At some point in its past, the Cancerverse could be called a copy of Earth-616. Their stories were almost identical, until Captain Marvel's accident became the point where their Timelines diverged.
The first Captain Marvel was Mar-Vell, the Kree spy sent to Earth. He had originally been dispatched by the Supreme Intelligence to sabotage Project Pegasus's development of spacecraft engines.
But as he came into contact with more and more humans on Earth, he was gradually assimilated by human Civilization. He preferred the richness of human emotions to the Kree Empire's cold, quantified organization of everything.
So he betrayed the Kree. Using the Negative Particle Bracelet granted to him by the Supreme Intelligence, he fought for justice as a Superhero and even developed feelings for Carol, who had been a test pilot at the time.
But another coworker at the facility had secretly loved Carol as well. That man became the Super Villain Nitro in an accident. His ability was an endlessly reusable "self-destructing nuclear bomb": he could trigger physical reactions within his body to blow himself up, then reconstruct himself from his atomic state.
To compete for Carol's mating rights, Nitro attacked Captain Marvel, Mar-Vell. At the same time, the Supreme Intelligence sent a team of subordinates to eliminate the Traitor.
Thus, the three sides descended into a chaotic battle. To protect Carol, who had happened to pass by, Mar-Vell endured both a nuclear explosion and the self-destruction of an alien engine head-on.
Although he drove back his enemies at the time, he also suffered irreversible injuries and developed even more varieties of cancer than Deadpool.
Remember? Deadpool's dick, balls, and eyeballs weren't cancerous. Mar-Vell was different—he got every cancer there was. Even with the Negative Particle Bracelet, he could not fight this terrifying incurable disease and could only