Efficacy of 131I Therapy

When the DxWBS and neck ultrasonography are both negative, patients are often empirically treated with 131I, both to locate and to treat persistent tumor [4]. Whether this benefits patients has sparked much controversy [12-15], mainly because there are few studies with long-term follow-up of such treatment, there are no randomized prospective trials of this treatment, and there are considerable differences in patient cohorts and endpoints among studies of empiric 131I treatment. Still, there is one consistent observation: serum Tg levels decline when 131I uptake is seen on the RxWBS after 3700 to 5550 MBq (100 to 150 mCi) of 131I,particularly in patients with lung metastases (Figures 20.5 and 20.6) [27,62]. Empiric 131I treatment must be considered with caution, however, in the light of studies that show a slow fall in high serum Tg levels months to years after 131I ablation without further treatment [11,27]. Long-term follow-up of our cohort of patients [6] undergoing follow-up studies showed that about half the patients whose rhTSH-stimulated Tg increased above the detectable range but remained <2 mg/L had a spontaneous fall in serum Tg to undetectable levels over 3 to 5 years, whereas this occurred in only 5% of patients with an rhTSH-stimulated serum Tg >2 mg/L.

Follow-up is too short in most studies to know if empirically treating high serum Tg levels when the DxWBS is negative enhances

Serum Tg Responses in 17 Patients with DTC Empirically Treated with 131I

1000

1 2 3 4 5 6 Evaluations at 6 to 24 Month Intervals after mI Treatment

Mean Tg 74 62 32

Figure 20.5 Serum Tg levels after 131I treatment of thyroid cancer in 17 patients with elevated serum Tg levels and negative DxWBS scans. Evaluations were performed within 1 year of a positive RxWBS and/or Tg measurement greater than 5 mg/L, and 1 to 2 years after a negative RxWBS or Tg measurement of 5 mg/L or less. The amount of 1311 administered at each evaluation ranged from none in some patients to 3700 to 11100MBq (100 to 300 mCi) in others. (Drawn from the data of Pineda et al. [62].)

survival, but several studies suggest that this occurs. The survival benefit from 131I therapy appears to be inversely related to tumor mass. Schlumberger [63], for example, reported complete remission and 10-year survival rates, respectively, of 96% and 100% in 19 patients with tumor found only on a positive RxWBS,

Serum Tg Responses in 17 Patients with DTC Empirically Treated with 131I

131i Therapy

1 2 3 4 5 6 Evaluations at 6 to 24 Month Intervals after mI Treatment

Mean Tg 74 62 32

Figure 20.5 Serum Tg levels after 131I treatment of thyroid cancer in 17 patients with elevated serum Tg levels and negative DxWBS scans. Evaluations were performed within 1 year of a positive RxWBS and/or Tg measurement greater than 5 mg/L, and 1 to 2 years after a negative RxWBS or Tg measurement of 5 mg/L or less. The amount of 1311 administered at each evaluation ranged from none in some patients to 3700 to 11100MBq (100 to 300 mCi) in others. (Drawn from the data of Pineda et al. [62].)

Serum Tg Responses 10 Months after Empiric 131I Treatment of 28 Patients and No Therapy for 32 Patients

Serum Tg Responses 10 Months after Empiric 131I Treatment of 28 Patients and No Therapy for 32 Patients

131i Thyroid Cancer

Figure 20.6 Mean change in serum Tg levels 10 months after empiric 131I therapy of 28 patients with high serum Tg concentrations and negative DxWBS studies compared with 32 control patients who did not undergo 131I therapy for elevated serum Tg concentrations and negative DxWBS. The differences between the two groups are statistically significant (P < 0.001). (Drawn from the data of Koh et al. [68].)

Treated E3 Untreated

Treated E3 Untreated w

Figure 20.6 Mean change in serum Tg levels 10 months after empiric 131I therapy of 28 patients with high serum Tg concentrations and negative DxWBS studies compared with 32 control patients who did not undergo 131I therapy for elevated serum Tg concentrations and negative DxWBS. The differences between the two groups are statistically significant (P < 0.001). (Drawn from the data of Koh et al. [68].)

compared with 83% and 91% among 55 patients with metastases seen on both the DxWBS and RxWBS, and 53% and 63% among 64 patients with micronodules seen on chest X-ray, and with 14% and 11% among 77 patients with macronodules seen on chest X-ray.

In another study [64], 56 patients with DTC were treated with 5550MBq (150mCi) of 131I because of an elevated serum Tg level after THW and a negative 370 MBq 131I (10mCi) DxWBS. After empiric 131I therapy, half had 131I uptake on the RxWBS and half did not. After a median of 4.2 years (0.5 to 13.5 years) and treatment with a median cumulative 131I activity of 150mCi (range 50-650), 64% of the 28 patients with positive RxWBS achieved complete remission defined as a negative RxWBS and a serum Tg <1.5 |mg/L on THST, compared with only 36% of the 28 patients with a negative RxWBS. None of those with a positive RxWBS died of thyroid cancer, whereas 9 without 131I uptake died of cancer, producing a 5-year survival rate of 100% in the former and 76% in the latter (P < 0.001). However, it may be that patients who had no uptake of 131I on the RxWBS had less well-differentiated tumor, which in itself might explain the differences in survival benefit from empiric 131I therapy.

In another study of 23 patients treated with 131I for diffuse pulmonary metastases detected only by 131I imaging, 87% had no lung uptake on subsequent scans [65]. After 131I therapy, serum Tg became undetectable and lung CT scans showed disappearance of the micronodules in almost half the patients, while lung biopsy showed no evidence of disease in two.

Others also report a substantial fall in serum Tg levels after 131I treatment with little or no progression of disease compared with a rise in serum Tg over time and progression of disease in patients who have been treated [62]. Others report a reduction of metastatic disease in most patients whose lung metastases concentrate 131I, but find that a complete remission is uncommon [66,67]. Still, a partial response with reduction of metastatic disease is usually possible and patients generally have a good quality of life with no further disease progression.

In another study [68], in which 28 patients with high serum Tg levels and negative DxWBS studies were treated with 131I and 32 were not treated, the decreases in serum Tg during THST and THW in the treated group were 41.2% and 37.0%, respectively, levels that were significantly higher (P < 0.001) than those in the untreated group,which were 43.6% and 66.6%,respectively (Figure 20.6). The serum Tg levels were undetectable (<1 mg/L) in four cases, both on and off thyroid hormone 15 to 22 months after the administration of 131I, and these negative serum Tg levels persisted for 24 to 70 months; however, this was not observed in any of the untreated group. The RxWBS studies revealed pathologic uptake in 12 of 28 cases (43%). Most of the patients in the treated group (89%) had stable disease or experienced a partial remission, while only 11% had progression of their disease, whereas the comparable figures in the untreated group were, respectively, 53% and 47% (Figure 20.7).

Eleven studies of empiric 131I therapy are summarized in Table 20.1 [13,14,27,62,64,68-73]. In

Figure 20.7 Location of tumor and disease progression in the same group of patients whose data are shown in Figure 20.6. The panel on the left shows the location of 131I uptake in the treated group and the panel on the right shows the effect of therapy in the two groups. (Drawn from the data of Koh et al. [68].)

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