hi, my golden retriever is 5 years old now and he's been eating his back, he acualy eats it open, he's also been losing weight,i've also found a lump on his left back leg, it's round and hard but still firm, id this cancer?? the lump was there before, in the same spot, but it went away but now it's back again? if it is cancer, any idea what kind? before i bring him to the vet. my vets on vacation. thanks soo much for your help

