Assassination by cancer?

Is the United States's government trying to assassinate left wing Latin American leaders by infecting them with cancer?

According to Hugo Chavez, the answer is maybe.  In a recent article by the BBC , Chavez conjectured that it was "difficult to explain using the law of probabilities" that while he was fighting cancer, according to the BBC, "Fernando Lugo of Paraguay, Dilma Rousseff of Brazil and her predecessor Lula have also had cancer.".  Chavez noted that the fact that the U.S. infected Guatemalan prisoners with syphilis in the 1940's shows the United States has the means and motives to use weaponized infectious diseases to kill off her political enemies.