Police say the victim was struck in the chest on a southbound 4 train.
It happened just before 3 a.m. Tuesday.
The man was taken off the train at the 138-St station and rushed to Lincoln Hospital.
The suspect in the stabbing ran away.
It was the second stabbing on the subway in 24 hours.
No arrests have been made.
This is a developing story. Check back for updates.
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