He took the pregnancy left in his medicine cabinet by an ex-girlfriend as a joke, but when the two pink lines appeared showing a positive result, the man — whose name has not been made public — was definitely surprised.

To note the bizarre occasion, a comic illustrating the event was drawn and posted on Reddit, where it attracted more than 1,300 comments in three days from knowledgeable and concerned viewers.

"You may have testicular cancer! Get to an oncologist, tell them you took a pregnancy test and it came out positive," one Redditor remarked.

Fortunately, the man heeded the advice — and a visit to the doctor revealed a small growth in the his right testicle.

Pregnancy tests do their magic by detecting beta human chorionic gonadotropin (hCG), a hormone produced in the placenta, but it's also a surprise ingredient in some cases of testicular cancer.

"It turns out a fair number of testicular cancers make the same exact hormone," said Dr. Mark Pomerantz, a genitourinary oncologist at the Dana-Farber Cancer Institute in Boston. "There are very few things in the body that produce beta hCG, and testicular cancer is one of them."

Following the story on the Reddit thread (like some kind of modern format soap opera), we find that the tumor was caught early, but surgical removal of the testicle may be required.

A positive pregnancy test suggesting testicular cancer is not a fluke, but the first sign is generally swelling or a lump.

"It's typically spotted by the guy himself," said Dr. Christopher Wood, professor and deputy chairman of urology at the University of Texas MD Anderson Cancer Center in Houston. "We recommend men do self-exams in the shower once a month to make sure there aren't any major changes."

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