In reply to mypyrex:
Depending on what treatment you had, you may find that you are slightly more susceptible to viral infections than you were. This shouldn't make much difference to getting out and about - just make sure that your vaccines are up to date. Most things you are likely to catch while trekking are bacterial anyway. It certainly shouldn't stop you doing what you want to do, and unless you are doing stupid stuff like preparing food without washing your hands (or at least using that gel on them) a couple of days without a shower should be no big deal.
Otherwise, you might find you are less fit and/or more lethargic. This will vary from person to person and only you can judge it. Just get back into things gradually - start with easy day trips and work back to the hut-to-hut treks.
Edited to add: if you really have concerns, speak to your consultant or GP. You may also find a support group to be helpful.
Post edited at 16:01