 In 1888 Keen also performed one of the first successful removals of a brain tumor.Keen was the leader of a team of five that performed a secret surgical operation to remove a cancerous jaw tumor on Grover Cleveland in 1893 aboard Elias Cornelius Benedict's yacht "Utowana".Keen and four assisting doctors made their way to the yacht by boat from separate points in New York with Cleveland and Bryant boarding in the evening for the night aboard before sailing the next morning.