Yes you can prune it back - but if its outside, not before mid April/May, depending on temperature. Keep it somewhere sheltered or inside anyway till then - they're a bit tender.

Wear gloves and be careful to wash your hands afterwards as this is a poisonous plant. Dispose of the bits carefully too.

I have one in my front garden and i did this about a year ago and it looked much better for it.
I didn't get any reaction on my hands though and i wasn't careful when i was working on it, perhaps it's just if you're a 'sensitive' person.

You were lucky then Louise.....it really is very poisonous....you probably washed your hands after dealing with it.....

I've not had a problem with sap from this either - maybe I just didn't get any on me, though I'm sure I must have done at some point.