Outcome of differentiated thyroid cancer with detectable serum Tg and negative diagnostic I-131 whole body scan: Comparison of patients treated with high I-131 activities versus untreated patients

Detectable serum Tg levels associated with negative diagnostic I-131 whole body scan are not infrequently found in patients with differentiated thyroi d cancer. Several researchers have shown that in these patients the adminis tration of high I-131 activity (100 mCi or more) increases the sensitivity of a posttherapy diagnostic I-131 whole body scan performed a few days late r and allows the detection of neoplastic foci not seen with diagnostic dose s of I-131. Empirical radioiodine treatment has also been advocated by some researchers, but its therapeutic effect is controversial. In our institute, positive serum Tg/negative diagnostic I-131 whole body sc an patients were not treated with high I-131 activities before 1984; afterw ard, almost all patients with positive serum Tg/negative diagnostic I-131 w hole body scan patients were treated with radioiodine, and a posttherapy di agnostic I-131 whole body scan was performed. In the present retrospective study we compared the outcome of these two groups of patients, 42 treated a nd 28 untreated, followed for mean periods of 6.7 +/- 3.8 and 11.9 +/- 4.4 yr, respectively. In the treated group the first posttherapy diagnostic I-1 31 whole body scan was negative in 12 patients and positive in 30 patients. I-131 treatment was further administered only in the latter group. At the end of follow-up in treated patients a complete remission (normaliza tion of serum Tg off L-thyroxine and negative diagnostic I-131 whole body s can) was observed in 10 patients (33.3%). In 9 cases (30%) posttherapy diag nostic I-131 whole body scan became negative, and serum Tg was reduced but still detectable; in 11 patients (36.6%) serum Tg was detectable, and postt herapy diagnostic I-131 whole body scan was positive. The resolution of I-1 31 uptake in lung metastases was observed in 8 of 9 cases (88.8%) and in ce rvical node metastases in 11 of 18 cases (61.1%). In patients treated only once because the posttherapy diagnostic. I-131 whole body scan was negative (n = 12), 2 patients (16.7%) were in apparent remission, 7 (58.3%) had det ectable Tg values without evidence of disease, 2 (16.7%) showed lymph node metastases in the mediastinum, and 1 patient (8.3%) died because of lung me tastases. Of the 28 untreated patients, none with radiological evidence of disease, s erum Tg off L-thyroxine therapy became undetectable in 19 cases (67.9%), si gnificantly reduced in 6 cases (21.4%), and unchanged or increased in 3 pat ients (10.7%), 1 of whom developed lung metastases 14 yr after the diagnosi s. In summary, our results indicate that in patients with detectable serum Tg and negative diagnostic I-131 whole body scan, treatment with high doses of I-131 may have therapeutic utility in patients with lung metastases and, t o a lesser extent, in those with lymph node metastases. However, in view of the frequent normalization of Tg values in untreated patients, we believe that treatment with I-131 should be considered according to the result of t he first posttherapy scan. If positive in the lung, I-131 treatment should be continued up to total remission; surgical treatment should be preferred in patients with node metastases, and no treatment should be used in those with thyroid bed uptake or no uptake.