Follicular thyroid carcinoma and NIFTP
- Lesion
Follicular cancer looks like normal thyroid tissue. It is called cancer only if it breaks through its capsule or into blood vessels.
What it is
Follicular carcinoma is composed of follicular cells without papillary nuclear features and is diagnosed only by invasion: through the full thickness of the capsule or into capsular vessels. It spreads through blood to bone, lung and liver rather than to lymph nodes. NIFTP is an encapsulated, non-invasive tumour with papillary-like nuclei that was reclassified from carcinoma because it almost never recurs; its invasive counterpart is the encapsulated follicular variant of papillary carcinoma.
Structure
- Gross: solitary, encapsulated or infiltrative; widely invasive tumours extend into the soft tissue of the neck.
- Micro: small follicles with little colloid, trabeculae or solid nests.
- Capsular invasion must pass through the full thickness; vascular invasion means tumour in a capsular or extracapsular vessel, covered by endothelium or with thrombus.
- Nuclei lack papillary features; psammoma bodies are absent.
Encapsulated follicular-patterned thyroid tumours
| Lesion | Nuclei | Invasion | Behaviour |
|---|---|---|---|
| Follicular adenoma | Bland | None | Benign |
| Follicular carcinoma | Bland | Capsular and/or vascular | Malignant, blood-borne spread |
| NIFTP | Papillary-like | None | Very low risk; not called carcinoma |
| Invasive encapsulated follicular variant of papillary carcinoma | Papillary-like | Capsular and/or vascular | Malignant, RAS-like |
| Oncocytic carcinoma | Oncocytic | Capsular and/or vascular | Malignant |
Clinical notes
- Presents as a cold nodule; sometimes the first sign is a bone metastasis.
- Well-differentiated metastases often take up radioiodine, which is used for imaging and therapy.
Test yourself
Think of the answer, then tap the question to see it.
What makes a follicular thyroid tumour a carcinoma?
Invasion through the full thickness of the capsule or into capsular or extracapsular vessels.
How does follicular carcinoma usually metastasise?
Through the bloodstream, to bone, lung and liver.
What is NIFTP?
Non-invasive follicular thyroid neoplasm with papillary-like nuclear features: an encapsulated, non-invasive tumour reclassified from carcinoma because of its very low risk.
Elsewhere in DurgiPedia
- Invasion and metastasis: the metastatic cascade, step by step
- Benign vs malignant tumours: the comparison table
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Thyroid Cancer Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2025); Thyroid Nodule (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.