The victim was on a train in the 4100-block of West Irving Park Road at about 2:30 a.m. when police said he became involved in a verbal altercation with a 30-year-old man.
The younger man took out a sharp object and tried to stab the victim, who reached for the object to try to disarm and became injured on his hand, police said.
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The injured man was transported to Swedish Hospital in good condition. The suspect was arrested without incident and charges are pending, police said.