The treatment of differentiated thyroid cancer (DCT) includes surgery followed by radioiodine treatment. In the follow-up of patients it is necessary to induce TSH elevation to test for cancer recurrence. One of the options is to stop L-thyroxin replacement for several weeks. Current pilot study aims to induce the necessary TSH elevation by decreasing the L-thyroxin dose. The main hypothesis is that necessary TSH stimulation will be achieved during 4-6 weeks in majority of patients.

The treatment of differentiated thyroid cancer (DCT) includes surgery followed by radioiodine treatment. In the follow-up of patients it is necessary to induce TSH elevation for the measurement of thyreoglobulin and/or total body scanning. There are two principal methods to obtain TSH elevation: 1) injection of recombinant human TSH , and 2) to stop L-thyroxin replacement for several (3-4) weeks. As use of recombinant TSH is rather expensive, this method is not feasible in many countries. The problem with stopping L-thyroxin is development of severe hypothyroidism for several weeks with concomitant symptoms and signs.

Current pilot study aims to induce the necessary TSH elevation by decreasing the L-thyroxin dose. The main hypothesis is that necessary TSH stimulation will be achieved during 4-6 weeks in majority of patients with fixed dose of L-thyroxin. Concomitantly, blood tests and symptoms and signs of hypothyroidism will be obtained to get information about possible deviations during treatment with low dose of thyroxin.

Inclusion Criteria:

• Differentiated thyroid cancer
• treated by thyroidectomy and at least 1 ablation with 131-I > 5 months ago
• TSH < 4 imU/L

Exclusion Criteria:

• Pregnancy
• Known metastasis