gland, represents approximately 3% of thyroid cancers
and is often associated with multiple endocrine neoplasia
2. Medullary carcinoma produces excess calcitonin,
which makes it a useful tumor marker.5,8
Anaplastic thyroid carcinoma represents approximately
2% of thyroid cancers and is the most dangerous
form of thyroid cancer, because it metastasizes early to
the surrounding lymph nodes and distant sites.11 Other
thyroid malignancies, such as lymphoma and variants of
the 4 types mentioned above, make up the remaining
thyroid cancers. Clinically, thyroid cancer has been divided
into 2 categories: (1) well-differentiated, including
papillary and follicular cancers, and (2) poorly differentiated,
including medullary and anaplastic cancers.
After a diagnosis of thyroid cancer, it is important
to perform preoperative staging and imaging, because
it can alter the patient’s prognosis and treatment
course. Up to 50% of patients with differentiated thyroid
cancer will have cervical lymph node involvement,
despite the primary tumor size.5
Thus, a preoperative
neck ultrasound for contralateral lobe and
cervical lymph nodes is recommended for all patients
undergoing thyroidectomy for malignancy, to help
identify possible metastasis; however, neck ultrasounds
only identify 50% of the lymph nodes that are
found during surgery.5
Lymph node metastasis can be confirmed by ultrasound-guided
FNA on abnormal lymph nodes and/or
the measurement of thyroglobulin in the needle washout
if it would change the disease management.5
These
results are then used to stage the extent of the cancer.
The American Joint Committee on Cancer (AJCC)
has designated thyroid cancer staging by the Tumor,
Node, Metastasis (TNM) classification system.8
The
AJCC’s TNM classification system is available online
(at the AJCC website).8
In addition, thyroid cancer can be stages, using stages
I to IV, with the TNM classification system based on
the tumor type of thyroid cancer