Excerpt from UCSF Endocrine Surgery...
"Goiter can be the result of thyroid tumors, which are usually benign, but sometimes malignant. Most thyroid tumors present as discrete nodules, but there are several kinds of thyroid cancer that can cause generalized swelling of the gland. These include infiltrating papillary thyroid cancer, lymphoma, and anaplastic thyroid cancer. Certain facts make it important to consider the possibility that a goiter might be malignant.
These include one or more of the following symptoms: rapid enlargement of a goiter over a few weeks, the onset of new thyroid-related pain, difficulty swallowing, shortness of breath, or coughing up blood; or a goiter in someone with risk factors for thyroid cancer, such as a person who had childhood radiation to their neck or who has a close relative with thyroid cancer."