From the Guidelines
A Thy3f cytology in the thyroid could not be a papillary thyroid carcinoma, medullary thyroid carcinoma, anaplastic thyroid carcinoma, or lymphoma on final histology. The Thy3f classification specifically indicates a follicular-patterned lesion with architectural features suggesting a follicular neoplasm, as noted in the ESMO clinical practice guidelines for diagnosis, treatment, and follow-up of thyroid cancer 1. When a thyroid nodule is classified as Thy3f on cytology, it typically represents either a follicular adenoma (benign) or follicular carcinoma (malignant), with the distinction between these two entities requiring histological examination to identify capsular or vascular invasion, as outlined in the WHO criteria for the classification of thyroid tumors 1.
Some key points to consider in the diagnosis and management of thyroid nodules include:
- The diagnostic work-up of differentiated thyroid cancers (DTCs) comprises pre- and postoperative pathological and molecular assessments 1.
- Cytology findings are classified into diagnostic categories associated with different risks of malignancy, and most malignant thyroid tumors can be identified cytologically, although notable exceptions include follicular thyroid carcinomas (FTCs) and non-invasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTPs) 1.
- The WHO recommends reporting FTCs as ‘minimally invasive’ when capsular penetration is present without vascular involvement, and the terms ‘angioinvasive’ and ‘widely invasive’ should be reserved for follicular cancers with neoplastic emboli involving <4 or 4 blood vessels, respectively 1.
- Non-follicular malignancies like papillary carcinoma, medullary carcinoma, anaplastic carcinoma, and lymphoma have distinct cytological appearances that would typically result in different Thy classifications, and understanding these distinctions is important for appropriate surgical planning, as Thy3f lesions generally require diagnostic lobectomy to determine their true nature.
In terms of specific tumor types that could not be represented by a Thy3f cytology, these include:
- Papillary thyroid carcinoma, which is characterized by nuclear features rather than follicular architecture 1.
- Medullary thyroid carcinoma, which is derived from C-cells and has a distinct cytological appearance 1.
- Anaplastic thyroid carcinoma, which is highly undifferentiated and has a poor prognosis 1.
- Lymphoma, which is a non-epithelial malignancy and would not be classified as a thyroid neoplasm 1.
From the Research
Thy3f Cytology and Final Histology
- A thy3f cytology may not be malignant on final histology, as studies have shown that the risk of malignancy in thyroid nodules with THY3f cytology is around 17-20% 2, 3.
- The majority of patients with THY3f cytology may have benign lesions, such as follicular adenomas or multinodular goiter, on final histology 4.
- Some studies have reported lower malignancy rates for THY3f nodules, ranging from 11% to 17.9% 3, 5.
- The final histology for a thy3f cytology may also reveal other types of thyroid lesions, such as Hurthle cell adenomas or colloid nodules 4.
Comparison with Other Cytology Categories
- THY3a cytology has been reported to have a lower risk of malignancy compared to THY3f cytology, with some studies showing a malignancy rate of around 13-33% 3, 5.
- However, one study found that the malignancy rate for THY3a nodules was actually higher than for THY3f nodules, highlighting the need for careful evaluation and management of patients with indeterminate cytology results 5.
Rare Cases and Co-existence of Tumors
- In rare cases, a thy3f cytology may be associated with the co-existence of different types of thyroid carcinomas, such as papillary and medullary thyroid carcinoma 6.
- The clinical approach and treatment for such cases may need to be tailored to the specific types of tumors present and their dominance 6.