Is there a moral difference between withholding truth from someone and lying to someone?

What I'm talking about is: keeping a secret vs. lying. The former is to knowingly withhold truth, and the latter is knowingly telling a falsehood.

Most people view keeping a secret morally permissible (a right to privacy), while condemning lying as morally wrong (no right to deception).

However, in some cases, if one wants to keep a secret, one must lie.

Example:

Case of withholding information:

Suppose that a man is diagnosed with cancer. He does not want his family to worry, so he does not tell anyone that he is diagnosed with cancer, and asks that his healthcare providers keep his diagnosis confidential.

Case of deception:

Suppose that in our above example, the man's wife learns of his visit to the doctor. She asks him if anything is wrong. He tells her that everything is fine. He knows that if he didn't lie to her (i.e. if he had refused to answer the question) that she would have inferred that something was wrong, and persisted in trying to find out what that was, while worrying about it the whole time.

So, do you think that there is a moral difference between knowingly withholding truth and knowingly telling a lie?

What if telling a lie is necessary to help one withhold truth?