Thyroid cancer
Pathology
Approximate Frequency of Malignant Thyroid Tumors.
Papillary carcinoma (including mixed papillary and follicular) 80
%
Follicular carcinoma (including Hürthle cell carcinoma) 10
%
Medullary carcinoma 5
%
Undifferentiated carcinomas 3
%
Miscellaneous (including lymphoma, fibrosarcoma, squamous cell carcinoma, malignant hemangioendothelioma, 1
teratomas, and metastatic carcinomas) %
Papillary Carcinoma
• Papillary carcinoma of the thyroid gland usually presents
as a nodule that is firm, solitary, "cold" on isotope scan,
solid on thyroid ultrasound, and clearly different from
the rest of the gland.
• In multinodular goiter, the cancer is usually a "dominant
nodule"—larger, firmer, and (again) clearly different
from the rest of the gland.
• About 10% of papillary carcinomas, especially in
children, present with enlarged cervical nodes, but
careful examination often reveals a nodule in the
thyroid.
Papillary Carcinoma
• Microscopically, the tumor consists of single layers
of thyroid cells arranged in vascular stalks, with
papillary projections extending into microscopic
cyst-like spaces. The nuclei of the cells are large
and pale and frequently contain clear, glassy
intranuclear inclusion bodies. About 40% of
papillary carcinomas form laminated calcified
spheres—often at the tip of a papillary projection
—called "psammoma bodies," which are usually
diagnostic of papillary carcinoma.
Papillary Carcinoma
• These cancers usually extend by intraglandular
metastasis and by local lymph node invasion.
• They grow very slowly and remain confined to
the thyroid gland and local lymph nodes for
many years. In older patients, they may
become more aggressive and invade locally
into muscles and trachea.
Papillary Carcinoma
• In later stages, they can spread to the lung. Death is usually due to
local disease, with invasion of deep tissues in the neck; less commonly,
death may be due to extensive pulmonary metastases.
• In some older patients, a long-standing, slowly growing papillary
carcinoma begins to grow rapidly and converts to undifferentiated or
anaplastic carcinoma. This "late anaplastic shift" is another cause of
death from papillary carcinoma.
• Many papillary carcinomas secrete thyroglobulin, which can be used as
a marker for recurrence or metastasis of the cancer.
• Most papillary cancers concentrate radioiodine, albeit much less
efficiently than normal thyroid tissue: this is why they appear as "cold"
nodules on radionuclide scan. But, for this same reason, radioiodine
can be used as the primary therapy for recurrent or metastatic disease.
Follicular Carcinoma
• Follicular carcinoma is characterized histologically
by the presence of small follicles, although colloid
formation is poor
• The tumor is somewhat more aggressive than
papillary carcinoma and can spread either by local
invasion of lymph nodes or by blood vessel invasion
with distant metastases to bone or lung.
• Microscopically, the cells are cuboidal, with large
nuclei, arranged around follicles that frequently
contain dense colloid.
Follicular Carcinoma
• These tumors often retain the ability to
concentrate radioactive iodine, to form
thyroglobulin, and, rarely, to synthesize T3 and T4.
Thus, the rare "functioning thyroid cancer" is
almost always a follicular carcinoma. This
characteristic makes these tumors more likely to
respond to radioactive iodine therapy. Death is
due to local extension or to distant bloodstream
metastasis with extensive involvement of bone,
lungs, and viscera.
Medullary Carcinoma
• Medullary cancer is a disease of the C cells
(parafollicular cells) derived from the
ultimobranchial body and capable of secreting
calcitonin, carcinoembryonic antigen (CEA),
histaminase, prostaglandins, serotonin, and
other peptides.
Medullary Carcinoma
• Medullary carcinoma is somewhat more aggressive
than papillary or follicular carcinoma but not as
aggressive as undifferentiated thyroid cancer.
• It extends locally into lymph nodes and into
surrounding muscle and trachea. It may invade
lymphatics and blood vessels and metastasize to
lungs and viscera.
• Calcitonin and CEA secreted by the tumor are
clinically useful markers for diagnosis and follow-
up.
Undifferentiated (Anaplastic) Carcinoma
• Undifferentiated thyroid gland tumors include
small cell, giant cell, and spindle cell carcinomas.
They usually occur in older patients with a long
history of goiter in whom the gland suddenly—
over weeks or months—begins to enlarge and
produce pressure symptoms, dysphagia, or vocal
cord paralysis. Death from massive local
extension usually occurs within 6–36 months.
These tumors are very resistant to therapy.
