Follicular thyroid cancer diagnostic study of choice

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]

Overview

Biopsy is the gold standard for diagnosing thyroid cancer. According to the American Joint Committee on Cancer (AJCC), there are 4 stages of follicular thyroid cancer based on the clinical features and findings on imaging. Each stage is assigned a letter and a number that designate the tumor size, number of lymph node regions involved, and metastasis.

Diagnostic Study of Choice

Study of Choice

• Biopsy is the gold standard for diagnosing thyroid cancer.
• Biopsy can be taken by the following methods:

1. Fine Needle Aspiration Biopsy (FNAC)

• The removal of thyroid tissue using a thin needle. The needle is inserted through the skin into the thyroid. Several tissue samples are removed from different parts of the thyroid.

2. Surgical Biopsy

• Surgical biopsy is the removal of the thyroid nodule or one lobe of the thyroid during surgery.
• On microscopic examination, trabecular follicular tumor cells that invade tumor capsule or surrounding vascular structures are found.

Staging

Thyroid TNM staging

Stage	Description
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Tumor ≤ 2 cm in greatest dimension limited to the thyroid
T1a	Tumor ≤ 1 cm, limited to the thyroid
T1b	Tumor > 1 cm but ≤ 2 cm in greatest dimension, limited to the thyroid
T2	Tumor > 2 cm but ≤ 4 cm in greatest dimension, limited to the thyroid
T3	Tumor > 4 cm in greatest dimension limited to the thyroid or any tumor with minimal extrathyroid extension (e.g., extension to sternothyroid muscle or perithyroid soft tissues)
T4a	Moderately advanced disease
	Tumor of any size extending beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4b	Very advanced disease
	Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessel

Regional Lymph Nodes (N)

Stage	Description
NX	Regional lymph node cannot be assessed
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
N1a	Metastases to Level VI (pretracheal, paratracheal, and prelaryngeal/Delphian lymph nodes)
N1b	Metastases to unilateral, bilateral, or contralateral cervical (Levels I, II, III, IV, or V) or retropharyngeal or superior mediastinal lymph nodes (Level VII)

Distant Metastasis (M)

Stage	Description
M0	No distant metastasis
M1	Distant metastasis

Anatomic Stage/Prognostic Groups

Stage	T	N	M
Follicular thyroid carcinoma
YOUNGER THAN 45 YEARS
I	Any T	Any N	M0
II	Any T	Any N	M1
45 YEARS AND OLDER
I	T1	Any N	M1
II	T2	N0	M0
III	T3	N0	M0
	T1	N1a	M0
	T2	N1a	M0
	T3	N1a	M0
IVA	T4a	N0	M0
	T4a	N1a	M0
	T1	N1b	M0
	T2	N1b	M0
	T3	N1b	M0
	T4a	N1b	M0
IVB	T4b	Any N	M0
Stage IVC	Any T	Any N	M1

Follicular Thyroid Cancer

Stage I Follicular Thyroid Cancer

• Stage I follicular carcinoma is localized to the thyroid gland. Follicular thyroid carcinoma must be distinguished from follicular adenomas, which are characterized by their lack of invasion through the capsule into the surrounding thyroid tissue.

Stage II Follicular Thyroid Cancer

• Stage II follicular carcinoma is defined as either tumor that has spread distantly in patients younger than 45 years, or tumor that is larger than 2 cm but smaller than 4 cm and is limited to the thyroid gland in patients older than 45 years. The presence of lymph node metastases does not worsen the prognosis among patients younger than 45 years. Follicular thyroid carcinoma must be distinguished from follicular adenomas, which are characterized by their lack of invasion through the capsule into the surrounding thyroid tissue. While follicular cancer has a good prognosis, it is less favorable than that of papillary carcinoma. The 10-year survival is better for patients with follicular carcinoma without vascular invasion than for patients with vascular invasion.

Stage III Follicular Thyroid Cancer

• Stage III follicular carcinoma in patients older than 45 years is defined as tumor larger than 4 cm and limited to the thyroid or with minimal extrathyroid extension, or lymph node involvement limited to the pretracheal, paratracheal, or prelaryngeal/Delphian nodes.

Stage IV Follicular Thyroid Cancer

• Stage IV follicular carcinoma in patients older than 45 years is defined as tumors with extension beyond the thyroid capsule to the soft tissues of the neck, cervical lymph node metastases, or distant metastases. The lungs and bone are the most frequent sites of spread. Follicular carcinomas more commonly have blood vessel invasion and tend to metastasize hematogenously to the lungs and to the bone rather than through the lymphatic system.