"Life, like swimming the 100 free, can come at you hard and fast as you cant always see who, or what, may be chasing you down," he wrote in the Thursday post. "Recently, I went to the doctor as something didnt seem quite right. At the very least, I still needed to get my flu shot so it couldnt hurt. After a few tests and visits with a specialist, I unfortunately learned that I have Testicular Cancer."

The prognosis is good: Adrian said they caught it early, and he's already started treatment. In fact, it won't be long before the swimmer is back to his regular routine: "I will be back in the water in a few short weeks with my sights fully set on Tokyo!"

View this post on Instagram Life, like swimming the 100 free, can come at you hard and fast as you cant always see who, or what, may be chasing you down. Recently, I went to the doctor as something didnt seem quite right. At the very least, I still needed to get my flu shot so it couldnt hurt. After a few tests and visits with a specialist, I unfortunately learned that I have Testicular Cancer. On the bright side, we caught it early, I have already started treatment and the prognosis is good. I will be back in the water in a few short weeks with my sights fully set on Tokyo! Along the way, I hope to share my journey in an effort to help break the stigma of discussing mens health issues. Ive realized that too often we tend to avoid these important topics, ignore the potential warning signs, and put off getting the medical help that we may need. As I told my family, Ill be putting my public health degree to work a little sooner than I planned! But in all seriousness, I am keeping a positive attitude as cases such as mine are curable. I am extremely grateful for my family and friends, especially my wife, for their love and support. I am scheduled for surgery early next week and will provide an update soon. #menshealth #testicularcancer #standuptocancer A post shared by Nathan Adrian (@nathangadrian) on Jan 24, 2019 at 12:20pm PST

As Adrian embarks on his medical journey, he wants to encourage guys to speak up when their bodies don't feel quite right.

"Ive realized that too often we tend to avoid these important topics, ignore the potential warning signs, and put off getting the medical help that we may need," he wrote. "As I told my family, Ill be putting my public health degree to work a little sooner than I planned!

"But in all seriousness, I am keeping a positive attitude as cases such as mine are curable. I am extremely grateful for my family and friends, especially my wife, for their love and support. I am scheduled for surgery early next week and will provide an update soon."

Every year, roughly 9,500 cases of testicular cancer are diagnosed in the U.S. The average age of diagnosis is 33.

How can you spot it? Besides the most common sign-a lump in the testicle- symptoms of testicular cancer include a heavy feeling in the belly, a change in the size of your testicle, swollen legs, tender breast tissue, and lower back pain.

Testicular cancer is very treatable. Timothy Gilligan, M.D., a testicular cancer medical oncologist at Cleveland Clinic, previously told Men's Health that "for every 100 men diagnosed with testicular cancer, 96 are cured."