Hi Kimberly
Yes probably finding out a bit more about the cause of the pain - although from what you describe it sounds like he developed neuropathic pain or causalgia (CRPS2).
the TENS may help but it probably is best if your friend's dad has been assessed by a multidisciplinary team. For example standard pain killers are not always the best medications for neuropathic pain. Drugs such as Neuroleptics and tricyclics given in the appropriate dosage for chronic pain often have a role on modulating the central nervous system. So he should be seen by a pain team: pain specialist + psychologist + physio - that is if he hasn't been seen already. Given his history of cancer it might be quite complex who is treating him. You could ask if he has been seen and what type of medications were given.
Kinberly the educator in me thinks that while your role here is more the concerned friend it is a great opportunity for you to find out more about this type of pain management and what you as a physio might be able to do. (Sorry I can't help it!). Here is a bit of reading you could do:
Assessment of neuropathic pain -- Callin and Bennett 8 (6): 210 -- Continuing Education in Anaesthesia, Critical Care & Pain
It is a recent guideline for the assessment of neuropathic pain.
And here is a Cochrane review on TENS for chronic pain:
http://www.mrw.interscience.wiley.co...222/frame.html
You should be able to get these through your institution but if you get stuck send me your email and I will forward them to you.