Wrong. I remembered reading Deadpool's back story long before this movie. A little romp onto wiki found this: (bolded the important part)
Powers, abilities, and equipment
Deadpool has been artificially endowed with a superhuman regenerative healing factor by the Weapon X program that is at times shown to be superior to that of Wolverine's or Sabretooth's. As Deadpool had cancer at the time of the gene therapy, it has been suppressed by the "healing factor", which continually regenerates every cell in Deadpool's body, keeping the cancer at bay. However, an unanticipated side effect resulted in a rapid acceleration of the tumors as well, causing them to quickly spread across his entire body as soon as his powers fully activated. Though the healing factor keeps them from becoming what would otherwise be a horribly debilitating condition, this causes his body to be in a constant state of flux and regeneration. His powers' full manifestation also appeared to contribute to his insanity, he himself declared awareness of a growing detachment from reality moments after. Removal of his powers would cause him a cancer relapse, as he himself is aware. As a by-product of his healing factor, he possess enhanced strength, agility, and reflexes.
The healing factor enables him to regenerate damaged or destroyed tissue with much greater speed and efficiency than an ordinary human. He can regenerate whole organs and even severed limbs. In at least one instance, Deadpool, after breaking nearly every bone in his body, strapped himself to a rack so his bones set properly. He has survived being decapitated, though his head did not regenerate; it was simply replaced and healed back to his torso.[53] Deadpool can also come back from the dead, as a direct result of his healing ability. The reason for this is unknown.[54] This has the apparent effect of slowly causing Deadpool to become more insane every time he dies, to the point of sociopathy, hallucinations, and multiple personality disorder.