Long-term risks for thyroid cancer and other neoplasms after exposure to radiation

Clinical behavior of radiation-induced thyroid cancer: factors related to recurrence

BACKGROUND

Whether thyroid cancer is more aggressive in radiation-exposed patients is not resolved. The frequency of aggressive features in post-Chernobyl patients suggests this may be the case. Our aim was to address this question by re-examining the pattern of risk factors for recurrence of thyroid cancers found in a cohort exposed to external radiation.

METHODS

The study population was drawn from a cohort of 4296 people, followed since 1974, who were treated before the age of 16 with conventional external radiation for benign conditions of the head and neck between 1939 and the early 1960s. The study group consisted of 390 patients who had surgically verified thyroid cancer. Potential risk factors for recurrence were evaluated by proportional hazards analysis.

RESULTS

Fifty patients had recurrences an average of 8.7 years after diagnosis while the other 340 patients were followed for an average of 19.7 years. The sooner after radiation exposure the cancer occurred, the more likely it was to recur (hazard ratio, 0.96/year; 95% confidence interval [CI] 0.91-0.99). Taking into account the effect of the onset of screening in 1974, the features predictive of recurrence were younger age at the initial diagnosis (hazard ratio, 0.95/year; 95% CI, 0.91-0.99) and the size of the thyroid cancer (hazard ratio, 1.2/cm; 95% CI, 1.0-1.6).

CONCLUSION

Although not based on a direct comparison, we conclude that thyroid cancers following external radiation exposure are not, on average, more aggressive than other thyroid cancers. The similarity of risk factors for recurrence suggests that they should be treated and followed in the same way as non-radiation-induced thyroid cancers.

Cellular distributions of molecules with altered expression specific to thyroid proliferative lesions developing in a rat thyroid carcinogenesis model

To identify differentially regulated molecules related to early and late stages of tumor promotion in a rat two-stage thyroid carcinogenesis model by an antithyroid agent, sulfadimethoxine, microarray-based microdissected lesion-specific gene expression profiling was carried out. Proliferative lesions for profiling were divided into two categories: (i) focal follicular cell hyperplasias (FFCH) and adenomas (Ad) as early lesions; and (ii) carcinomas (Ca) as more advanced. In both cases, gene expression was compared with that in surrounding non-tumor follicular cells. Characteristically, upregulation of cell cycle-related genes in FFCH + Ad, downregulation of genes related to tumor suppression and transcription inhibitors of inhibitor of DNA binding (Id) family proteins in Ca, and upregulation of genes related to cell proliferation and tumor progression in common in FFCH + Ad and Ca, were detected. The immunohistochemical distributions of molecules included in the altered expression profiles were further examined. In parallel with microarray data, increased localization of ceruloplasmin, cyclin B1, and cell division cycle 2 homolog A, and decreased localization of poliovirus receptor-related 3 and Id3 were observed in all types of lesion. Although inconsistent with the microarray data, thyroglobulin immunoreactivity appeared to reduce in Ca. The results thus suggest cell cycling facilitation by induction of M-phase-promoting factor consisting of cyclin B1 and cell division cycle 2 homolog A and generation of oxidative responses as evidenced by ceruloplasmin accumulation from an early stage, as well as suppression of cell adhesion involving poliovirus receptor-related 3 and inhibition of cellular differentiation regulated by Id3. Decrease of thyroglobulin in Ca may reflect dedifferentiation with progression.

Can we reduce the incidence of second primary malignancies occurring after radiotherapy? A critical review

Second primary malignancies (SPMs) occurring after oncological treatment have become a major concern during the past decade. Their incidence has long been underestimated because most patients had a short life expectancy after treatment or their follow-up was shorter than 15 years. With major improvement of long-term survival, longer follow-up, cancer registries and end-result programs, it was found that the cumulative incidence of SPM could be as high as 20% of patients treated by radiotherapy. This cumulative proportion varies with several factors, which ought to be studied more accurately. The delay between irradiation and solid tumor emergence is seldom shorter than 10 years and can be as long as half a century. Thus, inclusion in a cohort of patients with a short follow-up leads to an underestimation of the proportion of SPM caused by treatment, unless actuarial cumulative incidence is computed. The incidence varies with the tissue and organs, the age of the patient at treatment, hereditary factors, but also, and probably mainly, with dose distribution, size of the irradiated volume, dose, and dose-rate. An effort toward a reduction in their incidence is mandatory. Preliminary data suggest that SPMs are mainly observed in tissues having absorbed doses above 2 Gy (fractionated irradiation) and that their incidence increases with the dose. However, in children thyroid and breast cancers are observed following doses as low as 100 mGy, and in adults lung cancers have been reported for doses of 500 mGy, possibly due to interaction with tobacco. The dose distribution and the dose per fraction have a major impact. However, the preliminary data regarding these factors need confirmation. Dose-rates appear to be another important factor. Some data suggest that certain patients, who could be identified, have a high susceptibility to radiocancer induction. Efforts should be made to base SPM reduction on solid data and not on speculation or models built on debatable hypotheses regarding the dose-carcinogenic effect relationship. In parallel, radiation therapy philosophy must evolve, and the aim of treatment should be to deliver the minimal effective radiation therapy rather than the maximal tolerable dose.

Multiplex analysis of cytokines as biomarkers that differentiate benign and malignant thyroid diseases

Thyroid cancer incidence is increasing, and its diagnosis can be challenging. Fine needle biopsy, the principal clinical tool to make a tissue diagnosis, leads to inconclusive diagnoses in up to 30% of the cases, leading to surgery. Advances in proteomics are improving abilities to diagnose malignant conditions using small samples of tissue or body fluids. We hypothesized that analysis of serum growth factors would uncover diagnostically informative differences between benign and malignant thyroid conditions. Using xMAP profiling, we evaluated concentrations of 19 cytokines, chemokines, and growth factors. We used sera from 23 patients with cancer (Malignant group), 24 patients with benign nodular thyroid disease (Benign group), and 23 healthy subjects (Normal group). In univariate analysis, five factors (epithelial growth factor, hepatocyte growth factor, Interleukins-5 and -8, and regulated upon activation, normally T-expressed and presumably secreted (RANTES) distinguished subjects with thyroid disease from the Normal group. In multivariate analysis, the set {Interleukin-8, hepatocyte growth factor, monocyte-induced γ interferon, interleukin-12 p40} achieved noteworthy discrimination between Benign and Malignant groups (area under the receiver operating characteristics curve was 0.81 (95% confidence interval: 0.65-0.90)). Multiplex panels of serum biomarkers may be promising tools to diagnose cancer in patients presenting with evidence of nodular thyroid disease.

Thyroidectomies from patients with history of therapeutic radiation during childhood and adolescence have a unique mutational profile

Radiation in childhood is a known risk factor for thyroid carcinoma, but may also be related to benign nodular hyperplasias. Recent evidence from comparative genomic hybridization indicates that radiation can induce clonal DNA damage in cultured rat thyrocytes. We used a loss of heterozygosity analysis for the loci identified by comparative genomic hybridization to study human thyroids. Thyroids from patients with a history of radiation, patients who had recent therapeutic external beam radiation for laryngeal carcinoma, and patients who had no radiation and underwent incidental thyroidectomy with laryngectomy for laryngeal carcinoma were included. PCR was performed for 18 different genetic loci defined by prior reported comparative genomic hybridization study. A semiquantitative capillary electrophoresis analysis was used and frequency of allelic loss was calculated from the number of losses/the number of informative loci. A total of 40 cases of thyroids from patients with childhood radiation, 12 cases of recently radiated thyroids, and 15 cases of nonradiated thyroids were included. In the nonradiated and recently radiated thyroids, the mean frequency of allelic loss was 2.3%. In the thyroids from patients radiated as children, the mean frequency of allelic loss was 39%. Losses were seen at every locus with a range of 7-100% of the cases analyzed (mean 49.6%). Radiation in childhood was associated with both benign nodular disease and carcinomas of the thyroid. The frequency of allelic loss was very high in all lesions in these patients, as compared to control thyroid glands. These data from human thyroids support prior cell culture experiments and show that radiation induces genetic mutational damage even in benign proliferative processes in these thyroids.

Size, number, and distribution of thyroid nodules and the risk of malignancy in radiation-exposed patients who underwent surgery

CONTEXT

The chance that a thyroid nodule is malignant is higher when there is a history of childhood radiation exposure.

OBJECTIVE

The objective of the study was to determine how the size of a thyroid nodule, the number of nodules, and the distribution of nodules influence the risk of cancer in irradiated patients.

PATIENTS

From a cohort of 4296 radiation-exposed people, we studied the 1059 that underwent thyroid surgery. DESIGN AND OUTCOMES: We studied the association between the size, number, distribution, and rank order of thyroid nodules and the chance of malignancy.

RESULTS

There were 612 malignant nodules in 358 patients and 2037 benign ones in 930 patients. There was no change in the risk that a nodule was malignant with increasing size (odds ratio 0.91/cm, P = 0.11) among the 1709 nodules that were 0.5 cm or greater. A solitary nodule had a similar likelihood of being malignant as a nodule that was one of several (18.8 vs. 17.3%), whereas patients with multiple nodules were more likely to have thyroid cancer than those with solitary nodules [30.7 vs. 18.7%; risk ratio 1.64 (1.27-2.13)]. Aspirating only the largest nodule would have missed 111 of the cancers (42%), whereas aspirating the two largest nodules would have missed 45 of the cases (17%), although none would have been 10 mm or greater.

CONCLUSIONS

In radiation-exposed patients, the following conclusions were made: 1) the likelihood that a nodule is malignant is independent of nodule number and size; 2) the likelihood of cancer is increased if more than one nodule is present; 3) evaluating the two largest nodules by fine-needle aspiration would have resulted in a significant number of cases being missed but none with large cancers; and 4) more than half of the patients with thyroid cancer had multifocal tumors.

Papillary thyroid cancer: monitoring and therapy

The last 10 years have seen a major paradigm shift in the management of thyroid cancer, with greater reliance on serum thyroglobulin and neck ultrasonography, and less emphasis on routine diagnostic whole-body radioactive iodine scanning for detection of recurrent disease. As our follow-up tests become more sensitive for detection of recurrent disease, we are finding many asymptomatic patients who have low-level persistent disease many years after initial therapy that may or may not benefit from additional testing and therapy. These difficult issues have been addressed by at least five different sets of guidelines published recently by various thyroid specialty organizations around the world. In this article, the authors compare and contrast the recommendations from the various guidelines in an attempt to define areas of consensus and explore possible reasons for differing recommendations.

Factors related to the recurrence of thyroid nodules after surgery for benign radiation-related nodules

OBJECTIVE

Benign thyroid nodules are increased by radiation exposure and recurrences are common. The goal of this study was to determine the factors related to recurrence of nodular disease and the efficacy of thyroid hormone therapy in reducing them.

DESIGN, SETTING, AND SUBJECTS

The study population was drawn from a cohort of 4296 people treated before the age of 16 with conventional external radiation for benign conditions of the head and neck between 1939 and the early 1960s. The study group consisted of 632 subjects who had benign nodules removed surgically. At the discretion of their physicians, 426 subjects were treated with thyroid hormone after surgery, 198 were not, and in 8 subjects, thyroid hormone treatment status was unknown.

MAIN OUTCOMES

There were 129 (20.4%) subjects who developed new nodules during follow-up. Women had a greater risk of recurrent nodules than men (27.5% vs. 13.5%) and the rate of recurrence correlated inversely with the extent of surgery. The group who took thyroid hormone had a lower recurrence rate than the untreated group (14.2% vs. 34.2%). The risk of recurrence was reduced to 0.69 (0.47-1.01) in thyroid hormone-treated subjects, regardless of extent of surgery, and to 0.66 (0.46-0.97) when only the subjects with less than 75% of their thyroid removed were considered.

CONCLUSION

Thyroid hormone therapy reduced recurrences in this irradiated cohort. It should be recommended to all patients with irradiated thyroids and previous thyroid surgery.