もし後に英小文字がもっと続く場合でも先頭10桁をマッチさせたい
(AAAaaaaaaaaaaaaaaaaaaaaaaとかでも先頭10桁をとる)場合
(?<=^|[^A-Z])(?=[A-Za-z]{10}([A-Za-z]*)(?:[^A-Za-z]|$))[A-Z]+[a-z]+(?=\1(?:[^A-Za-z]|$))