Type
First, it is important to remember that not all lumps and lesions in the neck are cancer. Some nodules are benign (non-cancerous), and there are some tumors that are on the borderline between benign and malignant (cancerous). Often, the definitive diagnosis of the type and subtype of cancer is not fully determined until after the thyroid is removed. This is because the pathologist sometimes needs to see the entire nodule within the thyroid gland before being able to determine if the nodule is benign or malignant.
There are a few different types of well-differentiated thyroid cancers, as well as a few subtypes or variants within each type.
Papillary Thyroid Cancer
Papillary thyroid cancer (PTC) is the most common form of differentiated thyroid cancer, representing approximately 85% of cancers of the thyroid gland. There are several different subtypes of PTC.
- Classical
Classical variant, also known as conventional variant, is the most common subtype of papillary thyroid cancer. Approximately half of all papillary thyroid cancers are classical variant. These cells have finger-like projections and contain enlarged, overlapping nuclei. This variant of papillary thyroid cancer grows slowly and has an excellent prognosis. - Follicular Variant
Follicular variant is the second most common variant of papillary thyroid cancer, and has a prognosis similar to that of classical variant papillary thyroid cancer. Follicular variant cells have features that resemble both papillary and follicular thyroid cancer cells. However, these cells do not have papilla (finger-like projections), and typically grow in clusters. - Tall Cell Variant
Tall cell variant is a sub-type of papillary thyroid cancer that is associated with less favorable outcomes. The tall cell variant is characterized by a predominance of tall columnar tumor cells whose height is at least 3 times their width. These tumors often present in individuals that are of older age and at a more advanced stage than classic papillary carcinoma. - Hobnail Variant
Hobnail variant of papillary thyroid carcinoma is rare and described by a specific “hobnail” appearance of the cells. This type is known to often spread to the rest of the body, especially the lungs, and has a worse prognosis than classic papillary carcinoma. - Columnar Cell Variant
Columnar cell variant of papillary thyroid carcinoma is characterized by mostly “column like” cells. These tumors also have a higher risk of spread to the rest of the body. - Diffuse Sclerosing Variant
Diffuse sclerosing variant of papillary thyroid carcinoma is characterized by widespread involvement of the thyroid gland and is more likely to spread to lymph nodes in the neck and to the rest of the body. Patients with this type of cancer do slightly worse than those with classic papillary carcinoma; however, response to treatment is generally excellent.
Follicular Thyroid Cancer
This is another well-differentiated thyroid cancer. It is the second most common form of thyroid cancer, after papillary thyroid cancer, representing approximately 12% of cancers of the thyroid gland. The diagnosis of follicular thyroid carcinoma can really only be made after the gland (or at least half of the gland) is analyzed under a microscope. The diagnosis is made when follicular cells are seen invading through the cover (capsule) of the nodule or into blood vessels. If this is not seen, then it is considered a benign (non-cancerous) follicular tumor called “non-invasive follicular thyroid neoplasm.”
Hurthle Cell Carcinoma
This is a variant of follicular thyroid cancer. When observed under the microscope, these cells have a different appearance than other follicular tumors. This variant is associated with a more aggressive behavior overall.
Grade
The grade of a cancer is usually only determined after the tumor has been removed and examined by a pathologist. The grade of cancer relates to how healthy or unhealthy the cells look under a microscope. In other words, a pathologist will determine the grade of cancer by comparing the amount of the healthy-looking tissue to the amount of cancerous tissue. If most of the tumor cells look like normal tissue, then the cancer is “well-differentiated” or “low-grade.” However, if the tumor cells look very different from normal tissue, then the cancer is considered “poorly-differentiated”, “undifferentiated”, or “high-grade.” The grade of the cancer may help to predict how quickly the cancer may spread.
The focus of this section is on well-differentiated thyroid cancers, which are, by definition, considered to be of a lower grade. However, some “well-differentiated” thyroid cancers may have portions that are “poorly differentiated.” Adjustments to postoperative treatment may be made if this is found on final pathology. Overall, this is an uncommon scenario.
Stage
The stage of a cancer is determined by the TNM staging system:
- The ‘T’ stands for tumor size.
- The ‘N’ stands for lymph node involvement.
- The ‘M’ stands for distant metastases, or cancer spread to other areas of the body.
Staging helps doctors determine how serious the cancer is and how best to treat it. For well-differentiated thyroid cancers (such as papillary thyroid carcinoma and follicular thyroid carcinoma), the staging is determined based on the patient’s age, with different staging systems for patients under and over 55 years of age.
Staging is generally based on the American Joint Committee on Cancer (AJCC) 8th edition guidelines. To learn more, see the AJCC TNM Staging Table and the TNM Staging Tool below.
TNM Staging Table, from the American Joint Committee on Cancer (AJCC)
| Age | T | N | M | Stage |
| < 55 | Any T | Any N | M0 | I |
| < 55 | Any T | Any N | M1 | II |
| ≥ 55 | T1/T2 | N0/NX | M0 | I |
| ≥ 55 | T1/T2 | N1a/N1b | M0 | II |
| ≥ 55 | T3a/T3b | Any N | M0 | II |
| ≥ 55 | T4a | Any N | M0 | III |
| ≥ 55 | T4b | Any N | M0 | IVA |
| ≥ 55 | Any T | Any N | M1 | IVB |
