It happened around 3:45 p.m. on SEPTA's eastbound Market-Frankford Line platform near 40th and Market streets.
According to SEPTA, an altercation led to the stabbing of a man in his 20s.
He was taken to an area hospital for non-life-threatening injuries.
No arrests have been made.
Anyone with information is asked to call police at 215-686-TIPS.
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