This is gonna hit you right in the feels ...
Steelers RB James Conner -- who famously battled cancer in college -- went out of his way Sunday to comfort another man fighting the illness ... and the whole thing is insanely emotional.
The fan in the "FcukCancer" jersey is Richie Marsili -- who was diagnosed with a rare untreatable sarcoma and had always wanted to get on the field for a Steelers game.
Richie's friend Rusty Sergent made it all happen -- buying tickets and field passes and tweeting at Conner in the hopes the NFL star could "see him and give some encouragement.