Histological Features
Under the microscope, FTC is characterized by its growth pattern, which may include microfollicular, normofollicular, or macrofollicular structures. Unlike other thyroid carcinomas, FTC lacks the papillary structures seen in
papillary thyroid carcinoma. The tumor cells often exhibit a uniform appearance, with small to medium-sized nuclei and moderate amounts of eosinophilic cytoplasm.
Capsular and Vascular Invasion
A key diagnostic feature of FTC is its potential for capsular and
vascular invasion. Capsular invasion is identified when tumor cells penetrate the fibrous capsule surrounding the thyroid gland. Vascular invasion, on the other hand, is noted when tumor cells are found within blood vessels, which indicates a higher risk for metastasis.
Immunohistochemistry
Immunohistochemistry plays a crucial role in diagnosing FTC. Common markers include thyroglobulin, TTF-1, and PAX8, which are typically positive in follicular cells. Additionally, markers such as galectin-3, HBME-1, and cytokeratin 19 may be used to differentiate FTC from benign follicular lesions.
Genetic Alterations
FTC is often associated with specific genetic mutations. The
RAS gene mutations and PAX8-PPARγ rearrangements are commonly observed in these tumors. These genetic alterations can be detected through molecular testing, which aids in the diagnosis and understanding of the tumor's behavior.
Diagnosis
The diagnosis of FTC is primarily based on histological examination. Fine-needle aspiration biopsy (FNAB) is a commonly used technique, but it may not always distinguish between benign and malignant follicular lesions. Therefore, a definitive diagnosis often requires a thorough histopathological evaluation of the resected tumor.Treatment
Treatment for FTC typically involves surgical resection of the thyroid gland, often followed by radioactive iodine therapy. The extent of surgery depends on the tumor's size, location, and extent of invasion. In cases of metastatic disease, targeted therapies and systemic treatments may be considered.Prognosis
The prognosis for FTC varies based on several factors, including the extent of capsular and vascular invasion, tumor size, and presence of metastasis. Generally, patients with minimally invasive FTC have a favorable prognosis, while those with widely invasive or metastatic disease may have a poorer outcome.Conclusion
Follicular thyroid carcinoma is a distinct type of thyroid cancer with unique histological and molecular characteristics. Understanding these features is essential for accurate diagnosis, effective treatment, and prognostication of this disease. Advances in
molecular pathology and immunohistochemistry continue to enhance our ability to diagnose and manage FTC effectively.
