What Causes Painfull White Growth Between The Buttocks?

This pain is between the cheeks of his butMy husband had a pilonidal cyst surgery about 15 years ago and is now experienceing some kind of pain,white matter,but I really can't see a cyst but he is quiet miserabe. Can you give me any idea? He is also being treated for advanced prostate cancer so anything like this always draws suspicion.