Dan,
This is a real sensitive, personal area, and so you will likely get lots of opinions on this.
Consider this...if you were female and having surgery on reproductive parts, you wouldn't describe the details either. What would a woman write in a similar situation? A sentence something like this might be appropriate: "I am taking a brief time off from work to address and recover from an important health concern. I would like to thank you in advance for your best wishes. We will be unavailable only for a short time (2 weeks), and look forward to returning to full service by mid-June."
Personally, I wouldn't lie. Some customers might ask you, on an individual level, after your email is sent which you may choose to answer one-on-one, others will have the courtesy to not ask.
Totally different thought...
You have a tiny amount of cancer found. Why not postpone surgery 3 months, and get off-peak? You have no need to rush.
Post Edited (Casey59) : 5/18/2010 8:17:18 AM (GMT-6)