I too was diagnosed with Squamous cell carcinoma of the anus about 8 years ago ... I was given radio and chemotherapy, but unfortunately the tumour returned within 2 years, so I then needed an op for complete removal of my rectum.  I have now been given the all clear, but since my treatment I too suffer from the most painful cramp, starting in my right groin and going down the inside of my thigh to my knee.  This usually comes on at night as I attempt to turn over, but have been known for it  to start just lounging in the chair and crossing one leg over the other. The following day, the pain continues as if I have a pulled muscle. 

I do 4 dance classes a week and notice that my right hip is much tighter than my left, so can only conclude that it was either the treatment, or the operation that has caused this. 

Not sure if it was a coincidence the drinking tonic water during the episode (after walking down the stairs) eased it, or perhaps it was just the walk down the stairs ;) 

Very interested to read that someone else seems to be having the same problems ... 

Been suffering  since my treatment  chemo and radiotherapy  for the past 4 years started with the feet always so hot and burning  this continued  to a feeling something  is moving around in my bones in my legs and now this has moved to my hip currently  I'm at a loss and made to feel that I should  be grateful  I'm alive. I go swimming and rowing machine try cycling  all at the gym walk 2 miles a day to work and back have to do this all to music otherwise it's not possible on the weekend I collapse in a whole world of pain I'm at a loss as to what else I can do 

If anyone has any suggestions  please