GP section

thyroid

By far, most thyroid lumps are benign. However, thyroid lumps and thyroid cancer is increasing worldwide and NZ is no exception. We are iodine deficient but that is not the sole cause.

Around 85% cancers are papillary carcinoma, around 12% are follicular carcinoma, 5% medullary, and fortunately only 1-2% are anaplastic. Papillary and follicular are what we call "differentiated thyroid cancers"

About 6% of all patients with differentiated thyroid cancer will die of their disease....94% are either cured or live with dormant or active disease. As doctors we try to minimise the number dying by early diagnosis and treatment.

Differentiated (papillary and follicular)

Age at diagnosis is the single most important factor

Under 45yrs age

• The cure rate of a younger patient who is treated for a small intrathyroidal cancer is around 99%.
• It appears that having nodal disease has no impact on the prognosis! However these patients are at risk of nodal recurrences and may require repeated surgery which can increase morbidity (nerve palsy, hypocalcaemia).
• Even if there are systemic metastases the Cancer staging is only II (out of I -!V)! These young patients often live in a symbiotic relationship with their disease or perhaps eventually clear it through their own immune mechanisms.

Over the age of 45 yrs

• these patients usually also have a high cure rate.
• extension beyond the thyroid into surrounding neck tissues can occur.
• nodal disease appears to carry a worse prognosis longterm (higher risk of systemic metastases).
• higher rate of systemic metastases (yet these can often be kept under control or slowed by radioiodine).

Papillary (PTC)

• PTC is frequently present in an occult state (<1cm) and appears to have no clinical significance.
• 4% of thyroids that I remove for other reasons have occult PTC!
• clinically significant PTC is frequently multifical and is therefore treated with total thyroidectomy rather than just lobectomy. Usually also radioiodine.

Follicular (FTC)

• much less common
• pathologists have difficulty with the interpretation of these histologically
• are usually "minimally invasive" meaning the tumour is just extending through the capsule of the nodule into surrounding thyroid tissue.
• the most important feature is whether there is vascular invasion. A minimally invasive tumour without vascular invasion appears to have the same prognosis as a benign tumour.
• "Minimally invasive with vascular invasion" is treated with total thyroidectomy and radioiodine because of risk of metastases.
• "Widely invasive follicular carcinomas" have vascular invasion and have a poorer prognosis. Treated with total thyroidectomy and radioiodine.

Medullary carcinoma (MTC)

• intermediate grade cancers.
• most are sporadic and unilateral.
• high rate of nodal involvement.
• some are familial and may be part of MEN 2 syndrome.
• treated with total thyroidectomy and neck node clearance (neck dissections). No radioiodine as from C-cells and not thyroid follicular cells.

Anaplastic

• aggressive malignancies that have average life expectancy of 6 months.
• arise from a sequence of genetic hits on a thyroid cell. There is an evolution from low grade malignancy to higher grade to undifferentiated to anaplasia.
• present as rapidly growing hard thyroid mass with airway compression.
• urgent referral to surgeon for diagnosis and airway management.
• critical to differentiate from lymphoma which can present in same way and is very treatable with radiotherapy