Mistreatment
One suitable prefix for the word "treatment" is "mis-", which would change it to "mistreatment" to denote poor or unfair handling.
Cardio-, meaning heart, is the prefix of cardiology.
It means, literally, "in", as opposed to "out". It's not so much a prefix as a portmanteau word, combining the words in + patient.
The prefix be- indicates thoroughness or completion of treatment, as in bespeak or besiege, or an action that causes a condition to exist e.g. belittle, befriend, besmirch.
Mistreatment
Booking a hotel room with the prefix of "doctor" may sometimes lead to receiving special treatment or upgrades due to the assumption of higher status or importance.
The prefix anti- means against, so antitumor treatment is anything designed to fight the tumor, such as chemotherapy and radiation.
Prefix=IN
The prefix for inadequate is in-. The prefix in- means not.
The prefix for include is in-. This prefix means not.
Yes, prefix does have a prefix. The prefix is pur-.
Demi has no prefix; it IS a prefix.