A man refuses treatment for a potentially life-threatening condition. What are the ethical issues involved?

When answering an ethical dilema such as this one, you must always follow the four key principles of medical ethics: autonomy, non-maleficence, justice and beneficience. 

Autonomy (A) = this forms the basis for "informed consent". That is that a competent adult (or young person potentially) has the right to make informed decisions about their own healthcare.

Non-malefience (NM)= Do no harm. Obligation to do no harm intentionally. 

Justice (J) = Moral question of healthcare equality. Fair distribution of resources, competing needs, rights and obligations.

Beneficence (B) = Welfare of patient should always be first priority.

Now it is easy to see how you could answer this interview question:

A = If the "man" in question is competent and fully informed of his options then he has the right to decide to refuse treatment.

NM = Could treatment do more harm than good?

J = Is it fair for him to refuse treatment? Does he have a family?

B = Must act in the patients best interests. In this case, the role of the doctor would be to advise treatment in the strongest way possible.