What is a common presentation of medullary carcinoma of the thyroid?

Medullary carcinoma of the thyroid is characterized by the malignant transformation of parafollicular C-cells, which are responsible for producing the hormone calcitonin. This type of thyroid cancer is unique as it arises from these neuroendocrine cells rather than the follicular cells that typically produce thyroid hormones (T3 and T4).

In medullary carcinoma, the overproduction of calcitonin can be a significant marker for the disease and is often assessed in patients presenting with thyroid nodules. The presence of increased levels of calcitonin in the blood can be a diagnostic clue, as elevated calcitonin levels are distinct to medullary thyroid carcinoma and help differentiate it from other types of thyroid cancer.

The role of calcitonin produced by C-cells involves regulation of calcium metabolism, lowering serum calcium levels by inhibiting osteoclast activity and renal tubular reabsorption of calcium. This highlights the importance of C-cells in calcium regulation and underscores why their tumorigenesis leads to the aforementioned pathological processes.

The other options presented relate to different aspects of thyroid function or conditions. Increased TSH levels typically indicate primary hypothyroidism and are not directly related to medullary carcinoma. Follicular cells produce T3 and T