Follicular thyroid cancer is the second most common type of thyroid carcinoma. Although this tumor is well differentiated, it grows invasively and tends to form metastases.
Local mass effects are the most frequent complications of FTC, since these tumors generally don't produce thyroid hormones. Consequently, patients present with an asymmetric, palpable mass below the larynx. Due to its close proximity to the latter, patients may be hoarse or dysphonic. They may also claim difficulties while ingesting solid food, less often while swallowing water. Dysphagia may be accompanied by dyspnea. If the tumor exerts pressure on the recurrent laryngeal nerve, the aforementioned symptoms tend to aggravate and the affected person may claim cough. FTC are usually not painful and grow slowly.
Anamnesis and physical examination should address the following issues:
FTC patients may present metastases at the time of initial presentation. In some cases, symptoms triggered by functional impairment of lung, liver or bones may dominate the clinical picture. In this context, intolerance to exercise, upper abdominal pain, jaundice and pathologic fractures may be registered.
Workup should aim at tumor staging and grading. Precise localization and size of the primary tumor can be evaluated sonographically. In general, FTC are solitary tumors that don't invade the capsule of thyroid lobes. In order to detect metastases, patients may be submitted to scintigraphic examination. Because this technique is based on enrichment of thyroid-like tissue with radio-labeled iodine, its sensitivity is rather low in case of carcinomas that don't produce thyroid hormones. Here, magnetic resonance imaging or computed tomography scans are indicated . About 10% of FTC patients present metastases at the time of first diagnosis.
Histopathological analysis of tissue samples is required to determine whether a thyroid tumor is benign or malignant, if it is indeed an FTC, and if the latter grows minimally or widely invasive. Although examination of fine needle aspirates may yield important information to this end - nuclear morphology, for instance, may reveal PTC - more extensive tissue samples are often required for a precise diagnosis and prognosis. As has been indicated above, differentiation between minimally or widely invasive growth of FTC may be particularly complicated. Therefore, surgical removal of neoplastic tissue is sometimes applied as a therapeutic and diagnostic measure, since conclusive results can much more easily be provided upon analysis of resected tissue.
Furthermore, serum concentrations of thyroid stimulating hormone (TSH), thyroglobulin, thyroxine (T4) and triiodothyronine (T3) should be measured. Hormone-producing thyroid cancer is associated with increased levels of thyroglobulin, T4 and T3, but concentrations of TSH are reduced due to autonomous activity. The latter may be confirmed by TSH suppression tests, but false-negative results are likely. A significant share of hormone-producing thyroid carcinomas does respond to TSH suppression. It has to be noted that these are not exclusion criteria for FTC, since this type of carcinoma most often does not produce thyroid hormones.
Evaluation of calcitonin and calcium levels is recommended and is particularly useful to differentiate FTC and MTC.
Surgical resection is the treatment of choice, but recommendations regarding the extent of tissue removal vary.
Some experts advise to limit surgery to lobectomy and isthmusectomy, unless widely invasive FTC has been diagnosed previously . Due to the aforementioned limitations of histopathological analysis of fine needle aspirates, this is rarely the case. Here, determination of the subtype of FTC is realized after surgery and only if a high degree of invasiveness is detected will the remaining part of the thyroid gland be removed. On the other hand, total thyroidectomy may be indicated for all patients diagnosed with FTC . This approach is justified by the fact that the majority of FTC patients do indeed suffer from widely invasive FTC and that this type of thyroid carcinoma is likely to metastasize early.
In any case, total thyroidectomy should be realized if the primary tumor measures more than 1 cm in diameter, if both lobes are affected, if invasive growth has been confirmed, if any metastasis has been detected, and if the patient is older than 40 years. Neck dissection and removal of lymph nodes as well as additional surgical procedures to resect metastases in internal organs may become necessary in such cases, too.
Post-surgical substitution of thyroid hormones is required.
Subsequently, patients should undergo radioactive iodine therapy to destroy possibly remaining tumor cells in the thyroid gland and in metastasis.
Prognosis of FTC is guarded since the disease is related to a mortality of 10-15%. Unfavorable prognostic factors are age over 45 years, size of the primary tumor over 2.5 cm in diameter, widely invasive FTC and histopathological anomalies as well as presence of metastases at the time of diagnosis .
The etiology of FTC is only partially understood. And although a variety of risk factors for thyroid cancer have been identified, most of them are primarily associated with PTC. Of course, it has to be assumed that both types of differentiated thyroid carcinoma share some causative factors. Little is known about specific triggers of FTC, though.
In general, thyroid cancer is a rare disease. However, malignancies of the thyroid gland are the most common type of cancer that affects endocrine glands. Its annual incidence doesn't exceed 3 per 100,000 inhabitants, whereby less than 1 per 100,000 people are diagnosed with FTC. Retrospective analyses have shown a reduction of FTC incidence due to less frequent iodine deficiency, followed by a renewed increase of case numbers. The latter is generally ascribed to improved diagnostics.
Women are diagnosed with FTC up to four times more often than men.
FTC may develop at any age.
FTC usually develop as solitary tumors that cause local mass effects but that most often don't produce thyroid hormones. And while the thyroid gland consists of two connected lobes, both of which are surrounded by capsules consisting of taut connective tissue, most FTC are restricted to a single lobe and don't invade the capsule. FTC may be delimited by a pseudocapsule, but may still invade blood or lymphatic vessels. Thus, minimally invasive FTC and widely invasive FTC should be distinguished histopathologically, whereby the latter is more frequently observed. Unfortunately, even though the outcome may depend on invasiveness, clear diagnostic criteria for either type of FTC are not available .
According to the above described risk factors for FTC, the following measures may diminish the individual risk to develop this disease:
Thyroid cancer is a rather common type of malignant neoplasia, but benign tumors of the thyroid gland are more often observed.
Thyroid neoplasms may originate from distinct cell types, form well-demarcated tumors or grow invasively, and are thus associated with different outcomes. Generally, the following types of thyroid carcinoma are distinguished :
The thyroid gland is located in the neck, below the larynx. It consists of two lobes that are connected by an isthmus. Thyroid tumors usually manifest in form of a palpable, firm, painless mass. Most of these tumors are benign, but malignant degeneration of thyroid cells may also occur. Dependent on the precise origin of such a malignant tumor, several types of thyroid cancer are distinguished. Follicular thyroid carcinoma (FTC) is the second most common one, with papillary thyroid carcinoma being the only type of thyroid cancer that is more frequently diagnosed.
Although FTC are generally well differentiated, they may grow invasively and form metastases in distant organs, namely in lung, liver and bones. An early diagnosis facilitates treatment and reduces the likelihood of metastatic spread. Thus, any mass suspicious of thyroid cancer should be thoroughly examined. Patients who suffer from thyroid cancer like FTC often claim difficulties while swallowing and breathing. Hoarseness and persistent cough may also be noted.
Diagnostic imaging techniques such as sonography and scintigraphy, in some cases also magnetic resonance imaging or computed tomography should be applied to assess localization and size of the primary tumor and to revise the whole body for possible metastases.
According to the results of these test, therapy will be planned: Thyroid cancer requires surgical removal of degenerated tissue. In order to avoid recurrence, the whole thyroid gland is removed in many cases. If metastases have been detected, further surgical interventions may become necessary.
Patients who underwent thyroidectomy need to replace thyroid hormones by medication.