I am so sorry to hear about your dog!
If it is indeed a thyroid adenocarcinoma than prognosis will depend upon if it has or has not metastasized.
Since it has not been diagnosed yet, your vet will probably perform a fine needle aspirate or biopsy of the mass. If the biopsy returns as positive for thyroid adenocarcinoma your vet will probably check for metastasis to the lungs and other parts of the body. Common metastasis sites include the lungs, the tissues of the throat, such as the larynx, the esophagus and by extension the abdomen.
The next step is surgical resection or excision of the tumor or tumors (usually only one lobe of the thyroid is affected). The best response after surgical removal is achieved if the mass is freely movable, small (less than 4 cm=a bit less than 2 inches), and of course if there is no metastasis. You said that the mass is currently the size of a lemon, so we are already at the two inch mark, however the mass may be considerably smaller when you take away the size of the peri-thyroid fat, fascia and skin.
If the mass has metastasized, Radiation therapy utilizing Iodine 131 may be necessary, along with chemotherapy.
The survival rate can be up to 3 years if only Western Medical therapies is used. Occasionally It can be longer with the additional use of some alternative medicine modalities, but only occasionally. No single therapy is a panacea for cancer.
We just found out that she has lymphosarcoma and she has swollen lymph nodes all over her body, not just the large one we noticed in her neck. We are going to speak with an oncologist either tomorrow or the next day regarding chemotherapy. What are some alternative medicine treatments that can be used in conjunction? I read about fish oil and using a higher meat diet. What are some other supplements that can be used? We are willing to try anything.