If the lump on the throat is confirmed as mast cell, and if there is evidence of metastasis you should inquire about Chemo. Without looking it up believe Vincristine+Cytoxin are the drugs of choice. Regardless whether Chemo is an option or not for you, if mast cell is confirmed, then start giving the dog benedryl daily. Anti-histamines are thought to slow down mast cell cancer. At the very least they will make the dog feel better (e.g. mast cells release histamine).