SQL & PL/SQL

I saw this code in one of the procedures we are using ... is it possible to avoid EXIST caluse:

update table_x p
set p.internal_issue_ky = (select sh.internal_issue_ky
from security_history sh, XT_SECURITY xs
where sh.internal_wins_issue_id = xs.internal_wins_issue_id
and sh.as_of_dt = xs.as_of_date
and p.internal_wins_issue_id = sh.internal_wins_issue_id
and p.effective_dt between sh.as_of_dt and sh.next_as_of_dt
)
where exists
(select sh.internal_issue_ky
from security_history sh, XT_SECURITY xs
where sh.internal_wins_issue_id = xs.internal_wins_issue_id
and sh.as_of_dt = xs.as_of_date
and p.internal_wins_issue_id = sh.internal_wins_issue_id
and p.effective_dt between sh.as_of_dt and sh.next_as_of_dt
)


Thanks.