Subcutaneous cyst/growth eruptions in 12yr old mixed male Spaniel
 

12 year old mixed spaniel has developed problem where subcutaneous cyst-like structures, which were dormant for most of his life, have begun to erupt through the surface of the skin. Largest one under left forepaw/arm area, about the size of a baseball, had to be surgically removed twice - re-erupted some 5 months after initial removal. The 6 or so that have erupted since on left hind leg, top of spine, right upper foreleg and upper right chest area have simply bled out/drained and scabbed over.
Beside surgical removal, one vet tried cortisone shot (4 injections) around base of the large-marble sized one on left hind leg which had erupted through the skip and that appeared to reduce the swelling and weeping/bleeding for about a week with it being somewhat weepy now but not erupting with blood and fluid.
What is this and what can be done for this poor fellow? I've been using Sulfodene antibiotic salve/ointment on them as much as the dog will permit and can not lick off; but I'm afraid with the warmer weather coming that the insects will be attracted to those that I can't cover with a tee-shirt or that the dog won't lick off the medicine.
Thanks,
Greynold99