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Long-term follow-up of patients with differentiated thyroid carcinomas
was 2 decades ago based on whole body scans (wbs) with I-131, supplemented
with X-rays, bone scintigraphy and in some cases CT-scans and ultrasound
of the neck. Many of these procedures have to some extent been replaced
by the use of the tumour marker thyroglobulin (Tg), which is produced only
by thyroid follicular cells. In an athyrotic individual (e.g. after total
thyroidectomy) a measurable value for Tg in serum can theoretically only
be derived from metastatic or relapsing thyroid carcinoma cells. The methods
for measurement of serum Tg have, however, turned out to be liable to false
results in the presence of TgAb(l7 18,19, 20). The proportion of thyroid
carcinoma patients with TgAb has been reported very variably from 5 to
20 % depending on the selection of the patients and the TgAb method used
for measurement. The presence of TgAb does not seem to influence the prognosis
of the disease(2lS 22), only disturbs the utility of serum Tg as a tumour
marker.
It is possible that patients with obvious metastatic disease and no TgAb are negative for serum Tg. On the other hand, about 13% of patients with a negative I-131 uptake on wbs and evidence of metastases by either lung X-ray or bone scintigrahy turned out to have measurable and often elevated serum Tg levels(23). Much emphasis has thus been put on serum Tg as a tumour marker since it was also demonstrated that patients with elevated serum Tg levels and subsequently treated with I-131 normalized their serum Tg (23). From previous and recent methodological studies of serum Tg measurements it, however, appears that:
With these caveats in mind a suggested workup of post-therapy differentiated thyroid carcinoma is presented in Fig 1. Since differentiated thyroid carcinoma is a potentially curable disease yet with a life-long need for follow-up due to late recurrence/metastases it is a disease to be often controlled in less experienced hands. The introduction of serum Tg as a tumour marker has further fascilitated the control to be performed in less experienced services. It, however, still has to be emphasized that differentiated thyroid carcinoma is a potentially curable disease, and the recurrence/metastases are also potentially curable provided they are revealed at an early stage. Due to the present difficulties of judging both the results of the serum Tg measurements as well as the other evidences of recurrence (e.g. I-131 wbs) the follow-up is at best left with specialists in this particular field, in order to treat present patients the best way possible and also in order to obtain the best possible evidence for future treatment and follow-up procedures. For patients with medullary thyroid carcinomas the follow-up procedure is focusing on the elevation of basal or pentagastrin stimulated serum calcitonin levels. However, future early thyroidectomies of RET oncogene mutation positive individuals of MEN 2A families should eventually diminish this problem(7). The non-familial forms are still subject to the previous follow-up schedules monitoring serum calcitonin. Figure 1: Work-up of differentiated thyroid carcinoma
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