According to this source there are five stages of a tumor: zero through four.Again Donnie Jr manages to prove that he's one of the short bus kids
"What I want to know is how did Dr. Jill Biden miss stage five metastatic cancer or is this yet another coverup???"~ Donald Trump Jr. #1,480

So perhaps Junior is struggling with the complexities of single digit arithmetic. - OR -
Perhaps the lesser Trump refers to the sixth stage, which by medical standard is "stage five", thermal ambience. Or as Rush Limbaugh phrased it, "... has assumed room temperature."
I miss you Rush. But if I ever see you crossing the street, I'll gun it anyway, even if only for nostalgic comfort.