Dog possible cancer possible cyst please help

[Milesaldo7]

Hello.I am new here and I joined this forum to learn share and be helpful from my own personal experiences.My name is joey ,I hope this forum us active .anyway I have a 11 year old pit bull boarder collie mix some say he could be mastiff because his great sized head. He has lumps and bumps on his body I've always taken the best care of him since he was a baby always fed him low fat diet. On his chest he had a gulf ball size fatty cyst and below that he has a large very pink cyst type thing looks like an in large nipple this is the size of a small round bubble gum now it's almost golf ball sized and it leaking a little puss I need to know what it is