Risk of solid subsequent malignant neoplasms after childhood Hodgkin lymphoma-Identification of high-risk populations to guide surveillance: A report from the Late Effects Study Group.

BACKGROUND: Survivors of Hodgkin lymphoma (HL) in childhood have an increased risk of subsequent malignant neoplasms (SMNs). Herein, the authors extended the follow-up of a previously reported Late Effects Study Group cohort and identified patients at highest risk for SMNs to create evidence for risk-based screening recommendations. METHODS: The standardized incidence ratio was calculated using rates from the Surveillance, Epidemiology, and End Results program as a reference. The risk of SMN was estimated using proportional subdistribution hazards regression. The cohort included 1136 patients who were diagnosed with HL before age 17 years between 1955 and 1986. The median length of follow-up was 26.6 years. RESULTS: In 162 patients, a total of 196 solid SMNs (sSMNs) were identified. Compared with the general population, the cohort was found to be at a 14-fold increased risk of developing an sSMN (95% confidence interval, 12.0-fold to 16.3-fold). The cumulative incidence of any sSMN was 26.4% at 40 years after a diagnosis of HL. Risk factors for breast cancer among females were an HL diagnosis between ages 10 years and 16 years and receipt of chest radiotherapy. Males treated with chest radiotherapy at age <10 years were found to be at highest risk of developing lung cancer. Survivors of HL who were treated with abdominal/pelvic radiotherapy and high-dose alkylating agents were found to be at highest risk of developing colorectal cancer and females exposed to neck radiotherapy at age <10 years were at highest risk of thyroid cancer. By age 50 years, the cumulative incidence of breast, lung, colorectal, and thyroid cancer was 45.3%, 4.2%, 9.5%, and 17.3%, respectively, among those at highest risk. CONCLUSIONS: Survivors of childhood HL remain at an increased risk of developing sSMNs. In the current study, subgroups of survivors of HL at highest risk of specific sSMNs were identified, and evidence for screening provided.

Systemic neoadjuvant chemotherapy for Group B intraocular retinoblastoma (ARET0331): A report from the Children's Oncology Group.

PURPOSE: To evaluate a chemoreduction regimen using systemic vincristine and carboplatin (VC) and local ophthalmic therapies to avoid external-beam radiotherapy (EBRT) or enucleation in patients with Group B intraocular retinoblastoma. PATIENTS AND METHODS: Twenty-one patients (25 eyes) were treated with six cycles of VC, accompanied by local ophthalmic therapies after cycle 1. The primary study objective was to determine the 2-year event-free survival (EFS) where an event was defined as the use of systemic chemotherapy in addition to vincristine or carboplatin, EBRT, and/or enucleation. RESULTS: All patients had tumor regression after the first cycle of VC and only two patients had progression during therapy. There were seven treatment failures within 2 years of study enrollment, resulting in 2-year EFS of 65% and early study closure in accordance with the statistical design. The 2-year cumulative incidence of enucleation was 15%; for external beam radiation therapy, it was 10%; and for chemotherapy to control progressive disease, it was 10%. All patients sustaining a treatment failure were salvaged with additional therapy. CONCLUSIONS: For the majority of patients with Group B intraocular retinoblastoma, chemoreduction with VC, without etoposide, in conjunction with local therapy provides excellent opportunity for ocular salvage. Local therapy given with every chemotherapy cycle and incorporation of etoposide may provide improved ocular salvage rates. Central review of group at diagnosis is critical in assigning appropriate therapies.

Adult cancer survivorship: evolution, research, and planning care.

Increases in the number of adult cancer survivors and other issues have forced the oncology community to examine, evaluate, and alter the cancer care paradigm. Pediatric oncologists are grappling with the task of transitioning a growing population of adult survivors of childhood cancer to adult medicine, while oncologists caring for adult cancer survivors are seeking models of follow-up care that are acceptable to patients and providers. Workforce and access-to-care issues suggest that primary care providers will see more cancer survivors in their practices across time, although it is unclear how prepared they are for this task. Translational research is needed to develop evidence-based clinical care and survivorship care plans. A broad picture of the evolving field of adult cancer survivorship is presented. The recent focus on young adult survivors of childhood cancer, an overview of translational research needed to inform the physical and psychosocial care of cancer survivors, and the roles of primary and specialty care providers managing this population is examined. Finally, an overview of evolving treatment summary and care plan initiatives is presented.

Parental nutrient intake and risk of retinoblastoma resulting from new germline RB1 mutation.

PURPOSE: We conducted a case-control study to examine the role of parents' nutrient intake before their child's conception in the child's risk of sporadic bilateral retinoblastoma, which results from a new germline RB1 mutation. METHODS: Parents of 206 cases from 9 North American institutions and 269 friend and relative controls participated; fathers of 182 cases and 223 controls and mothers of 202 cases and 260 controls provided useable information in telephone interviews on their diet in the year before the child's conception. We also asked parents about supplements, a significant source of nutrients in users. RESULTS: Father's intake of dairy-associated nutrients and his use of calcium supplements were associated with decreased risk, while his intake of copper, manganese, and vitamin E was associated with increased risk. Mother's use of multivitamins close to conception was associated with lower risk as was her intake of several micronutrients found in these supplements. In analyses to elucidate the primary factor from multiple correlated factors, the most robust findings were for father's calcium intake (adjusted OR = 0.46-0.63 for 700 mg increase) and calcium supplement use (OR = 0.35-0.41) and mother's multivitamin use (ORs 0.28-0.48). CONCLUSIONS: There are few directly relevant studies but some data indirectly support the biologic plausibility of the inverse associations with father's calcium intake and mother's use of multivitamins; however, we cannot rule out contributions of bias, confounding, or chance. Our findings provide a starting point for further investigation of diet in the etiology of retinoblastoma and new germline mutation generally.

Relevance of historical therapeutic approaches to the contemporary treatment of pediatric solid tumors.

Children with solid tumors, most of which are malignant, have an excellent prognosis when treated on contemporary regimens. These regimens, which incorporate chemotherapeutic agents and treatment modalities used for many decades, have evolved to improve relapse-free survival and reduce long-term toxicity. This review discusses the evolution of the treatment regimens employed for management of the most common solid tumors, emphasizing the similarities between contemporary and historical regimens. These similarities allow the use of historical patient cohorts to identify the late effects of successful therapy and to evaluate remedial interventions for these adverse effects.

A mouse model for studying therapy-induced cancers.

As more pediatric cancer patients survive for longer periods following treatment with cytotoxic agents, therapy-induced second malignant neoplasms (SMNs) have become a major concern. In this issue of Cancer Cell, Chao et al. report that mice carrying a mutation in Nf1, the gene responsible for neurofibromatosis type 1, treated with radiation and/or cyclophosphamide, developed tumors similar to human SMNs at a significantly higher rate than did wild-type controls treated similarly. This model provides efficient and rational means for testing procedures and agents that could inform clinicians regarding second cancer risks associated with treatment and, perhaps, reducing them.

Second malignant neoplasms following chemoreduction with carboplatin, etoposide, and vincristine in 245 patients with intraocular retinoblastoma.

BACKGROUND: To evaluate the occurrence of second malignant neoplasms (SMN) following chemoreduction (CRD) with carboplatin, vincristine, and etoposide (CEV) as frontline therapy in patients with retinoblastoma (RB). PRODECURE: We conducted a two-institution retrospective chart review of 245 patients with intraocular RB treated with six cycles of vincristine, carboplatin, and etoposide for treatment of intraocular retinoblastoma. Cumulative incidence of SMN was calculated with adjustment for the competing risk of death. RESULTS: There were 187 patients with germline retinoblastoma and 58 with non-germline disease. External beam radiotherapy was subsequently utilized in 46 (24%) of germline cases and six (10%) of non-germline cases. Mean follow-up of germline and non-germline patients was 80 and 70 months, respectively. Seven subsequent cancers were found in six patients for an overall incidence of 3% at a mean of 11 years. For germline cases, following CEV alone (n = 156), SMN were found in 4% following the RB diagnosis. We found no SMN in patients with non-germline RB. One patient developed pineoblastoma. SMN included osteosarcoma (n = 3), rhabdomyosarcoma (n = 1), orbital and conjunctival melanoma (n = 1), low-grade glioma (n = 1), and acute promyeloctic leukemia (n = 1). Five of the six patients with a second malignancy survive at mean of 46 months (range 15-71 months). CONCLUSIONS: At a mean of 11 years, 4% of children with germline RB treated with CEV as frontline therapy developed SMN's. No SMN was found in non-germline patients. Concerns regarding CEV-induced second cancers should not deter clinicians from using life and vision preserving therapy in patients with retinoblastoma.

A revision of the intensity of treatment rating scale: classifying the intensity of pediatric cancer treatment.

BACKGROUND: We previously developed a reliable and valid method for classifying the intensity of pediatric cancer treatment. The Intensity of Treatment Rating Scale (ITR-2.0) 1 classifies treatments into four operationally defined levels of intensity and is completed by pediatric oncology specialists based on diagnosis, stage, and treatment data from the medical record. Experience with the ITR-2.0 and recent changes in treatment protocols indicated the need for a minor revision and revalidation. METHODS: Five criterion raters reviewed the prior items, independently proposing additions and/or changes in the classification of diseases/treatments. Subsequent to a group discussion of the proposed changes, a revised 43-item ITR was evaluated. Pediatric oncologists (n = 47) completed a two-part online questionnaire. Validity of the classifications was determined by the oncologists classifying each disease/treatment into one of the four levels of intensity. Inter-rater reliability was calculated by having each oncologist classify the treatments of 12 sample patients using the new version which we call the ITR-3. RESULTS: Agreement between median ratings of the 43 items for the pediatric oncologists and the criterion raters was high (r = 0.88). The median of the raters was either identical (81%) with the criterion ratings or discrepant by one level. Inter-rater reliability was very high when using the ITR-3 to classify 12 sample patients, with a median agreement of 0.90 and an intraclass correlation coefficient (r(ICC) = 0.86). CONCLUSIONS: With these minor modifications and updates, the ITR-3 remains a reliable and valid method for classifying pediatric oncology treatment protocols.

Medical radiation exposure and risk of retinoblastoma resulting from new germline RB1 mutation.

Although ionizing radiation induces germline mutations in animals, human studies of radiation-exposed populations have not detected an effect. We conducted a case-control study of sporadic bilateral retinoblastoma, which results from a new germline RB1 mutation, to investigate gonadal radiation exposure of parents from medical sources before their child's conception. Parents of 206 cases from nine North American institutions and 269 controls participated; fathers of 184 cases and 223 friend and relative controls and mothers of 204 cases and 260 controls provided information in telephone interviews on their medical radiation exposure. Cases provided DNA for RB1 mutation testing. Of common procedures, lower gastrointestinal (GI) series conferred the highest estimated dose to testes and ovaries. Paternal history of lower GI series was associated with increased risk of retinoblastoma in the child [matched odds ratio (OR) = 3.6, 95% confidence interval (CI) = 1.2-11.2, two-sided p = 0.02], as was estimated total testicular dose from all procedures combined (OR for highest dose=3.9, 95% CI = 1.2-14.4, p = 0.02). Maternal history of lower GI series was also associated with increased risk (OR = 7.6, 95% CI = 2.8-20.7, p < 0.001) as was the estimated total dose (OR for highest dose = 3.0, 95% CI = 1.4-7.0, p = 0.005). The RB1 mutation spectrum in cases of exposed parents did not differ from that of other cases. Some animal and human data support our findings of an association of gonadal radiation exposure in men and women with new germline RB1 mutation detectable in their children, although bias, confounding, and/or chance may also explain the results.

Systematic review: surveillance for breast cancer in women treated with chest radiation for childhood, adolescent, or young adult cancer.

BACKGROUND: Women treated with therapeutic chest radiation may develop breast cancer. PURPOSE: To summarize breast cancer risk and breast cancer surveillance in women after chest radiation for pediatric or young adult cancer. DATA SOURCES: Studies from MEDLINE, EMBASE, the Cochrane Library, and CINAHL (1966 to December 2008). STUDY SELECTION: Articles were selected to answer any of 3 questions: What is the incidence and excess risk for breast cancer in women after chest radiation for pediatric or young adult cancer? For these women, are the clinical characteristics of breast cancer and the outcomes after therapy different from those of women with sporadic breast cancer in the general population? What are the potential benefits and harms associated with breast cancer surveillance among women exposed to chest radiation? DATA EXTRACTION: Three investigators independently extracted data and assessed study quality. DATA SYNTHESIS: Standardized incidence ratios ranged from 13.3 to 55.5; cumulative incidence of breast cancer by age 40 to 45 years ranged from 13% to 20%. Risk for breast cancer increased linearly with chest radiation dose. Available limited evidence suggests that the characteristics of breast cancer in these women and the outcomes after diagnosis are similar to those of women in the general population; mammography can detect breast cancer, although sensitivity is limited. LIMITATION: The quality of evidence for key questions 2 and 3 is limited by substantial study heterogeneity, variation in study design, and small sample size. CONCLUSION: Women treated with chest radiation have a substantially elevated risk for breast cancer at a young age, which does not seem to plateau. In this high-risk population, there seems to be a benefit associated with early detection. Further research is required to better define the harms and benefits of lifelong surveillance.

Chronic health conditions in adult survivors of childhood cancer.

BACKGROUND: Only a few small studies have assessed the long-term morbidity that follows the treatment of childhood cancer. We determined the incidence and severity of chronic health conditions in adult survivors. METHODS: The Childhood Cancer Survivor Study is a retrospective cohort study that tracks the health status of adults who received a diagnosis of childhood cancer between 1970 and 1986 and compares the results with those of siblings. We calculated the frequencies of chronic conditions in 10,397 survivors and 3034 siblings. A severity score (grades 1 through 4, ranging from mild to life-threatening or disabling) was assigned to each condition. Cox proportional-hazards models were used to estimate hazard ratios, reported as relative risks and 95% confidence intervals (CIs), for a chronic condition. RESULTS: Survivors and siblings had mean ages of 26.6 years (range, 18.0 to 48.0) and 29.2 years (range, 18.0 to 56.0), respectively, at the time of the study. Among 10,397 survivors, 62.3% had at least one chronic condition; 27.5% had a severe or life-threatening condition (grade 3 or 4). The adjusted relative risk of a chronic condition in a survivor, as compared with siblings, was 3.3 (95% CI, 3.0 to 3.5); for a severe or life-threatening condition, the risk was 8.2 (95% CI, 6.9 to 9.7). Among survivors, the cumulative incidence of a chronic health condition reached 73.4% (95% CI, 69.0 to 77.9) 30 years after the cancer diagnosis, with a cumulative incidence of 42.4% (95% CI, 33.7 to 51.2) for severe, disabling, or life-threatening conditions or death due to a chronic condition. CONCLUSIONS: Survivors of childhood cancer have a high rate of illness owing to chronic health conditions.

Chemoreduction for group E retinoblastoma: comparison of chemoreduction alone versus chemoreduction plus low-dose external radiotherapy in 76 eyes.

PURPOSE: To evaluate chemoreduction (CRD) for group E retinoblastoma. DESIGN: Retrospective, comparative case series. PARTICIPANTS: Seventy-six eyes of 56 patients with group E retinoblastoma were treated with CRD alone or CRD plus low-dose prophylactic external beam radiotherapy (CRD+P-EBR). The CRD included vincristine, etoposide, and carboplatin (6 cycles). The P-EBR was given routinely 2 months after completion of CRD at a suggested dose of 2600 cGy. Therapeutic EBR (T-EBR) was only given at the time of extensive tumor recurrence at a suggested dose of 3800 cGy. METHODS: Retrospective chart review. MAIN OUTCOME MEASURES: Globe salvage. RESULTS: Of the 76 eyes, 64 received CRD alone and 12 received CRD+P-EBR. At the 2-year follow-up, globe salvage was achieved in 29 (53%) of 55 eyes in the CRD group and in 10 (91%) of 11 eyes in the CRD+P-EBR group. At 5 years, globe salvage was achieved in 20 (48%) of 42 eyes in the CRD group and in 4 (80%) of 5 eyes in the CRD+P-EBR group (P=0.347). Of the 64 eyes in the CRD group, 16 (25%) were salvaged with CRD alone and 13 (20%) with CRD+T-EBR, whereas 22 (34%) were enucleated after CRD alone and 13 (20%) were enucleated after CRD+T-EBR. Of the 12 eyes in the CRD+P-EBR group, 10 (83%) were salvaged with CRD+P-EBR, whereas 2 (17%) were enucleated and none required T-EBR. The median dose for T-EBR was 3800 cGy, and that for P-EBR was 2600 cGy. Eyes treated with CRD+P-EBR showed significantly less recurrence, leading to less chance of enucleation or therapeutic radiotherapy than that for CRD alone (P<0.001). Visual acuity was 20/100 or better or fix and follow in 9 (32%) of 28 salvaged eyes in the CRD group and in 4 (40%) of 10 in the CRD+P-EBR group. At 5 years, there were no patients in either group with metastasis of pinealoblastoma or who had died. In one patient in the CRD group, a second cancer developed. CONCLUSIONS: Group E retinoblastoma managed with CRD+P-EBR showed significantly less need for enucleation or therapeutic radiotherapy than eyes treated with CRD alone. These findings merit further study and consideration.

A retrospective review of hearing in children with retinoblastoma treated with carboplatin-based chemotherapy.

BACKGROUND: Retinoblastoma occurs in approximately 4 per million children per year in the United States, usually before 2 years of age. In developed countries, 95% of children with tumor in one eye can be cured with enucleation, while children with tumor in both eyes require individualized therapy to preserve vision. Although enucleation and radiation are very effective therapies for children with bilateral disease, the resultant visual impairment, cosmetic deformity and risk for new tumors result in morbidity to these children who otherwise have a near normal lifespan. Therefore, since 1994, chemoreduction with vincristine, carboplatin, and etoposide combined with focal treatment, have been used successfully. However, a major concern with the use of carboplatin has been ototoxicity. PROCEDURES: To determine whether carboplatin, in the doses and schedule used by us and others to treat retinoblastoma (18.6 mg/kg q 4 weeks for six cycles) results in hearing impairment, we reviewed the records of 248 children with retinoblastoma, 164 of whom had received carboplatin. Children generally received carboplatin, vincristine, and etoposide (CEV) for six cycles of chemotherapy. RESULTS: Hearing evaluations prior to initiating therapy were abnormal in 14 patients (5.6%). No patients with normal initial audiograms were found to have abnormal studies following repeated evaluations. CONCLUSION: While ototoxicity is a potential concern in this young patient population, carboplatin in the treatment of retinoblastoma does not appear to produce impairment. Screening can identify children who require frequent audiologic follow-up, but children whose hearing is normal prior to therapy do not require routine surveillance following six cycles of standard CEV therapy.

Sperm banking for adolescent and young adult cancer patients: sperm quality, patient, and parent perspectives.

BACKGROUND: Infertility is often a complication for adolescent and young adult males who receive cancer therapy, a problem that might be averted through using cryopreserved sperm. We aim to evaluate feasibility of offering newly diagnosed patients the opportunity to bank sperm and, to determine the beliefs and decision-making processes of patients and their parents who considered sperm banking. PROCEDURE: Eligible patients and parents were approached and offered sperm cryopreservation. Semen samples from patients who sequentially attempted sperm banking were analyzed. Questionnaires were then administered to patients and parents who had been approached about sperm banking. RESULTS: Semen samples from 68 patients were analyzed. Nine patients were azoospermic; all had been pre-treated with chemotherapy. Fifty patients completed the questionnaire. Parent and patient made the decision together to bank 80% of the time. All sons who attempted to bank and their parents felt they had made the right decision, including those who attempted but failed. CONCLUSIONS: Viable sperm can be collected successfully from adolescent and young adults who are newly diagnosed with cancer. Semen quality was dramatically reduced by one course of gonadotoxic therapy. Parents and patients want information regarding sperm cryopreservation early. Parents appear to play an important role in the decision to sperm bank. We recommend sperm banking be offered to all eligible patients.

Nonmelanoma skin cancer in survivors of childhood and adolescent cancer: a report from the childhood cancer survivor study.

PURPOSE: Nonmelanoma skin cancer (NMSC) has become the most common type of cancer in many populations throughout the world. Ultraviolet and ionizing radiation are known risk factors. Because NMSCs are rarely lethal and most cancer registries do not routinely report data regarding these cancers, they have received little attention in studies evaluating long-term effects of cancer therapy. This article reports on the occurrence of secondary NMSC as a long-term effect of cancer therapy in survivors of childhood cancer. PATIENTS AND METHODS: The Childhood Cancer Survivor Study (CCSS) is a cohort study of 5-year survivors of childhood and adolescent cancer from 25 participating institutions in North America. NMSC patients were defined by a history of basal cell or squamous cell carcinoma of the skin after primary malignancy treatment. Demographic and treatment data were collected and analyzed. RESULTS: Among the 13,132 eligible CCSS participants, 213 have reported NMSC; 99 patients (46%) have had multiple occurrences. Median age of occurrence was 31 years (range, 7 to 46 years). Location of NMSC included head and neck (43%), back (24%), chest (22%), abdomen and pelvis (5%), extremity (3%), and unknown (4%). Ninety percent of patients had previously received radiation therapy (RT); 90% of tumors occurred within the RT field. RT was associated with a 6.3-fold increase in risk (95% CI, 3.5- to 11.3-fold). CONCLUSION: Long-term survivors of childhood and adolescent cancer who were treated with RT are at highest risk for developing NMSC. Educational efforts need to be directed to this population to facilitate early diagnosis of NMSC and reduction in sun exposure.

Primary thyroid cancer after a first tumour in childhood (the Childhood Cancer Survivor Study): a nested case-control study.

BACKGROUND: Survivors of malignant disease in childhood who have had radiotherapy to the head, neck, or upper thorax have an increased risk of subsequent primary thyroid cancer, but the magnitude of risk over the therapeutic dose range has not been well established. We aimed to quantify the long-term risk of thyroid cancer after radiotherapy and chemotherapy. METHODS: In a nested case-control study, 69 cases with pathologically confirmed thyroid cancer and 265 matched controls without thyroid cancer were identified from 14,054 5-year survivors of cancer during childhood from the Childhood Cancer Survivor Study cohort. Childhood cancers were diagnosed between 1970 and 1986 with cohort follow-up to 2000. FINDINGS: Risk of thyroid cancer increased with radiation doses up to 20-29 Gy (odds ratio 9.8 [95% CI 3.2-34.8]). At doses greater than 30 Gy, a fall in the dose-response relation was seen. Both the increased and decreased risks were more pronounced in those diagnosed with a first primary malignant disease before age 10 years than in those older than 10 years. Furthermore, the fall in risk remained when those diagnosed with Hodgkin's lymphoma were excluded. Chemotherapy for the first cancer was not associated with thyroid-cancer risk, and it did not modify the effect of radiotherapy. 29 (42%) cases had a first diagnosis of Hodgkin's lymphoma compared with 49 (19%) controls. 11 (42%) of those who had Hodgkin's lymphoma had subsequent thyroid cancers smaller than 1 cm compared with six (17%) of those who had other types of childhood cancer (p=0.07). INTERPRETATION: The reduction in radiation dose-response for risk of thyroid cancer after childhood exposure to thyroid doses higher than 30 Gy is consistent with a cell-killing effect. Standard long-term follow-up of patients who have had Hodgkin's lymphoma for detection of thyroid cancer should also be undertaken for survivors of any cancer during childhood who received radiotherapy to the thorax or head and neck region.

The International Classification of Retinoblastoma predicts chemoreduction success.

PURPOSE: To evaluate the reliability of the International Classification of Retinoblastoma (ICRB) for predicting treatment success with chemoreduction (CRD). DESIGN: Noncomparative interventional case series. PARTICIPANTS: Two hundred forty-nine consecutive eyes. METHODS: All eyes were treated with CRD and were classified according to the ICRB: group A included those eyes with retinoblastoma 3 mm, macular location, or minor subretinal fluid; group C included those eyes with retinoblastoma with localized seeds; group D included those eyes with retinoblastoma with diffuse seeds; group E included those eyes with massive retinoblastoma necessitating enucleation. The CRD regimen included vincristine, etoposide, and carboplatin for 6 cycles plus local consolidation with thermotherapy or cryotherapy. MAIN OUTCOME MEASURE: Chemoreduction success, defined as avoidance of external beam radiotherapy or enucleation. RESULTS: Of the 249 eyes, 23 (9%) were in group A, 96 (39%) were in group B, 21 (8%) were in group C, and 109 (44%) were in group D. In this series, group E eyes were managed with enucleation. Treatment success was achieved in 100% of group A, 93% of group B, 90% of group C, and 47% of group D eyes. CONCLUSIONS: The ICRB can be of assistance in predicting CRD success for retinoblastoma. Additional treatment methods are necessary to salvage more group D eyes.

Thyroid cancer in childhood cancer survivors: a detailed evaluation of radiation dose response and its modifiers.

Radiation exposure at a young age is a strong risk factor for thyroid cancer. We conducted a nested case-control study of 69 thyroid cancer cases and 265 controls from a cohort of 14,054 childhood cancer survivors to evaluate the shape of the radiation dose-response relationship, in particular at high doses, and to assess modification of the radiation effects by patient and treatment characteristics. We considered several types of statistical models to estimate the excess relative risk (ERR), mainly guided by radiobiological models. A two-parameter model with a term linear in dose and a negative exponential in dose squared provided the best parsimonious description with an ERR of 1.3 per gray (95% confidence interval 0.4-4.1) at doses below 6 Gy and a relative decrease in ERR of 0.2% per unit dose squared with increasing dose, that is, decreases in the ERR/Gy of 53% at 20 Gy and 95% at 40 Gy. Further analyses using spline models suggested that the significant nonlinearity at high doses was characterized most appropriately as a true downturn rather than a flattening of the dose-response curve. We found no statistically significant modification of the dose-response relationship by patient characteristics; however, the linear parameter (i.e., the ERR/ Gy at doses less than 6 Gy) did decrease consistently and linearly with increasing age at childhood cancer diagnosis, from 4.45 for 0-1-year-olds to 0.48 for 15-20-year-olds. In summary, we applied models derived from radiobiology to describe the radiation dose-response curve for thyroid cancer in an epidemiological study and found convincing evidence for a downturn in risk at high doses.