The most common and most likely answer to this crossword clue is the 9 letter word TREATABLE
I've seen this crossword clue in The Times
T
R
E
A
T
A
B
L
E
More clues leading to the result TREATABLE
Buddy explains!

The straight part
We know that "As many illnesses are" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as many illnesses are = treatable.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TREATABLE mean?
TREATABLE adjective- Able to be treated; not incurable.
- Not intractable; moderate.