Well personally I would have him put to sleep rather than put him through a very serious operation which no doubt will be painful and may only grant him a few weeks/months of life before he finally succumbs to cancer. If it is malignant then it has probably already spread to other parts of his body and I would be very concerned about his quality of life postoperatively. If the biopsy comes back and it is a malignant tumour would you have him put to sleep or let him carry on in pain until he dies? Sorry to be so blunt and I know it's very upsetting, but I think it's selfish to put a pig through such major surgery when the prognosis is so poor given the clinical observations to date.