Why has only 1 United States President died from cancer?

From my research only Ulysses S Grant has died from cancer. Statistically out of 43 presidents we should have had at least 13 presidents die from cancer.

Why has only 1 United States President died from cancer?
Who cares?!
Reply:because the rich man in the U.S. gets great medical.
Reply:because only one president had cancer.
Reply:It's a conspiracy!
Reply:caus their darn rich
Reply:President Reagen had cancer; he had surgery while in the White House to remove it. They get really good health care. You either get more cancer with really good health care or less. Go figure.
Reply:If you are dealing with statistics, you should know that the sampling size of 43 is too small to draw good data from.
Reply:Believe me man, those guys ain't fully human. Kinda like half human, half alien reptilian. No joke.
Reply:It could be very well on diseases that people don't know what they have and they need a check-up for that.