Follicular Thyroid Cancer
Follicular carcinomas are the second most common type of thyroid cancer. Follicular thyroid carcinoma (FTC) is a well-differentiated tumour and resembles the normal microscopic pattern of the thyroid.
FTC originates in follicular cells and is the second most common cancer of the thyroid, after papillary carcinoma. Follicular and papillary thyroid cancers are considered to be differentiated thyroid cancers; together they make up 95% of thyroid cancer cases. Papillary/follicular carcinoma must be considered a variant of papillary thyroid carcinoma (mixed form), and Hurthle cell carcinoma should be considered a variant of FTC.
Thyroid neoplasms arising from follicular cells (adenoma, carcinoma, and follicular/papillary carcinoma) show a broad range of overlapping clinical and cytologic features. A clear distinction between benign and malignant disease based solely on cytological examination of a needle biopsy specimen may be difficult. For this reason, a surgical procedure may be necessary to obtain sufficient tissue for a definitive diagnosis of follicular thyroid cancer. Pathological examination showing capsular or vascular invasion may be required for this determination/
Follicular Thyroid Cancer Diagnosis
- Fine-needle aspiration cytology (FNAC) of thyroid nodules has become the primary diagnostic test in the initial evaluation of thyroid nodules
- Management of thyroid nodules is based on correlating a specific cytologic reading with the probability of malignancy
- Two particular cytologic readings that lack accuracy are follicular neoplasms and cells that show atypia
- In most reported series, follicular neoplasms and cells showing atypia are included in a broad “suspicious” category, with reported overall malignancy rates generally between 20% and 30%
- Therefore patients with thyroid biopsy results that are read as ‘follicular neoplasms’ or with cells showing ‘atypia’ will likely need the nodule surgically removed with the whole lesion sent for accurate diagnosis by pathology
Features of Follicular Thyroid Cancer
The highest incidence of thyroid carcinomas in the world is among female Chinese residents of Hawaii. In Hawaii, incidence of FTC ranges from 10-30 new cases a year per million inhabitants.
Of all thyroid cancers, 17-20% are follicular. According to world epidemiologic data, follicular carcinoma is the second most common thyroid neoplasm. However, in some geographic areas FTC is the most common thyroid tumour. The relative incidence of follicular carcinoma is higher in areas of endemic goitre.
- Peak onset from age 40 to 60
- Females more commonly affected than males by 3 to 1 ratio
- The prognosis is directly related to the tumour size – with less than 1 centimetre tumours having a good prognosis
- They are rarely associated with radiation exposure
- Spread to lymph glands is uncommon (around 10%)
- Invasion into blood vessels within the thyroid gland is common
- Distant spread (to lungs or bones) is uncommon – but more common than with papillary thyroid cancer
- Many cases of FTC are subclinical and the most common presentation of thyroid cancer is an asymptomatic thyroid mass, or a nodule, that can be felt in the neck
- A medical history will identify any risk factors or symptoms – for any patient with a lump in the thyroid that has appeared recently, a history regarding prior exposure to radiation is relevant along with a family history of thyroid cancer
- Some patients have persistent cough, difficulty breathing, or difficulty swallowing. Pain seldom is an early warning sign of thyroid cancer
- Other symptoms (eg, pain, stridor, vocal cord paralysis, hemoptysis, rapid enlargement) are rare – these symptoms can be caused by less serious problems
- At diagnosis, 10-15% of patients may have distant metastases to bone and lung and initially are evaluated for pulmonary or osteoarticular symptoms (eg, pathologic fracture, spontaneous fracture)
- The diagnosis of follicular thyroid cancer is usually only made after the operation, when the pathologist can thoroughly inspect and examine multiple portions of the thyroid nodule under the microscope
- Patients with thyroid cancer on the final pathology will require that the rest of their thyroid be removed in an operation called a “completion thyroidectomy”
- Your surgeon will usually use the same incision and you can expect the recovery to be similar to the recovery after the initial operation
Despite its well-differentiated characteristics, follicular carcinoma may be overtly or minimally invasive. Patients with minimally invasive disease have an excellent prognosis with a limited need for lymph node removal surgery.
However, FTC tumours may spread to other organs. Life expectancy of affected patients is related to their age; the prognosis is better for younger patients than for those who are older than 45 years. Patients with FTC are more likely to develop lung and bone metastases than patients with papillary thyroid cancer.
- Pathology is key in predicting survival
- The overall cure rate is around 95% for younger patients with small lesions
- Tumours with microscopic capsular or venous capsular invasion have cure rates in the 99% range
- Larger tumours that can be recognized by the surgeon have a 10 year cure rate in the 40% range
- The Hurthle cell variant of follicular or papillary cancer do not concentrate radioactive iodine very well (if at all) and are more likely to metastasize (spread) to other parts of the thyroid and to lymph nodes
If you have any questions about thyroid symptoms or thyroid surgery, you should speak to your local doctor, who will arrange to contact your thyroid surgeon.