Iodine-131 Therapy in Cases with Metastatic Well-differentiated Thyroid Cancer

Author(s)：

Katsuyuki Karasawa, Takuya Shimizuguchi, Hiroto Murata, Shun'ichiro Kageyama, Hiroshi Tanaka, Yumiko Machitori, Motoaki Fujii, Keiji Nihei

Affiliation(s)：

Dept. of Radiology, Tokyo Metropolitan Cancer and Infectious diseases Center Komagome Hospital

Purpose/Objective: Various therapeutic options are available for metastatic well-differentiated thyroid cancer, such as thyroid stimulating hormone (TSH) suppression therapy, iodine-131 therapy, external beam radiation therapy, surgery, chemotherapy, and so on. Iodine-131 therapy, one of the conservative systemic therapies, is helpful when the tumor is avid for iodine. Although iodine-131 is often administrated for patients with advanced thyroid cancer, its survival benefit is still controversial. Therefore, we performed this single institution retrospective study.

Materials/Methods: We reviewed the medical records of patients who were treated with iodine-131 in our hospital from 1995 to 2009. A total of 462 patients were identified. Among them 242 had metastatic lesions at the time of initial iodine-131 therapy. The patient's characteristics were as follows, age: 14-83 (median 62), male / female: 89 / 153, the site of metastasis: pulmonary only / osseous metastasis / other: 132 / 81 / 29. Pathologic category: follicular / papillary / others: 76 / 134 / 32. We usually prescribed 100mCi of iodine-131 in one course of therapy (range: 30-200mCi) and repeated every 6 to 12 months when thought to be beneficial. Overall treatment sessions ranged from 1 to 13 times with an average of 1.7 times. Median overall amount of iodine-131 was 200mCi (range: 60-1300mCi). Median follow-up period was 47months.

Results: One hundred and twenty-two patients (50.4%) confirmed iodine-131 concentration in metastatic lesion. Follicular carcinoma was significantly more avid iodine-131 than papillary carcinoma (86% vs. 30% p<0.0001). The 5-year and 10-year overall survival rate for overall patients was 69.8%, 54.0% respectively. Overall median survival time (MST) was 10.2 years. The 10-year survival rate was 81.4% in patients less than or equal to 45 years old, and 48.2% in patients over 45 years old (p=0.0007). The 10-year survival rate in patients with only pulmonary metastasis, with osseous metastasis was 70.1%, 39.5% respectively (p=0.00013). Gender, histological subtype, iodine-131 concentration was not a significant prognostic factor. For patients with only pulmonary metastasis, 10-year overall survival rate was 79.9% for iodine-131 concentrating metastasis, and 59.4% for non-concentrating metastasis (p=0.055). For cases with bone metastases, 5-year survival rate and MST for cases with or without iodine-131 concentration were 59% and 7.8 years, 28% and 3.2 years, respectively (p=0.0007). Among cases with iodine-131 concentrating metastasis, 5-year survival rate for those cases without metastases to other organs was 76%, whereas it was 17% for those with metastases to other organs (p<0.0001).

Conclusions: Follicular carcinoma had significantly high ability of iodine uptake. Young age and patients with metastasis limited to the lung, are favorable prognostic factors. Patients with only pulmonary metastasis treated for iodine-131 concentrating metastasis tended to gain survival benefit by this therapy. Among patients with bone metastasis treated for iodine-131 concentrating metastasis significantly gained survival benefit by this therapy than those with non-concentrating bone metastases. Also, among patients with iodine-131 concentrating bone metastases, patients with bone metastases alone survived better than those with other organ metastases. Our results suggested the possibility that iodine-131 might improve the survival outcome in certain group of patients even though TSH suppression therapy works well.