A 44-year-old man sees his physician because he felt a “lump” on the left side of his neck. Physical examination shows
a nontender nodule on the left lobe of the thyroid gland. A cervical node is enlarged and nontender. Laboratory studies
show no thyroid autoantibodies in his serum, and the T4 and TSH levels are normal. A thyroidectomy is performed; the
figure shows the high-power microscopic appearance of the nodule. Which of the following is most likely to contribute to
the development of the thyroid nodule in this patient?
A. Chronic dietary iodine deficiency B. Tyrosine kinase receptor gene mutation C. Consumption of goitrogens D. Adrenal medullary pheochromocytoma E. Viral infection
Tyrosine kinase receptor gene mutation-(b) the nodule shows a papillary architecture, with cells that have clear nuclei; this pattern is typical of a papillary
carcinoma. there is no such thing as a papillary adenoma. the enlarged clear nuclei are typical of papillary carcinoma.
these nuclear changes, even if the pattern is follicular, confirm the diagnosis of papillary carcinoma. about 30% of all
papillary thyroid carcinomas have mutational activation of ret or ntrk1 proto-oncogenes, which belong to the family of
receptor tyrosine kinases that transduce extracellular signals for cell growth and differentiation and exert many of their
downstream effects through the ubiquitous map kinase signaling pathway. iodine deficiency gives rise to uniform thyroid
enlargement because the secretion of tsh increases when there is reduced synthesis of t4. goitrogens interfere with
thyroid hormone synthesis and have an effect similar to that of iodine deficiency. an adrenal pheochromocytoma can occur
with medullary carcinoma of the thyroid in multiple endocrine neoplasia (men) type iia or men type iib. viral infections can
cause a subacute thyroiditis, not carcinoma.
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