Variants of Papillary Thyroid Cancer (PTC)

• Other variants of PTC:
  • Several variant subtypes of papillary thyroid cancer have been described:
    • Based upon histologic differences from classical papillary thyroid cancers:
      • But considered to be papillary cancers because of the characteristics of the tumor cell nuclei
• The insular variant of papillary thyroid cancer:
  • Histologically it is characterized by high cellularity with scant colloid and by well-definedsolid nests of tumor(insulae) of monotonous round cells:
    • Often separated by fibrous bands:
      • But the tumor cell nuclei have the same characteristics as do the nuclei of classical papillary thyroid cancers
  • Some tumors have papillary differentiation:
    • Whereas others are categorized as a variant of FTC
  • The mean tumor diameter at presentation is greater than 5 cm
  • Cervical nodal metastases:
    • Are seen in more than half of patients
  • Up to 70% have distant metastases
  • Viewed as an intermediate tumorbetween that of classic PTC and anaplastic thyroid carcinoma:
    • It is associated with 30-year cancer-specific mortality rate of 25% (versus 8% for classic PTC)
• The columnar variant, which consists of elongated cells with palisading nuclei:
  • This very rare subtype accounts for only 0.15% to 0.2% of all PTCs
  • It may be confused with TCV as its cells have a height twice the width:
    • But the elongated nuclei and prominent nuclear stratification distinguish it from other histologic variants
  • The encapsulated version of this tumor has a very good prognosis:
    • However, the diffusely invasive form is very aggressive
  • Unencapsulated tumors are:
    • Larger at presentation
    • Have a high rate of extracapsular spread
    • Have distant metastases:
      • In up to 87%
    • Mortality is significantly higher than it is for classic PTC
• The Hürthle or oxyphilic variant:
  • Which has cellular features of Hürthle cell carcinomas but cells that are arranged in papillary formations
• The solid or trabecular variant:
  • This tumor may be seen in adults:
    • But is more commonly associated with children after radiation exposure, particularly after the Chernobyl accident
  • Nuclear features:
    • Are similar to classic PTC
  • The architectural pattern:
    • Is predominantly or exclusively solid
  • The majority of tumors present with:
    • Extrathyroidal invasion
  • Cervical node metastases are common
  • In children, this tumor has a:
    • Similar survival rate as that of classic PTC
  • The prognosis is less clear for adults:
    • As conflicting mortality rates with this tumor have been described
• The clear cell variant:
  • Which must be distinguished from clear cell carcinomas of other organs such as:
    • The kidney or colon that have metastasized to the thyroid
• The diffuse sclerosing variant:
  • Characterized by:
    • Diffuse involvement of the thyroid
    • Stromal fibrosis
    • Prominent lymphocytic infiltration
  • This variant represents approximately:
    • 5% of all PTCs
  • Is seen more frequently in children:
    • Exposed to radiation at Chernobyl
  • A diffusely infiltrative tumor:
    • It is typically bilateral
    • With a high rate of lymph node metastases:
      • Approaching 70%
  • The histologic appearance of the tumor:
    • May be confused with chronic thyroiditis
  • It is characterized by:
    • Squamous metaplasia
    • Sclerosis
    • Psammoma bodies
    • Abundant lymphatic invasion
  • Rates of distant metastases are variably reported:
    • But appear to be higher than that of classic PTC
  • In spite of this seemingly aggressive behavior, there is debate about whether long-term prognosis is worse than for classic PTC
• The cribriform morular variant:
  • Which has a prominent cribriform pattern with solid and spindle cell areas as well as squamous morules
  • This variant is often associated with familial adenomatous polyposis
• The hobnail variant:
  • Harbors BRAF V600E mutations
  • Appears to be associated with a:
    • High risk of distant metastases and an increased disease-specific mortality
• These variants are all rare, and therefore, little information about their characteristics is available:
  • In general, however, they are thought to be more aggressive than classical papillary cancers
  • As a result, patients with these tumors are usually managed more aggressively than are those with classical papillary cancer of the same stage

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