Radiotherapy for primary thyroid cancer as a risk factor for second primary cancers

Association of Definitive Radiotherapy for Esophageal Cancer and the Incidence of Secondary Head and Neck Cancers: A SEER Population-Based Study

Background

Impact of radiotherapy (RT) for esophageal cancer (EC) patients on the development of secondary head and neck cancer (SHNC) remains equivocal. The objective of this study was to investigate the link between definitive RT used for EC treatment and subsequent SHNC.

Methods

This study was conducted using the Surveillance, Epidemiology, and End Results (SEER) database to collect the data of primary EC patients. Fine-Gray competing risk regression and standardized incidence ratio (SIR) and propensity score matching (PSM) method were used to match SHNC patients with only primary head and neck cancer (HNC) patients. Overall survival (OS) rates were applied by Kaplan-Meier analysis.

Results

In total, 14,158 EC patients from the SEER database were included, of which 9,239 patients (65.3%) received RT and 4,919 patients (34.7%) received no radiation therapy (NRT). After a 12-month latency period, 110 patients (1.2%) in the RT group and 36 patients (0.7%) in the NRT group experienced the development of SHNC. In individuals with primary EC, there was an increased incidence of SHNC compared to the general US population (SIR = 5.95, 95% confidence interval (CI): 5.15 - 6.84). Specifically, the SIR for SHNC was 8.04 (95% CI: 6.78 - 9.47) in the RT group and 3.51 (95% CI: 2.64 - 4.58) in the NRT group. Patients who developed SHNC after RT exhibited significantly lower OS compared to those after NRT. Following PSM, the OS of patients who developed SHNC after RT remained significantly lower than that of matched patients with only primary HNC.

Conclusion

An association was discovered between RT for EC and increased long-term risk of SHNC. This work enables radiation oncologists to implement mitigation strategies to reduce the long-term risk of SHNC in patients who have received RT following primary EC.

Out-of-Field Dose Measurement by TLD Dosimetry and Estimation of Radiation-Induced Secondary Cancer Risk of Thyroid and Breast from Head Radiotherapy

Background

Radiation therapy, the most common form of cancer treatment, can result in late complications, such as secondary breast and thyroid cancers.

Objective

This study aimed to evaluate the risk of secondary cancers using two radiobiological models of Excess Absolute Risk (EAR) and Excess Relative Risk (ERR) in patients with brain cancer undergoing radiotherapy for improved survival rates of cancer patients.

Material and Methods

In this expository cross-sectional study, 45 patients under the age of 40 years underwent Whole Brain Radiotherapy (WBRT) using a compact accelerator in Shahid Ramezanzadeh Hospital, Yazd, Iran. Out-of-field organ dose measurement was performed using a Thermoluminescent Dosimeter (TLD) to determine the dose to thyroid and breast tissues. The risk of secondary cancers in these organs was calculated 3, 5, 10, 15, and 20 years after radiation therapy.

Results

The mean values of thyroid cancer risk in men and women were 0.418±0.509 and 0.274±0.306, respectively. ERR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women undergoing radiation therapy were 1.084±2.938, 0.594±1.407, 0.248±0.497, 0.138±0.248, and 0.091±0.148, respectively. EAR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women following radiation therapy were 0.064±0.060, 0.077±0.071, 0.119±0.100, 0.178±0.248, and 0.259±0.178, respectively.

Conclusion

After irradiation, the risk of secondary cancer is affected by factors, such as the patient's age and gender. The secondary thyroid cancer is higher than that of other organs, such as the breast, in the patients undergoing WBRT.

Risk of second primary lung cancer in patients with thyroid cancer: a meta-analysis based on big population studies

BACKGROUND

Previous studies have revealed that the number of cancer survivors developing a second primary malignancy is increasing, especially among thyroid cancer patients, and lung cancer is still the main cause of cancer death. Therefore, we aimed to investigate the risk of second primary lung cancer (SPLC) in patients with thyroid cancer.

METHODS

We searched the PubMed, Web of Science, Embase, and Scopus databases up to November 24, 2021, for relevant research and merged the standardized incidence ratios (SIRs) and 95% confidence intervals (95% CIs) to evaluate the risk of developing SPLC in patients with thyroid cancer.

RESULTS

Fourteen studies involving 1480,816 cases were included in our meta-analysis. The pooled result demonstrated that thyroid cancer patients may have a higher risk of SPLC than the general population (SIR = 1.21, 95% CI: 1.07-1.36, P < 0.01, I2 = 81%, P < 0.01). Subgroup analysis stratified by sex indicated that female patients may have a markedly higher risk of SPLC than male patients (SIR = 1.65, 95% CI: 1.40-1.94, P < 0.01, I2 = 75%, P < 0.01).

CONCLUSIONS

Thyroid cancer patients are more likely to develop SPLC than the general population, especially women. However, other risk factors must be investigated, and more prospective studies are needed to confirm our results.Registration: International Prospective Register of Systematic Reviews: No. CRD42021285399.

Breast Cancer After Treatment of Differentiated Thyroid Cancer With Radioiodine in Young Females: What We Know and How to Investigate Open Questions. Review of the Literature and Results of a Multi-Registry Survey

Published studies on the risk of radiation-induced second primary malignancy (SPM) after radioiodine treatment (RAI) of differentiated thyroid cancer (DTC) refer mainly to patients treated as middle-aged or older adults and are not easily generalizable to those treated at a younger age. Here we review available literature on the risk of breast cancer as an SPM after RAI of DTC with a focus on females undergoing such treatment in childhood, adolescence, or young adulthood. Additionally, we report the results of a preliminary international survey of patient registries from academic tertiary referral centers specializing in pediatric DTC. The survey sought to evaluate the availability of sufficient patient data for a potential international multicenter observational case-control study of females with DTC given RAI at an early age. Our literature review identified a bi-directional association of DTC and breast cancer. The general breast cancer risk in adult DTC survivors is low, ~2%, slightly higher in females than in males, but presumably lower, not higher, in those diagnosed as children or adolescents than in those diagnosed at older ages. RAI presumably does not substantially influence breast cancer risk after DTC. However, data from patients given RAI at young ages are sparse and insufficient to make definitive conclusions regarding age dependence of the risk of breast cancer as a SPM after RAI of DTC. The preliminary analysis of data from 10 thyroid cancer registries worldwide, including altogether 6,449 patients given RAI for DTC and 1,116 controls, i.e., patients not given RAI, did not show a significant increase of breast cancer incidence after RAI. However, the numbers of cases and controls were insufficient to draw statistically reliable conclusions, and the proportion of those receiving RAI at the earliest ages was too low.In conclusion, a potential international multicenter study of female patients undergoing RAI of DTC as children, adolescents, or young adults, with a sufficient sample size, is feasible. However, breast cancer screening of a larger cohort of DTC patients is not unproblematic for ethical reasons, due to the likely, at most slightly, increased risk of breast cancer post-RAI and the expected ~10% false-positivity rate which potentially produced substantial "misdiagnosis."

Cancer risk assessment in modern radiotherapy workflow with medical big data

Modern radiotherapy (RT) is being enriched by big digital data and intensive technology. Multimodality image registration, intelligence-guided planning, real-time tracking, image-guided RT (IGRT), and automatic follow-up surveys are the products of the digital era. Enormous digital data are created in the process of treatment, including benefits and risks. Generally, decision making in RT tries to balance these two aspects, which is based on the archival and retrieving of data from various platforms. However, modern risk-based analysis shows that many errors that occur in radiation oncology are due to failures in workflow. These errors can lead to imbalance between benefits and risks. In addition, the exact mechanism and dose-response relationship for radiation-induced malignancy are not well understood. The cancer risk in modern RT workflow continues to be a problem. Therefore, in this review, we develop risk assessments based on our current knowledge of IGRT and provide strategies for cancer risk reduction. Artificial intelligence (AI) such as machine learning is also discussed because big data are transforming RT via AI.

The Breast-Thyroid Cancer Link: A Systematic Review and Meta-analysis

Rates of thyroid cancer in women with a history of breast cancer are higher than expected. Similarly, rates of breast cancer in those with a history of thyroid cancer are increased. Explanations for these associations include detection bias, shared hormonal risk factors, treatment effect, and genetic susceptibility. With increasing numbers of breast and thyroid cancer survivors, clinicians should be particularly cognizant of this association. Here, we perform a systematic review and meta-analysis of the literature utilizing PubMed and Scopus search engines to identify all publications studying the incidence of breast cancer as a secondary malignancy following a diagnosis of thyroid cancer or thyroid cancer following a diagnosis of breast cancer. This demonstrated an increased risk of thyroid cancer as a secondary malignancy following breast cancer [OR = 1.55; 95% confidence interval (CI), 1.44-1.67] and an increased risk of breast cancer as a secondary malignancy following thyroid cancer (OR = 1.18; 95% CI, 1.09-1.26). There is a clear increase in the odds of developing either thyroid or breast cancer as a secondary malignancy after diagnosis with the other. Here, we review this association and current hypothesis as to the cause of this correlation.

Associations between Medical Conditions and Breast Cancer Risk in Asians: A Nationwide Population-Based Study in Taiwan

Background

The breast cancer incidence in Asia is rising. To explore whether the etiology of breast cancer is different from the known risk factors from studies in Western countries, we conducted a nested case-control study using data from the Taiwan National Health Insurance Research Database (NHIRD).

Methods

All medical conditions based on the first three digits of the ICD-9 and a list of medical conditions based on literature review were retrieved for each case and control. The odds ratios (OR) and 95% confidence intervals (CI) of the associations between medical conditions and breast cancer risks were estimated using conditional logistic regression and adjusted for occupation, number of breast cancer screening, and the average number of outpatient visits prior the diagnosis. The associations were also estimated for younger (<50 years old) and older subjects separately.

Results

The analyses included 4,884 breast cancer cases and 19,536 age-matched controls. Prior breast diseases (OR, 95% CI: 2.47, 2.26–2.71), obesity (1.43, 1.04–1.96), endometriosis (1.44, 1.15–1.80), uterine leiomyoma (1.20, 1.03–1.40), hypertensive diseases (1.14, 1.05–1.25), and disorders in lipid metabolism (1.13, 1.04–1.24) were associated with increased breast cancer risk. No heterogeneity was observed between age groups (<50 and ≥50 years old).

Conclusions

In addition to benign breast diseases, obesity, endometriosis, uterine leiomyoma, hypertensive diseases, and disorders of lipid metabolism were associated with a subsequent breast cancer risk.

Impacts

Our results suggest that estrogen related factors may play an important role in breast cancer risks in the Taiwanese female population.

A new computational model for human thyroid cancer enhances the preoperative diagnostic efficacy

Considering the high rate of missed diagnosis and delayed treatments for thyroid cancer, an effective systematic model for the differential diagnosis is highly needed. Thus we analyzed the data on the clinicopathological characteristics, routine laboratory tests and imaging examinations in a cohort of 13,980 patients with thyroid cancer to establish a new diagnostic model for differentiating thyroid cancer in clinical practice. Here, we randomly selected two-thirds of the population to develop the thyroid malignancy risk scoring system (TMRS) for preoperative differentiation between thyroid cancer and benignant thyroid diseases, and then validated its differential diagnostic power in the rest one-third population. The 18 predictors finally enrolled in the TMRS included male gender, clinical manifestations (fever, neck sore, neck lump, palpitations or sweating), laboratory findings (TSH>1.56mIU/L, FT3>5.85pmol/L, TPOAb>14.97IU/ml, TgAb>48.00IU/ml, Tg>34.59μg/L, Ct>64.00ng/L, and CEA>0.41μg/L), and ultrasound features (tumor number≤ 23mm, site, size, echo texture, margins, and shape of neck lymphnodes). The TMRS is validated to be well-calibrated (P = 0.437) and excellently discriminated (AUC = 0.93, 95% CI [0.92, 0.94]), with an accuracy of 83.2%, a sensitivity of 89.3%, a specificity of 81.5%, positive and negative predictive values of 56.8% and 96.6%, positive and negative likelihood ratios of 4.83 and 0.13 in the development cohort, respectively. The TMRS highlights that this differential diagnostic system could help provide accurate preoperative risk stratification for thyroid cancer, and avoid unnecessary over- and under-treatment for such patients.

Association of thyroid diseases with primary extra-thyroidal malignancies in women: results of a cross-sectional study of 6,386 patients

We here analyzed the prevalence of extra-thyroidal malignancies (EM) in 6,386 female patients affected by different thyroid disease (TD). At first, an age-matched analysis of EM in all patients was performed. We then evaluated EM prevalence in four TD diagnostic categories: non-nodular TD (n = 2,159); solitary nodule (n = 905); multinodular TD (n = 2,871); differentiated thyroid cancers (n = 451). Finally, patients were grouped based on the absence (n = 3,820) or presence of anti-thyroglobulin (TgAb) and/or anti-thyroperoxidase (TPOAb) (n = 2,369), or anti-Thyroid Stmulating Hormone (TSH) receptor autoantibodies (n = 197). A total of 673 EM were recorded. EM prevalence in TD patients was higher compared to the general population (Odds Ratio, OR 3.21) and the most frequent EM was breast cancer (OR 3.94), followed by colorectal (OR 2.18), melanoma (OR 6.71), hematological (OR 8.57), uterus (OR 2.52), kidney (OR 3.40) and ovary (OR 2.62) neoplasms. Age-matched analysis demonstrated that the risk of EM was maximal at age 0-44 yr (OR 11.28), remaining lower, but significantly higher that in the general population, in the 45-59 and 60-74 year age range. Breast and hematological malignancies showed an increased OR in all TD, while other cancers associated with specific TD. An increased OR for melanoma, breast and hematological malignancies was observed in both TPOAb and/or TgAb autoantibody negative and positive patients, while colorectal, uterus, kidney and ovary cancers showed an increased OR only in thyroid autoantibody negative patients. In conclusions, women affected by both benign and malignant TD, especially at a younger age and in absence of thyroid autoimmunity, have an increased risk of developing primary EM, thus requiring a careful follow-up and surveillance.

Second primary malignancies following thyroid cancer: a population-based study in Taiwan

OBJECTIVE

Most studies on second primary malignancies (SPMs) after primary thyroid cancer were conducted in USA or Europe. The discrepancy between SPMs in these studies could be attributed to geographical and ethnic heterogeneity. Thus, there is a clear need for another large-scale epidemiological study, particularly in Asian countries, to define the incidence and risk of SPMs in thyroid cancer survivors.

DESIGN

A population-based study was conducted using the nation-wide database from Taiwan Cancer Registry between 1979 and 2006.

METHODS

We quantified standardized incidence ratios (SIRs) and cumulative incidence of SPMs among 19,068 individuals (4205 males and 14,863 females) with primary thyroid cancer.

RESULTS

A total of 644 cases (3.38%) developed at least a SPM during 134,678 person-years of follow-up. The risk for subsequent SPMs was significantly greater than that of the general population (SIR=1.33, 95% CI 1.23-1.44). There was a greater risk of developing major salivary glands, nasopharyngeal, lung, thymus, breast (females), bladder, and brain cancers, and leukemia and lymphoma. We observed that the risk was highest within the first 5 years of diagnosis of thyroid cancer (SIR=5.29, 1.68, and 0.68 for ≤ 5, 5-10, and >10 respectively) and in the younger patients (SIR=1.81 vs 1.61 for <50 and ≥ 50 respectively). The median overall survival for primary thyroid cancer patients was 23.28 years, but it was only 4.73 years for those who developed SPMs.

CONCLUSION

Thyroid cancer is associated with a 33% risk increment of SPMs, which had a negative impact on survival. There are sites of SPMs in the Asian population that are distinctive from those in the Western population, suggesting that other genetic predisposition or environmental factors may play a role.

The risk of second cancers after diagnosis of primary thyroid cancer is elevated in thyroid microcarcinomas

BACKGROUND

Thyroid cancers have increased dramatically over the past few decades. Comorbidities may be important, and previous studies have indicated elevated second cancer risk after initial primary thyroid cancers. This study examined the risk of second cancers after development of a thyroid cancer, primary utilizing the Surveillance, Epidemiology, and End Results (SEER) program database.

METHODS

The cohort consisted of men and women diagnosed with first primary thyroid cancer who were reported to a SEER database in 1973-2008 (n=52,103). Standardized incidence ratios (SIR) were calculated for all secondary cancers. Confidence intervals and p-values are at 0.05 significance alpha level and are two-sided based on Poisson exact methods.

RESULTS

In this cohort, 4457 individuals developed second cancers. The risk of developing second cancers after a primary thyroid cancer varied from 10% to 150% depending on different cancer types. Cancers in all sites, breast, skin, prostate, kidney, brain, salivary gland, second thyroid, lymphoma, myeloma, and leukemia were elevated. The magnitude of the risk varied by histology, tumor size, calendar year of first primary thyroid cancer diagnosis, and the treatment of the primary thyroid cancer. The risk of a second cancer was elevated in patients whose first primary thyroid carcinomas were small, or were diagnosed after 1994, or in whom some form of radiation treatment was administered.

CONCLUSIONS

This large population-based analysis of second cancers among thyroid cancer patients suggests that there was an increase of second cancers in all sites, and the most commonly elevated second cancers were the salivary gland and kidney. Additionally, the increase in second cancers in patients with recently diagnosed thyroid microcarcinomas (<10 mm) suggests that aggressive radiation treatment of the first primary thyroid cancer, the environment, and genetic susceptibility, may increase the risk of a second cancer.

Risk of second primary cancer after treatment for esophageal cancer: a pooled analysis of nine cancer registries

The introduction of new treatments for esophageal cancer including surgery, chemotherapy, radiotherapy, or a combination of these modalities has not only improved patient survival, but may also increase the risk of the second primary cancers. The available evidence is conflicting with most risk estimates based on sparse numbers. Here we estimated standardized incidence ratios (SIRs) of second cancer among 24,557 esophageal cancer survivors (at least 2 months) in the Surveillance, Epidemiology, and End Results (SEER) Program between 1973 and 2007, who had been followed up for median 6.5 years (range 2 months-29.3 years). Second cancer risk was statistically significantly elevated (SIR = 1.34, 95% confidence interval [CI]= 1.25-1.42) among the survivors compared with the general population; the SIRs for cancers of oral and pharynx, stomach, small intestine, larynx, lung and bronchus, thyroid and prostate cancer were 8.64 (95% CI = 7.36-10.07), 2.87 (95% CI = 2.10-3.82), 3.80 (95% CI = 1.82-7.00), 3.19 (95% CI = 2.12-4.61), 1.68 (95% CI = 1.46-1.93), 2.50 (95% CI = 1.25-4.47), and 0.77 (95% CI = 0.65-0.90), respectively. Radiotherapy raised cancer risk of larynx (SIR = 3.98, 95% CI = 2.43-6.14) and thyroid (SIR = 3.57, 95% CI = 1.54-7.03) among all esophageal cancer survivors. For patients who had 5-9 years of follow up after radiotherapy, the SIR for lung cancer was 3.46 (95% CI = 2.41-4.82). Patients with esophageal cancer are at increased risks of second cancers of oral and pharynx, larynx, lung, and thyroid, while at a decreased risk for prostate cancer. These findings indicate that radiotherapy for esophageal cancer patients may increase risk of developing second cancers of larynx, lung, and thyroid. Thus, randomized clinical trials to address the association of radiotherapy and the risk of secondary cancer are warranted.

Risk of subsequent primary thyroid cancer after another malignancy: latency trends in a population-based study

PURPOSE

To evaluate the risk of a subsequent primary thyroid cancer (SPTC) in patients with common invasive cancers, with attention to latency trends and histology associations.

METHODS

Patients with one of 10 common invasive cancers were followed from 1975 to 2008 in 9 registries participating in the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database. Standardized incidence ratios (SIRs) for SPTC were determined by the multiple primary-SIR program in SEER*Stat.

RESULTS

A total of 2502 SPTCs were observed. Greatly elevated SIRs for SPTC were noted for 9 of 10 evaluated cancers in the 12 months after initial diagnosis. The SIRs remained elevated 12-59 months after diagnosis for all cancers except leukemia, uterine, and bladder cancers. Increased risks persisted 60-119 months beyond diagnosis for renal (SIR 2.56) and breast cancer (SIR 1.16); and 120+ months for renal cancer (SIR 2.46). Increased SPTC risk after renal and female breast cancers was mostly seen in nonirradiated patients. The principal histology association was between papillary thyroid cancer and renal cell carcinomas.

CONCLUSIONS

Many common cancers are associated with increased risk of SPTC beyond 12 months of initial diagnosis. Although this can be explained partly by continued surveillance bias, radiation effects, and known rare familial associations for some tumors, these factors alone are unlikely to explain the persistent, significant two-way association with renal and breast cancers. Additional research is needed to further define the biological and environmental mechanisms underlying these associations.

Targeting of tumor radioiodine therapy by expression of the sodium iodide symporter under control of the survivin promoter

To test the feasibility of using the survivin promoter to induce specific expression of sodium/iodide symporter (NIS) in cancer cell lines and tumors for targeted use of radionuclide therapy, a recombinant adenovirus, Ad-SUR-NIS, that expressed the NIS gene under control of the survivin promoter was constructed. Ad-SUR-NIS mediating iodide uptake and cytotoxicity was performed in vitro. Scintigraphic, biodistribution and radioiodine therapy studies were performed in vivo. PC-3 (prostate); HepG2 (hepatoma) and A375 (melanoma) cancer cells all exhibited perchlorate-sensitive iodide uptake after infection with Ad-SUR-NIS, ∼50 times higher than that of negative control Ad-CMV-GFP-infected cells. No significant iodide uptake was observed in normal human dental pulp fibroblast (DPF) cells after infection with Ad-SUR-NIS. Clonogenic assays demonstrated that Ad-SUR-NIS-infected cancer cells were selectively killed by exposure to ¹³¹I. Ad-SUR-NIS-infected tumors show significant radioiodine accumulation (13.3±2.85% ID per g at 2 h post-injection), and the effective half-life was 3.1 h. Moreover, infection with Ad-SUR-NIS in combination with ¹³¹I suppressed tumor growth. These results indicate that expression of NIS under control of the survivin promoter can likely be used to achieve cancer-specific expression of NIS in many types of cancers. In combination with radioiodine therapy, this strategy is a possible method of cancer gene therapy.

Radiation-induced leukemia among children aged 0-5 years at the time of the Chernobyl accident

This case-control study was conducted to estimate the radiation-induced risk of acute leukemia during the period from 1987 to 1997 among residents 0-5 years of age at the time of the Chernobyl accident in the most radioactively contaminated territories of the Ukraine (Rivno, Zhytomyr, Chernihiv and Cherkasy regions). Data were collected from 246 leukemia cases diagnosed between 1 January, 1987, and 31 December, 1997. Each case was verified and interviewed. Verified cases were compared to 492 randomly selected controls matched by age, sex, type of settlement (rural, semirural and urban) and administrative region of residency. The cumulative level of radiation exposure from the time of the Chernobyl accident to the date of diagnosis was assessed for each case and corresponding controls. Four dose-range groups were selected for statistical analysis (0-2.9, 3-9.9, 10-99.9 and 100-313.3 mGy). The risk of leukemia was significantly increased (-2.4 [95%CI: 1.4-4.0]) among those with radiation exposure doses higher than 10 mGy (p = 0.01). The association between radiation exposure and risk was stronger among males (-2.8 [95%CI: 1.4-5.5, p = 0.01]), and for cases of acute leukemia that were diagnosed during the period from 1987 to 1992 (-2.5 [95%CI: 1.2-5.1, p = 0.05]), particularly acute myeloid leukemia (-5.8 [95%CI: 1.4-24.6, p = 0.05]). The influence of possible confounders and methods of selecting controls on the leukemia risk assessment was analyzed. The evaluated risk per unit dose is discussed.

Second primary malignancy risk after radioactive iodine treatment for thyroid cancer: a systematic review and meta-analysis

BACKGROUND

The risk of second primary malignancies (SPMs) associated with cancer therapies is an important concern of thyroid cancer survivors and physicians. Our objective was to determine if the risk of SPMs is increased in individuals with thyroid cancer treated with radioactive iodine (RAI), compared to those not treated with RAI.

METHODS

We performed a systematic review of the literature and meta-analysis. Two independent reviewers screened citations and reviewed full-text papers. If not reported by the primary authors, the relative risk (RR) of SPMs was calculated by dividing the standardized incidence ratio of SPM in individuals with thyroid cancer treated with RAI compared to those not treated with RAI (with associated 95% confidence intervals [CI]). The natural logarithms of RRs of respective SPMs, weighted by the inverse of the variance, were pooled using fixed effects models and the exponential of the results was reported.

RESULTS

Two multi-center studies (one from Europe and the other from North America) were included in this review. The RR of SPMs in thyroid cancer survivors treated with RAI was significantly increased at 1.19 (95% confidence interval [CI] 1.04, 1.36, p = 0.010), relative to thyroid cancer survivors not treated with RAI (data from 16,502 individuals), using a minimum latency period of 2 to 3 years after thyroid cancer diagnosis. The RR of leukemia was also significantly increased in thyroid cancer survivors treated with RAI, with an RR of 2.5 (95% CI 1.13, 5.53, p = 0.024). We did not observe a significantly increased risk of the following cancers related to prior RAI treatment: bladder, breast, central nervous system, colon and rectum, digestive tract, stomach, pancreas, kidney (and renal pelvis), lung, or melanoma of skin.

CONCLUSIONS

The risk of SPMs in thyroid cancer survivors treated with RAI is slightly increased compared to thyroid cancer survivors not treated with RAI.

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.

Childhood thyroid cancers and radioactive iodine therapy: necessity of precautious radiation health risk management

One of the lessons from Chernobyl's legacy on health impact beyond 20 years is not only how to detect and treat the patients with radiation-associated thyroid cancers but how to follow up those who received radioactive iodine treatment repetitively after surgery in order to monitor any recurrence/worsening and also how to predict the risk of secondary primary cancers for their lifetime period. To evaluate the possibility of second primary tumors after radioactive iodine treatment, we reviewed the reports on risks from both external and internal radiation exposure, especially at high doses during childhood through an internet service of the National Library of Medicine and the National Institutes of Health, PubMed by the end of June, 2007, together with our own experience of Chernobyl childhood thyroid cancers. Children who were internally exposed after Chernobyl accident have a long-term risk of well differentiated thyroid cancers. Once they have disease, ironically radioactive iodine ablation is one of the useful therapies after surgical treatment. Elevated risks of solid cancers and leukemia have been found in radioiodine-treated patients, however, so far precious few reports from Chernobyl thyroid cancer patient were published. To reduce the adverse effects of radioactive iodine therapy on non-target tissues, recombinant human TSH has been applied and proved effective. Period of latency of second primary cancers may be very long. Therefore patients treated with high activities of radioactive iodine, especially children cases, should be carefully followed up during their whole lifespan.

Second primary malignancy risk in thyroid cancer survivors: a systematic review and meta-analysis

OBJECTIVE

To determine the risk of second primary malignancies (SPMs) in thyroid cancer survivors.

DESIGN

We performed a systematic review and meta-analysis examining the standardized incidence ratios (SIRs) of SPMs in thyroid cancer survivors (compared to individuals without thyroid cancer). Two independent reviewers screened citations and reviewed all full-text papers deemed potentially relevant. Final consensus was reached on inclusion of papers in the review. Data were pooled using fixed effects models.

MAIN OUTCOMES

Thirteen full-text papers were included. The incidence of SPMs in thyroid cancer survivors was increased with an SIR of 1.20 (95% confidence interval 1.17, 1.24) (based on pooled data from six studies of 70,844 thyroid cancer survivors). The SIR of the following SPMs was significantly increased: salivary gland, stomach, colon/colorectal, breast, prostate, kidney, brain/central nervous system, soft tissue sarcoma, non-Hodgkin's lymphoma, multiple myeloma, leukemia, bone/joints, and adrenal. A significantly reduced risk of lung and cervical cancers was observed.

CONCLUSIONS

Thyroid cancer survivors are at increased risk of SPMs, which may be related to disease-specific treatments or genetic predisposition.