have been classified let alone cultured or had their genes sequenced, so really that microbial realm is a mystery.
When I was a student almost nobody thought there was any life beyond Earth. Today it's fashionable to say that there is life all over the place, that the universe is teeming with it, but the scientific facts on the ground haven't really changed.
Cancer is not something confined to human beings. It's found in all multi cellular organisms where the adult cells proliferate, so it's widespread in the biosphere. It's a phenomenon that is deeply related to the history of life itself, so by studying cancer I think we can illuminate the history of life itself and vice versa.
I should say we know that there are many, many other Earths out there. We're almost certain that there will be upwards of a billion Earth-like planets in our galaxy alone, so there is no lack of real estate where life might happen, but what we don't know is how likely it is given the real estate, given a wonderful pristine planet like Earth how likely is it that life will pop up inhabited? We don't know the answer to that.
It's worth remembering that all technology leaves a footprint. For example, our own technology is leaving a footprint in terms of global warming, which could be detected from a long way away. One assumes that a very advanced civilization that has been around maybe millions and millions of years would have an even bigger footprint that might extend beyond its planet to its immediate astronomical environment.
It's only fashion that has said the pendulum has swung from extreme skepticism about extraterrestrial life to extreme credulity. The truth is somewhere in between.
