請問一則幽默英文笑話,從The.Haunting.In.Connecticut看到的,我找到出處,可是還是不知到哪裡好笑?

影片中,媽媽開車載著有病的小孩,

小孩說了這個笑話,

A guy goes to his doctor because he's been having problems remembering things. After a battery of tests the doctor says, "Unfortunately, I have bad news, and I have very bad news."

"What's the very bad news?" the man asks warily.

"Well," says the doctor, "our tests show that you have cancer and only have three weeks to live."

"Oh, my God!" says the man. "Well, what's the bad news?"

"Our tests indicate that you also have Alzheimer's disease," says the doc.

"Well, I can always look on the bright side," says the man. "At least I don't have cancer!"

我實在看不到笑點在哪裡...

請大家可以詳細說明一下嗎?

謝謝.