A funny post on the popular social news site Reddit soon turned into a serious health issue regarding cancer – and may have saved one man’s life, the San Francisco Chronicle reported.

An anonymous user posted a story about his friend, who jokingly took a pregnancy test left by an ex-girlfriend and was surprised when the test came back positive. Thousands of Reddit users posted comments on the story, many telling the original user to have his friend get tested for testicular cancer.

Pregnancy tests detect the amount of the hormone beta human chorionic gonadotropin (hCG) in an individual’s urine. While the hormone is produced by the developing placenta during pregnancy, it can also be associated with testicular cancer, according to the National Institutes of Health.

Eventually, the user posted a second post to Reddit, saying his unnamed friend went to the doctor and did indeed have a small testicular tumor. According to the user, the tumor is easily treatable since it was found early.

Click for more from the San Francisco Chronicle.