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 tumours that are on the borderline between benign and malignant (cancerous). Often, the definitive diagnosis of the type and sub-type 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 sub-types 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 sub-types of PTC.
Classical variant, also known as conventional variant, is the most common sub-type 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 favourable outcomes. The tall cell variant is characterised by a predominance of tall columnar tumour 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 characterised by mostly “column like” cells. These tumours also have a higher risk of spread to the rest of the body.
- Diffuse Sclerosing Variant
Diffuse sclerosing variant of papillary thyroid carcinoma is characterised 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 analysed 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 tumour 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 tumours. This variant is associated with a more aggressive behaviour overall.