Leukaemias and cancers following iodine-131 administration for thyroid cancer

Abstract

Summary We studied 1771 patients treated for a thyroid cancer in two institutions. None of these patients had been treated with external radiotherapy and 1497 had received 1311. The average 1311 cumulative activity administered was 7.2 GBq, and the estimated average dose was 0.34 Sv to the bone marrow and 0.80. Sv to the whole body. After a mean follow-up of 10 years, no case of leukaemia was observed, compared with 2.5 expected according to the coefficients derived from Japanese atomic bomb survivors (P = 0.1). A total of 80 patients developed a solid second malignant neoplasm (SMN), among whom 13 developed a colorectal cancer. The risk of colorectal cancer was found to be related to the total activity of 1311 administered 5 years or more before its diagnosis (excess relative risk = 0.5 per GBq, P = 0,02).These findings were probably caused by the accumulation of 1311 in the colon lumen. Hence, in the absence of laxative treatment, the dose to the colon as a result of 1311 administered for the treatment of thyroid cancer could be higher than expected from calculation of the International Commission on Radiological Protection (ICRP). When digestive tract cancers were excluded, the overall excess relative risk of second cancer per estimated effective sievert received to the whole body was -0.2 (P = 0.6).Keywords: radiocarcinogenesis; carcinogenic effects of 1311; protracted exposure to radiation; thyroid cancer On account of the small population dose involved, published studies (IARC, 1994) of nuclear industry workers do not have sufficient power to make reliable comparisons with the risks estimated from the Japanese atomic bomb survivors (UNSCEAR, 1994). Hence, studies of adult populations undergoing protracted exposure to radiation for medical reasons are still necessary. For this purpose, '3'I is a suitable model, because its physical halflife is 8 days. The risks of solid tumours and leukaemia after administration of '3'I have been studied in several cohorts of adults (Hall et al 1991(Hall et al , 1992 Dottorini et al, 1995); nevertheless, the statistical power of these studies is still insufficient to derive precise coefficients.Another reason for studying the carcinogenic effects of '3'I is the fact that considerable amounts of various radioisotopes of iodine, including '3'I, were released in the atmosphere during the Chernobyl accident. A substantial increase in thyroid cancer incidence has been observed in children living in the most heavily contaminated areas at the time of the accident (Stsjazhko et al. 1995), but no increased incidence of other malignancies, including leukaemia, has been reported so far. More data are thus needed to predict future risks in populations that have been contaminated.We report the results of a study of 1771 patients treated for a thyroid cancer, of whom 651 had received 1311 for diagnosis, and 846 for therapy. Among the 2479 patients, 173 patients were excluded because they had died or were lost to follow-up during the first two years after the diagnosis of thyroid cancer; ...

Second primary malignancies in thyroid cancer patients

“…The excess of colorectal cancer was previously evidenced only in the French cohort (de Vathaire et al, 1997), and the excess of salivary gland cancer was found in the Swedish (Hall et al, 1991) and Italian (Dottorini et al, 1995) cohorts. In contrast, the excess of bone and soft-tissue cancers following 131 I administration has not been previously reported.…”

“…Patients with a malignancy prior to thyroid cancer, with a second malignancy within the first 2 years of follow-up, or dying within 2 years of diagnosis were excluded. The treatment modalities in each cohort have been described previously (Hall et al, 1991;Dottorini et al, 1995;de Vathaire et al, 1997).…”

“…However, the late health effects associated with 131 I given as treatment for thyroid cancer are difficult to assess since the number of thyroid cancer patients treated at each centre is comparatively small. To date, the impact of 131 I on the occurrence of SPM in thyroid cancer patients has been studied in only three large cohorts (Hall et al, 1991;Dottorini et al, 1995;de Vathaire et al, 1997). In an effort to obtain a more accurate quantification of the overall risk of SPM, a pooled analysis of these three cohorts was performed and follow-up data were extended beyond the original publications.…”

Implications of mediastinal uptake of 131I with regard to surgery in patients with differentiated thyroid carcinoma

“…14,15 Furthermore, in several reported instances, posttreatment WBS has revealed mediastinal 131 I activity that, on subsequent surgical exploration, was found to be attributable to physiologic enlargement of the thymus. 5,16 -20 Without appropriate guidelines, it is difficult to obtain a consensus regarding diagnostic and therapeutic strategies for patients with mediastinal uptake of 131 I.…”

Follicular carcinoma thyroid presenting as skull metastasis: a rare case report

“…Also, high doses of radioactive iodine have been linked to an increased risk of leukaemias as well as bone, soft tissue, colorectal, and salivary gland cancers. 12 Radiation induced pulmonary fibrosis in patients with pulmonary metastases after repeated I-131 doses is also a potential risk, albeit rarely reported. In addition to thyroidectomy and I-131 treatment, studies also support the use of external beam radiation therapy (EBRT) for locoregional control of inoperable metastases.…”