Cade Horton is just the ninth Cubs starter since 1901 to leave a game after pitching exactly five hitless innings. The previous one was Jon Lester, on July 27, 2020, at Cincinnati. The Cubs wound up winning that game, 8-7.
The only other one this century was Matt Clement, on Sept. 10, 2003, at Montreal. He gave up three unearned runs, as he walked five, and the Cubs eventually lost, 8-4.
The others:
Lon Warneke, 1943, at Philadelphia (Cubs lost, 4-3)
Bob Schultz, 1951, at St. Louis (Cubs won, 10-5)
Howie Pollet, 1953, at Cincinnati (Cubs lost, 7-4)
Don Elston, 1960, at home vs. Giants (Game ended in 1-1 tie after 14 innings)
Ray Newman, 1971, at home vs. Expos (Cubs won, 8-4)
Bill Caudill, 1980, at Pittsburgh (Cubs lost, 5-4, in 20 innings!)