Emily –

I understand and agree that you need to put your chemo
first.  This is about your life and your
health.

That said, I think you could respond comfortably to the
question about a start date by providing a specific date such as Monday August
20^th or August 22^nd, whatever makes sense depending on
what you have been told by your Oncologist about the effect of this round of
chemo. 

 Tell your potential employer that you made a commitment before
the telephone interview and that you need to support that commitment.  This will give them a bit more information
than “a personal issue” and it will reinforce that you have a sense of loyalty
and strong ethics. It is also the truth, without revealing too much. If you
have to give more details you can also add that it has something to do with a health
issue in your family. Hopefully, you don’t have to expand on your explanation.

 If your interview is this Thursday, it is somewhat presumptuous
of any employer to assume that you could start within one workday of an
offer.  After all, it probably took them
a great deal longer to respond to your application and schedule your telephone screening
and your interview.

 If on your start date, you are feeling poorly, you are
better not reporting to work, because you won’t create a good first impression.  Call in, apologize profusely and tell them
that you are not feeling well, that you are not sure why and that you will plan
to be there the following day.

 I am sure that you are excited about the prospect of this
new internship.  Verbalize that
enthusiasm to the potential employer, assure them that you are delighted with
the offer and that you feel confident that you can make a significant
contribution; don’t feel guilty about not being able to show up immediately for
the new job.

 I hope this helps.

 Margot

Thank you for your response! Your answer sounds just right to me.