The definitive diagnosis and classification of individual cancers underpins the care of individual cancer patients, as well as research into the cause, prevention, diagnosis and treatment of cancer. Traditionally, cancer classification has been based on consensus of histopathological opinion, with very limited consideration of molecular pathology. But new technologies are transforming the field of pathology more rapidly than at any time in the last 30 years, and it is becoming increasingly clear that the traditional approach to cancer classification is insufficient. Our understanding of cancer at the molecular level has reached the point where this information should be included in diagnoses.
Digital pathology and image analysis are also producing new insights, providing quantitative justification for many existing diagnostic criteria and challenging others. Rapid improvement in computer technology, including artificial intelligence, is already producing clinically applicable diagnostic aids, and this trend is likely to accelerate. IARC has been responsible for the WHO Tumor Classification, also known as the WHO Blue Books, since the third edition (2000—200), which covered all organ sites in 10 volumes. Although the WHO1 document divides the molecular classification of the atlas7 PC genome into two large groups (BRAF type and Ras type), it also includes the main molecular characteristics of the different PC subtypes.
Although NIFTP shares the molecular alterations of thyroid tumors that show a follicular pattern and exhibits a high prevalence of mutations in the RAS gene family, it can sometimes be associated with fusions of the PPARG and THADA genes. A number of tumors remain whose cell lineage is unclear and are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. This review summarizes the changes in the fifth edition of the WHO Classification of Endocrine and Neuroendocrine Tumors related to the thyroid gland. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered a subtype of anaplastic carcinoma.
The current classification also emphasizes the value of biomarkers that can aid diagnosis and provide prognostic information. The IARC WHO Tumor Classification Group is responsible for the publication of the WHO Tumor Classification series, which is currently in its fifth edition. Although there is debate as to whether the cribiform-morular variant is a form of PC, it represents the form of thyroid cancer found in patients with familial adenomatous polyposis. Papillary thyroid carcinomas (PTC), with many morphological subtypes, represent BRAF-type malignancies, while invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent RAS-type malignancies.
Several unusual neoplasms that occur in the thyroid have been placed in new sections based on their cytogenesis. There is an urgent need to integrate these facets of diagnosis into the international classification of cancer and to update the WHO Tumor Classification on a regular basis. The association of adenolipomas with hamartoma tumor syndrome PTEN is emphasized, especially when they occur in young individuals with multiple thyroid nodules. This tumor variant is characterized by a high proliferation index (Ki-67 ≈ 10%), with frequent spread beyond the thyroid gland, relapses and metastases to and distant lymph nodes.