Thallium-201, technetium-99m-tetrofosmin and iodine-131 in detecting differentiated thyroid carcinoma metastases

The purpose of this study was to asses the detectability of differentiated thyroid carcinoma (DTC) metastases by 99mTc-tetrofosmin and to compare the results of 99mTc-tetrofosmin with 131I and 201Tl. The reliability of 201Tl and 99mTc-tetrofosmin scanning during suppression therapy also has been studied. METHODS: A prospective study was performed on 41 patients (30 females, 11 males) with DTC (30 papillary, 11 follicular) who had undergone total thyroidectomy and received an average dose of 117 mCi (4329 MBq) of radioiodine for ablation of postsurgical residual thyroid tissue. All patients (n = 41) had 201Tl, 99mTc-tetrofosmin or 131I whole-body imaging after discontinuation of thyroid hormone replacement (thyroxine-off group). Eight of 14 patients with distant metastases also were imaged when they were on thyroxine therapy both with 201Tl and 99mTc-tetrofosmin (thyroxine on-and-off group). Radiologic studies (chest radiography, CT and MRI), serum thyroglobulin assays and histopathologic examinations were performed to clarify the presence of metastases with positive uptake on any of three radionuclide studies. RESULTS: In 26 of 41 patients all three scans were negative. These patients also clinically didn't show any evidence of metastases. Fourteen patients were considered to have distant metastases on the basis of clinical, radiologic and histopathologic findings. The sensitivities of 201Tl, 99mTc-tetrofosmin and 131I in diagnosing distant metastases were comparable (0.85, 0.85 and 0.78, respectively). Iodine-131 was much more sensitive than 201Tl and 99mTc-tetrofosmin for demonstrating residual thyroid tissue after surgery (1.00, 0.33 and 0.33, respectively). The only false-positive case involved radioiodine uptake in a tuberculoma. Thyroxine-on images of 8 patients with distant metastases showed no difference from their thyroxine-off images regarding the site, number and uptake of metastases. CONCLUSION: Technetium-99m-tetrofosmin and 201Tl imaging are highly sensitive for detecting differentiated thyroid carcinoma metastases and do not require prior withdrawal of thyroid hormone suppressive therapy.     

The in vitro effect of ridogrel on platelet function in normocholesterolaemic and familial hypercholesterolaemic type IIa subjects

Iodine-131 whole body imaging and serum thyroglobulin are used in the follow-up evaluation of differentiated thyroid carcinomas. Iodine 131 is used to detect and treat functioning lesions. Iodine 131 activity detected outside the normal thyroid bed is usually attributed to metastatic disease. False-positive localization of radioiodine has been described, and may be a potential pitfall. We report here six personal cases of false-positive localisations of radioiodine du to body secretions, pathologic exudate, activity in nonlactating breast, salivary gland inflammation, ovarian teratoma. Some of these false-positive can be ruled out easily by removing of clothes, removing of nozzle in patients with tracheostomy, or by ingestion of water in subjects with abnormal mediastinal hyperfixation. Recognition of false-positive radioiodine images is very important to prevent costly additional investigation and possibly inappropriate therapy.     

Changes of angiogenin serum concentrations in the perinatal period

We report a 49-year-old woman with Marfan syndrome who underwent total thyroidectomy for follicular carcinoma. The patient was given 100 mCi of radioactive iodine (131I) followed by levothyroxine (LT4) 0.2 mg/day after surgery. The subsequent five total body scans were negative and thyroglobulin (TG) measurements ranged between undetectable levels to 12 ng/mL. Nine years after thyroidectomy the patient developed bilateral exophthalmos with markedly positive thyroid-stimulating immunoglobulins (TSI), indicating the presence of Graves' disease. TG levels increased and concurrently pulmonary metastases that did not concentrate radioiodine at tracer doses, were diagnosed. Due to these metastatic lesions, the patient received a therapeutic dose of 150 mCi of 131I 1 month after LT4 withdrawal, and a total body scan was made 10 days later. Slight uptake of 131I was found in the right side of the neck, whereas predominant uptake occurred in the right lung base. We suggest that the elevated TSI played a role in the growth of metastases.     

Radioiodine ablation of residual tissue in thyroid cancer: relationship between administered activity, neck uptake and outcome

A retrospective review was performed to evaluate the effectiveness of radioiodine in the ablation of residual thyroid tissue after surgery for differentiated thyroid cancer. 121 patients were treated at the Princess Margaret Hospital, Toronto, Canada between 1977 and 1989, with the activity of radioiodine determined empirically. Ablation of residual thyroid was determined by 131I nuclear scans, using absent visible uptake (compared with background) as the criterion for successful ablation. 97 patients (80%) had successful ablation of residual thyroid tissue after the first administration of radioiodine. Patients with higher iodine uptake in the neck had a tendency to receive higher activities of 131I. There were no statistically significant differences in age, sex, type of surgery, initial iodine uptake in the neck and administered radioiodine activity between those successfully ablated and those that were not. Patients receiving less than 3.7 GBq (100 mCi) tended to have lower iodine uptake (< 5% at 24 or 48 h), but their rate of thyroid ablation was just as high as those given 3.7 GBq or more. In order to take advantage of this, we have formalized our approach by deriving guidelines to the empiric determination of radioiodine activity based on the iodine uptake in the neck. Among the 11 patients treated with lobectomy only, the ablation rate was 64%. Although this was not significantly lower than for other forms of surgery, we continue to recommend completion thyroidectomy for this group of patients, if the goal of treatment is to ablate all thyroid tissue.     

Advanced trauma life support versus Combat Trauma Life Support courses: a comparison of cognitive knowledge decline

Post-thyroidectomy I-131 whole-body scintigraphy is an important aspect in the management of patients with thyroid cancer. The scan is used to detect residual thyroid tissue and distant functioning metastases. Extrathyroid I-131 accumulation does not always denote metastatic disease, and several potential sources of false-positive I-131 scans have been identified. This report presents four cases of benign oral disease as a cause of false-positive I-131 uptake. Benign oral disease has not been documented previously as an important source of false-positive I-131 whole-body scans.     

131I treatment of 131I negative whole body scan, and positive thyroglobulin in differentiated thyroid carcinoma: what is being treated?

Several aspects of the management of differentiated thyroid cancer cause considerable controversy. Among these is the role of 131I therapy in patients after thyroidectomy. There is no controlled study to demonstrate whether this treatment reduces the recurrence rate or improves mortality. Because of the overall excellent prognosis, it is unlikely that a controlled study will ever be conducted. Most frequently, patients have a diagnostic scan with 131I to determine whether radioiodine would be an appropriate therapy and to judge much to be prescribed, based on the extent of abnormalities seen on the scintiscan. Serum thyroglobulin (Tg) has been found to be a valuable tumor marker, with very good sensitivity and specificity. In most patients, the result of whole-body 131I scintiscan and Tg measurement give concordant results. However, in some patients, Tg is measurable, but the diagnostic scan with 131 is normal. There has been data published about treatment of these patients with therapeutic doses of 131I. The author questions whether this treatment is appropriate, prompted by seeing and hearing of patients who were treated with therapeutic doses of 131I, but had no abnormal uptake of the therapeutic doses and who had no improvement in serum Tg level. These patients have no clinical evidence of disease, and the only abnormality is measurable Tg. Since large doses of radioiodine are not without problems, a controlled clinical trial should be developed to evaluate efficacy in this situation.     

Breast cyst simulating metastases on iodine-131 imaging in thyroid carcinoma

False-positive radioiodine uptake has been reported in many organ systems. We describe a female patient who had mixed papillary and follicular thyroid carcinoma, and on radioiodine total-body imaging demonstrated focal, lower-right chest uptake. Special prone imaging with the right breast dependent proved that the uptake was inside the right breast. Review of a recent breast ultrasound and mammograms showed this uptake to correspond to a large breast cyst. It is known that 131I breast uptake may be functional within the mammary gland. In this patient, it was due to retention within the cyst after the background activity decreased. Knowledge of this phenomenon may improve the interpretation of total-body 131INa studies.     

The role of iodine-131 and thallium-201 imaging and serum thyroglobulin in the management of differentiated thyroid carcinoma

BACKGROUND: A prospective study was conducted to evaluate the use of iodine-131 sodium scintigraphy, thallium-201 chloride scintigraphy, and quantitative serum thyroglobulin estimation in the detection of differentiated thyroid carcinoma after thyroidectomy and iodine-131 sodium ablative therapy. METHODS: Thirty-one patients with a median age of 45.6 years (range, 20-73 years) were included in the study. After optimal endogenous thyroid-stimulating hormone stimulation (> 50 mU/ml), 53 pairs of iodine-131 and thallium-201 scans were performed. Concomitant serum thyroglobulin levels were available for 32 pairs of scans. The presence or absence of thyroid cancer was established by clinical, radiologic, and/or biopsy findings. RESULTS: The concordance between iodine-131 and thallium-201 scan findings in the presence of disease (25 scan sets) was 36%. The concordance in the absence of disease (28 scan sets) was 82%. Iodine-131 scanning was found to be significantly better (P < 0.05) than thallium-201 scanning, in terms of sensitivity (0.8 versus 0.6), specificity (0.96 versus 0.82), accuracy (0.89 versus 0.72), and the predictive value of a positive test (0.95 versus 0.75). The measurement of serum thyroglobulin had a low sensitivity (0.3) in the study but had a specificity of 1.0. CONCLUSION: It was concluded that iodine-131 sodium scintigraphy is superior to thallium-201 scintigraphy and serum thyroglobulin estimation for the detection of residual or metastatic differentiated thyroid carcinoma. However, the use of combined modalities provides a higher diagnostic yield. Thallium-201 scintigraphy was especially useful in cases in which iodine-131 scintigraphy was negative and quantitative thyroglobulin levels were elevated.     

Thallium-201 scintigraphy to predict therapeutic outcome of iodine-131 therapy of metastatic thyroid carcinoma

We studied the relationship between 201Tl uptake and the efficacy of radioiodine therapy in thyroid carcinoma. METHODS: Forty-four patients with metastases of well-differentiated thyroid carcinoma received 201Tl scintigraphy within the 2 mo before their initial 131I therapy. Patients were classified into two groups according to the tumor-to-background (T/B) ratio on the late 201Tl scan: high 201Tl uptake (T/B > or = 2.1) and low 201Tl uptake (T/B < 2.1). The therapeutic outcome was judged by the percent reduction in the tumor diameter at 6 mo after the treatment. The treatment was defined as effective when the tumor showed more than 50% reduction in the tumor diameter. The patients in whom radioiodine was ineffective were followed up to determine if the tumor showed further growth. RESULTS: Of the 44 patients, 25 had high 201Tl uptake and 19 had low 201Tl uptake. The therapy was effective in 15 patients and was ineffective in 29. All the patients in whom radioiodine was effective had low 201Tl uptake. On the other hand, 25 of 29 patients in whom radioiodine was ineffective had high 201Tl uptake. Eight patients, in whom radioiodine was ineffective despite good 131I uptake, had high 201Tl uptake. There were no significant differences in the positive predictive value and the negative predictive value for effective treatment between 201Tl scintigraphy and therapeutic dose 131I scintigraphy. Among the 25 patients in whom radioiodine was ineffective and who had high 201Tl uptake, the tumor diameter increased in 7 (28%). However, none of the tumors with low 201Tl uptake increased in size during the follow-up period. CONCLUSION: Thallium-201 scintigraphy has a high predictive value for the efficacy of radioiodine therapy in metastatic thyroid carcinoma. Thus, it is helpful in determining the indication for radioiodine therapy and it seems to be an adjunct to tracer dose 131I scintigraphy.     

Improvement of the merthiolate-iodine-formalin (MIF) fecal technique for hookworm, Trichuris trichiura, and Ascaris lumbricoides eggs

A patient with a history of total thyroidectomy for papillary carcinoma showed a solitary hot spot in the chest on post-therapy radioiodine imaging. Subsequent evaluation demonstrated that this lesion was a primary squamous-cell lung cancer. Our case illustrates a rare but important differential diagnosis from lung metastasis of thyroid cancer in 131I scintigraphy. Alternatively, this "aberrant uptake" might be a rather common phenomenon for lung neoplasms, although the underlying mechanism is not yet known. Future experimental studies might lead to a new application of radioiodine imaging in pulmonary oncology.     

Urinary bladder organ culture with a continuous nutrient system]

From the differences in radiation profiles between 131I and 125I isotopes of iodine it would be expected that they would show different effects on thyroid function. The differences should lead to lower rates of thyroid gland destruction with 125I and hence less post-irradiation hypothyroidism. This difference in biological effect has been demonstrated in rats by indirect assessment of thyroid function. In this report the long-term effects of a range of similar doses of 131I and 125I were compared, in male and female rats, by direct assessment of thyroid function. Seventeen months after receiving 25 and 125 muCi of 131I, male and female rats showed significant elevation of serum TSH concentration and a reduction in 3 h radioiodine uptake. Rats receiving 1 and 5 muCi of 131I and all doses of 125I showed no significant changes in thyroid function. These findings confirm the previously reported differences in effect between the 131I and 125I isotopes of iodine in the rat.     

The correlation of the vasopressin- and oxytocin-producing activities of different nuclei in the hypothalamo-hypophyseal neurosecretory system]

Radioiodine long has proven to be a safe and effective treatment for thyroid disease. Nonetheless, persisting concerns regarding radiogenic stochastic risks (e.g., carcinogenesis) to patients, their families, and the general public have led regulators to establish criteria for release of 131I-containing patients from medical confinement, with limits ranging from as low as 2 mCi in some parts of Europe to as high as 30 mCi in the United States. To optimize clinical efficacy and cost-effectiveness of 131I therapy, such regulations should be based on logical dosimetric considerations. The thyroidal absorbed dose, proportional to maximum uptake and effective half-life and inversely proportional to mass, is typically approximately 1,500 rad/mCi of 131I administered to a euthyroid adult (based on a thyroid maximum uptake of 25%, effective half-life equivalent to the physical half-life of 131I (8.04 days), and mass of 20 g). As thyroid uptake increases from 0% to 100%, extrathyroidal absorbed doses range from a minimum of 0.15 to 0.5 rad/mCi for breast and gonads to a maximum of 1.5 to 2 rad/mCi for stomach and salivary glands; the absorbed doses of the urinary bladder wall, in contrast, decrease with increasing thyroid uptake, from 2 to 0.6 rad/mCi. In hyperthyroid patients (approximately 15%) with a small iodine pool (so-called small patients), the short effective half-life of radioiodine in the thyroid and high serum concentrations of long-lived protein-bound 131I result in a standard 7,000-rad absorbed dose for treatment of Graves' disease requiring an administered activity of 28 mCi of 131I and yielding a prohibitively high blood absorbed dose of 150 rad. Importantly, once the fetal thyroid begins to function and accumulate radioiodine at a gestational age of 10-12 weeks, fetal thyroid absorbed doses as large as 5,000 rad/mCi of 131I administered to the mother can result. Thus, pregnancy is an absolute contraindication to administration of 131I because of the risk of radiogenic cretinism. Based on actual measurements of thyroid activity and of external absorbed dose, the total thyroid and mean extrathyroidal absorbed doses to adult family members from immediately released 131I-treated patients are approximately 0.01 and approximately 0.02 rad/mCi administered, respectively, yielding an effective dose of approximately 0.02 rem/mCi. A maximum permissible effective dose of 0.5 rem for adults therefore is consistent with a release criterion of 30 mCi of retained 131I. Lower-activity release criteria therefore may be unnecessarily restrictive.     

I-131 uptake in the breast for thyroid cancer surveillance with biopsy-proven benign tissue

A 37-year-old woman was seen for recurrent papillary carcinoma of the thyroid after thyroidectomy. After repeated surgery and I-131 therapy, follow-up I-131 scanning and thyroglobulin levels were negative. Subsequent I-131 surveillance, however, demonstrated bilateral breast uptake. A biopsy taken of this area in the right breast proved that the increased uptake was secondary to benign disease.     

Variations of the flexor digitorum superficialis tendon of the little finger

The use of 131I doses of several mCi for scans can stun the thyrocytes and thyroid cancer cells, whereas the usual dose (300 microCi) of 123I does not. We compared the diagnostic accuracy of the 123I (300 microCi) scans and that of 131I (3-10 mCi) scans in 155 patients. The diagnostic accuracy of a 123I scan in detecting functioning thyroid remnant/metastasis was 89.5% (77/86 scans) and that of a 131I scan was 92.9% (39/42) in 6 week-postoperative patients (p = 0.750). For radioablation therapy follow-up patients, the diagnostic accuracy of 123I in determining presence or absence of functioning remnant or metastasis was 69.4% (25/36) and that of 131I was 92.5% (49/53) with a p value of 0.079. The success rates for complete ablation of functioning tissue after radioiodine therapy administered after diagnostic 123I and after 131I were 72% (34/47) and 56% (24/43), respectively, with a p value of 0.125. Our study indicates the following: 1) for the first postoperative evaluation, the diagnostic accuracy of the 123I scan was essentially equal to that of the 131I scan, and the success rate of radioablation therapy appears to be better than 123I scan; and 2) for postablation follow-up surveys, the 131I scan appears to be better but carries the risk of stunning the functioning cells.     

Pulmonary metastases in children and adolescents with well-differentiated thyroid cancer

In this study, 27 patients less than 18 yr old with pulmonary metastases from well-differentiated thyroid carcinoma were evaluated to determine their response to (131)I therapy. METHODS: Of 121 children and adolescents treated with (131)I between 1963 and 1996, 27 patients had pulmonary metastases associated with nodal disease. Treatment response from (131)I was measured by three parameters: chest radiograph, scintigraphic images and serum thyroglobulin levels. Total activity of (131)I administered ranged from 4.6 GBq (125 mCi) to 38.7 GBq (1.05 Ci). Four patients were given one treatment, 8 were given two treatments, 4 were given three treatments and 11 were given more than three treatments. Radiation doses to the lungs were estimated in 14 patients using the MIRD methodology. The minimum duration of follow-up was 6 mo. RESULTS: At the time of initial presentation, diagnostic (131)I studies revealed bilateral radioiodine uptake in the lungs in 19 (70.4%) patients, whereas 12 (44.4%) patients had abnormal chest radiographs. One patient was lost to follow-up and was excluded from the study. Of the 26 patients studied, complete ablation of pulmonary metastases was observed in 8 (30.8%), partial ablation in 17 (65.4%) and there was no response to treatment in 1 (3.8%). Dosimetric parameters such as radioiodine uptake as a percentage of therapeutic activity, effective half-life and radiation dose delivered to the lungs were evaluated with each therapy. There was a progressive decline in each of these parameters with successive therapies. No correlation was observed between the radiation dose delivered and the response of pulmonary metastases to therapy. The number of therapies and amount of radioiodine administered had no influence on the ablation response. Of the 26 patients, 13 had a follow-up duration of less than 5 yr, 7 had 5-10 yr and 6 had more than 10 yr. One patient developed new metastases after 7 yr of diagnosis and treatment. One patient died of the disease after 4 yr. All surviving patients were asymptomatic and leading normal lives. CONCLUSION: Complete response of pulmonary metastases after (131)I therapy is difficult to achieve. A partial response with reduction of metastatic disease is possible and, in general, the patients had a good quality of life with no further disease progression and a low mortality rate.     

Outcome of 309 patients with metastatic differentiated thyroid carcinoma treated with radioiodine

From 1969 to 1990 there were 309 patients with differentiated thyroid carcinoma (241 papillary and 68 follicular) treated with radioactive iodine for functioning node metastases alone (n = 191) or distant metastases (n = 118) with or without node metastases. These patients represented 32.7% of 945 patients treated in our institution during the same period. Initial treatment included near-total thyroidectomy and 131I ablation of postsurgical thyroid residue, followed by L-thyroxine suppressive therapy. At the end of follow-up (mean 5.8 years), 146 patients (76.4%) in the group with nodal metastases were considered cured, as assessed by clinical and laboratory evaluation including whole body scan (WBS) and serum thyroglobulin (Tg) levels; 32 patients (16.7%) had persistent disease. Loss of 131I uptake in persistent metastatic lesions occurred in five patients (2.6%), and newly developed distant metastases occurred in eight patients (4.2%). Of the patients with distant metastases, 36.4% were cured by 131I. Distant metastases from papillary carcinomas had a higher cure rate than follicular carcinomas (p < 0.01). The metastases of four patients (5.2%) lost the property to take up radioiodine. Lung and bone metastases detectable by WBS but not by radiography were most likely to be cured by 131I. The overall survival at the end of follow-up was 95.8% in patients with only lymph node metastases and 76.0% in those with distant metastases. Tumor-related deaths were 3.6% and 23.7%, respectively. Our data indicate that 131I therapy is highly effective in the treatment of lymph node metastases from differentiated thyroid carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in radioiodine turnover in patients with autonomous thyroid adenoma treated with percutaneous ethanol injection

In 24 patients with autonomous thyroid adenoma, we studied the hormonal pattern (free thyroxine, free triiodothyronine and thyroid stimulating hormone) and markers of radioiodine turnover before and after nodule ablation with percutaneous ethanol injection. METHODS: The hormonal pattern was studied before treatment and at various intervals after nodule ablation. Changes in radioiodine turnover were studied measuring 131I protein-bound iodine and the biologic half-life of radioiodine in the thyroid (calculated from thyroid uptake at 24 and 48 hr) before and after ethanol treatment. RESULTS: The hormonal pattern was normalized by treatment in all patients and remained normal for the follow-up period. Before treatment, protein-bound 131I was elevated in all patients but 4; after treatment, it normalized in 15 patients with the disappearance of the adenoma on scintigraphy. In the remaining 9 patients with only partial nodule destruction on scintigraphy, protein-bound 131I remained elevated although markedly reduced. Biologic half-life was shortened in 18 of 24 patients before treatment; after treatment, it was normal in 18 of 24 patients (13 of 15 with complete nodule ablation and 5 of 9 with partial ablation). CONCLUSION: Ethanol treatment normalized the hormonal pattern in all patients. Measures of radioiodine turnover were better markers of residual disease in that they normalized in almost all patients with complete nodule ablation, whereas they remained abnormal in a high proportion of patients with incomplete ablation. Thyroid hormones remained normal over a follow-up period of 3-7 yr in all patients.     

131 iodine: medical use. Carcinogenic and genetic effects

131 radioiodine is used for treating patients with thyrotoxicosis and differentiated thyroid carcinoma. Its therapeutic effect is related to the radiation dose delivered to the thyroid tissue. The radiation dose is related to its radioactive concentration (ratio between the radioactive uptake and the mass of functional tissue) and its effective half-life. Follow-up studies of patients exposed to 131I did not demonstrate any tumorigenic effect of 131I on the thyroid gland in adults, but do exclude such an effect in children. The dose delivered to other tissues is relatively low, and significant risk of cancer and leukemia has been found only in patients exposed to high cumulative activities of 131I (> 15 GBq). No genetic effect has been found in the studies of the outcome of pregnancies in women exposed to 131I for thyroid carcinoma. These data indicate that there is no scientific reason to avoid the use of 131I even in young patients when therapeutic benefits can be obtained.     

Quantification of salivary gland function in thyroid cancer patients treated with radioiodine

PURPOSE: Damage to salivary gland function following external irradiation has been documented. However, the extent of damage following radioiodine (131I) therapy for thyroid cancer has not been adequately studied. We evaluated salivary dysfunction in Ca-thyroid patients treated with therapeutic doses of 131I. METHODS AND MATERIALS: A simple acquisition and analysis protocol using 99mTcO4- (pertechnatate) and a gamma camera computer system was planned. The uptake of 99mTcO4- by the salivary glands at 10 min and percent of excretion of 99mTcO4- from the glands in response to a sialogogue (lemon juice) was studied in 33 patients treated with 1.369-38.702 GBq of 131I (Mean = 10.16 GBq, standard deviation = 7.659 GBq) in addition to 14 athyreotic controls. RESULTS: Significant damage to the salivary gland in terms of abnormal percent uptake or excretion was noted in 72.73% of the patients. Forty-eight percent of the patients treated with 131I showed asymmetrical involvement of the salivary complexes as opposed to none of the controls. Reduction in uptake of 99mTc4- or response to sialogogue was dose dependent, being more marked with higher radioiodine doses. Parotid glands were more affected than submandibular glands following 131I therapy. CONCLUSIONS: 131I therapy produces a significant effect on salivary gland function that is dose related and becomes evident over a period of several months after treatment.     

The dexamethasone suppression test and treatment outcome in elderly depressed patients participating in a placebo-controlled multicenter trial involving moclobemide and nortriptyline

A 28-year-old woman was referred to us to undergo 131I therapy who had multiple pulmonary metastases from papillary thyroid carcinoma after total thyroidectomy. There was no increased accumulation of a tracer in the pulmonary metastatic foci on whole-body scanning using a 111 MBq diagnostic dose of 131I. However, the pulmonary metastases were gradually decreased in size, and then clearly reduced 8 months after the start of TSH suppression therapy, which was maintained by T3 instead of T4 to bring down the serum TSH level below 0.1 microU/ml. Reduction rates of the foci were 33-76% on chest X-ray. The reduction was confirmed and no new lesions were found on the serial CT scans. Serum thyroglobulin level was lowered 80 to 25 ng/ml by this suppression therapy and progression of disease was not observed under a 54 months' T3 treatment. Thus, TSH suppression therapy might improve survival of patients with differentiated thyroid cancer.