Thyroid Cancer - Diagnosis - Classification

Classification

Thyroid cancers can be classified according to their histopathological characteristics. The following variants can be distinguished (distribution over various subtypes may show regional variation):

• Papillary thyroid cancer (75% to 85% of cases ) – often in young females – excellent prognosis. May occur in women with familial adenomatous polyposis and in patients with Cowden syndrome.
• Follicular thyroid cancer (10% to 20% of cases ); occasionally seen in patients with Cowden syndrome
• Medullary thyroid cancer (5% to 8% of cases)- cancer of the parafollicular cells, often part of multiple endocrine neoplasia type 2.
• Poorly differentiated thyroid cancer
• Anaplastic thyroid cancer (Less than 5%). It is not responsive to treatment and can cause pressure symptoms.
• Others
  • Thyroid lymphoma
  • Squamous cell thyroid carcinoma
  • Sarcoma of thyroid

The follicular and papillary types together can be classified as "differentiated thyroid cancer". These types have a more favorable prognosis than the medullary and undifferentiated types.

• Papillary microcarcinoma is a subset of papillary thyroid cancer defined as measuring less than or equal to 1 cm. The highest incidence of papillary thyroid microcarcinoma in autopsy series was reported by Harach et al. in 1985, who found 36 of 101 consecutive autopsies were found to have an incidental microcarcinoma. Michael Pakdaman et al. report the highest incidence in a retrospective surgical series at 49.9% of 860 cases. Management strategies for incidental papillary microcarcinoma on ultrasound (and confirmed on FNAB) range from total thyroidectomy with radioactive iodine ablation to observation alone. Harach et al. suggest using the term "occult papillary tumor" to avoid giving patients distress over having cancer. It was Woolner et al. who first arbitrarily coined the term "occult papillary carcinoma" in 1960, to describe papillary carcinomas ≤ 1.5 cm in diameter.