Genetically mediated Nf1 loss in mice promotes diverse radiation-induced tumors modeling second malignant neoplasms

Salivary Duct Carcinoma Arising in the Submandibular Gland in a Patient with Neurofibromatosis Type 1

A 71-year-old man with neurofibromatosis type 1 (NF1) presented to our department with a 1-week history of a painful mass in the left submandibular area. Computed tomography (CT) and magnetic resonance imaging revealed an irregular-shaped tumor with a diameter of 2.0 cm in the left submandibular gland and a metastatic lymph node with a diameter of 1.0 cm adjacent to the tumor. Fluorodeoxyglucose-positron emission tomography/CT revealed increased uptake in the tumor. Fine-needle aspiration cytology revealed atypical cells, suggesting salivary duct carcinoma (SDC). Left neck dissection with resection of the tumor and submandibular gland was performed under general anesthesia. Histologic examination revealed ductal formation with a solid, cystic, cribriform, and papillary structure with intraductal comedonecrosis, diagnosing as SDC originating in the submandibular gland (pT3N1M0 pStage III). Mutational analysis of 160 cancer-related genes by next-generation sequencing (NGS) revealed a germline and frameshift mutation in the NF1 gene (p.R2408Kfs*14) and a somatic and frameshift mutation in the TP53 gene (p.C176Wfs*22). The patient received postoperative radiotherapy to the left neck area at 66 Gy. No evidence of recurrence or metastasis has been observed as of 10 months postoperatively. This is the first reported case of SDC in the submandibular gland in a patient with NF1. The mutational data by NGS may contribute to a better understanding of the oncogenesis of SDC in patients with NF1.

Considerations for carcinogenesis countermeasure development using mouse models

Activities in space will expose humans to profoundly new environments, challenging human performance and will require innovative supportive technologies. Among these environmental variables, exposure to ionizing radiation is a major concern for astronauts, as the long-term effects of exposure on diverse tissues are poorly understood. This need however creates opportunities for novel approaches, particularly in the development of countermeasures against the effects of ionizing radiation exposure. Carcinogenesis presents a unique challenge as a disease process, due to the inherent complexities of the process and the challenges of obtaining a large volume of clinical evidence. Thus, developing the countermeasures to address potential effects of ionizing radiation exposure will require understanding biological underpinnings to design countermeasures effectively in conjunction with highly robust modeling approaches to test and examine in vivo. This review will highlight specific considerations for accelerated development of space radiation countermeasures against carcinogenesis.

Irradiation of Nf1 mutant mouse models of spinal plexiform neurofibromas drives pathologic progression and decreases survival

Background

Genetically susceptible individuals can develop malignancies after irradiation of normal tissues. In the context of therapeutic irradiation, it is not known whether irradiating benign neoplasms in susceptible individuals promotes neoplastic transformation and worse clinical outcomes. Individuals with Neurofibromatosis 1 (NF1) are susceptible to both radiation-induced second malignancies and spontaneous progression of plexiform neurofibromas (PNs) to malignant peripheral nerve sheath tumors (MPNSTs). The role of radiotherapy in the treatment of benign neoplasms such as PNs is unclear.

Methods

To test whether radiotherapy promotes neoplastic progression of PNs and reduces overall survival, we administered spinal irradiation (SI) to conditional knockout mouse models of NF1-associated PNs in 2 germline contexts: Nf1^fllfl; PostnCre⁺ and Nf1^fl/-; PostnCre⁺. Both genotypes develop extensive Nf1 null spinal PNs, modeling PNs in NF1 patients. A total of 101 mice were randomized to 0 Gy, 15 Gy (3 Gy × 5), or 30 Gy (3 Gy × 10) of spine-focused, fractionated SI and aged until signs of illness.

Results

SI decreased survival in both Nf1^fllfl mice and Nf1^fl/- mice, with the worst overall survival occurring in Nf1^fl/- mice receiving 30 Gy. SI was also associated with increasing worrisome histologic features along the PN-MPNST continuum in PNs irradiated to higher radiation doses.

Conclusions

This preclinical study provides experimental evidence that irradiation of pre-existing PNs reduces survival and may shift PNs to higher grade neoplasms.

Current overview and special considerations for second breast cancer in Hodgkin lymphoma survivors

Second breast cancer (SBC) is the most common solid cancer among Hodgkin Lymphoma (HL) female survivors. We reviewed the related modifying risk factors, radiation-induced carcinogenesis, tumors characteristics, management specificities, prevention and surveillance modalities based on current evidence. The risk of developing SBC may be influenced essentially by the age at HL treatment, follow-up latency, dose of irradiation received and the extent of irradiated field. SBCs generally develop at younger age, they are often bilateral, and exhibit more aggressive biological features and worse prognosis. No firm answer about the benefits of breast surveillance is provided by literature, but compelling evidence tends toward a clinical benefit in early detection. Increasing awareness among health providers' care and current survivors as well as the implementation of screening measures is crucial. Great efforts are ongoing in individualizing treatment strategies for future HL patients and response-adapted approaches are holding promise in prevention of these second malignancies.

Advancement in research and therapy of NF1 mutant malignant tumors

The NF1 gene encodes neurofibromin, which is one of the primary negative regulatory factors of the Ras protein. Neurofibromin stimulates the GTPase activity of Ras to convert it from an active GTP-bound form to its inactive GDP-bound form through its GTPase activating protein-related domain (GRD). Therefore, neurofibromin serves as a shutdown signal for all vertebrate RAS GTPases. NF1 mutations cause a resultant decrease in neurofibromin expression, which has been detected in many human malignancies, including NSCLC, breast cancer and so on. NF1 mutations are associated with the underlying mechanisms of treatment resistance discovered in multiple malignancies. This paper reviews the possible mechanisms of NF1 mutation-induced therapeutic resistance to chemotherapy, endocrine therapy and targeted therapy in malignancies. Then, we further discuss advancements in targeted therapy for NF1-mutated malignant tumors. In addition, therapies targeting the downstream molecules of NF1 might be potential novel strategies for the treatment of advanced malignancies.

Nf1-Mutant Tumors Undergo Transcriptome and Kinome Remodeling after Inhibition of either mTOR or MEK

Loss of the tumor suppressor NF1 leads to activation of RAS effector pathways, which are therapeutically targeted by inhibition of mTOR (mTORi) or MEK (MEKi). However, therapeutic inhibition of RAS effectors leads to the development of drug resistance and ultimately disease progression. To investigate molecular signatures in the context of NF1 loss and subsequent acquired drug resistance, we analyzed the exomes, transcriptomes, and kinomes of Nf1-mutant mouse tumor cell lines and derivatives of these lines that acquired resistance to either MEKi or mTORi. Biochemical comparisons of this unique panel of tumor cells, all of which arose in Nf1^+/- mice, indicate that loss of heterozygosity of Nf1 as an initial genetic event does not confer a common biochemical signature or response to kinase inhibition. Although acquired drug resistance by Nf1-mutant tumor cells was accompanied by altered kinomes and irreversibly altered transcriptomes, functionally in multiple Nf1-mutant tumor cell lines, MEKi resistance was a stable phenotype, in contrast to mTORi resistance, which was reversible. Collectively, these findings demonstrate that Nf1-mutant tumors represent a heterogeneous group biochemically and undergo broader remodeling of kinome activity and gene expression in response to targeted kinase inhibition.

Overcoming BET Inhibitor Resistance in Malignant Peripheral Nerve Sheath Tumors

PURPOSE

BET bromodomain inhibitors have emerged as a promising therapy for numerous cancer types in preclinical studies, including neurofibromatosis type 1 (NF1)-associated malignant peripheral nerve sheath tumor (MPNST). However, potential mechanisms underlying resistance to these inhibitors in different cancers are not completely understood. In this study, we explore new strategy to overcome BET inhibitor resistance in MPNST.Experimental Design: Through modeling tumor evolution by studying genetic changes underlying the development of MPNST, a lethal sarcoma with no effective medical treatment, we identified a targetable addiction to BET bromodomain family member BRD4 in MPNST. This served as a controlled model system to delineate mechanisms of sensitivity and resistance to BET bromodomain inhibitors in this disease.

RESULTS

Here, we show that a malignant progression-associated increase in BRD4 protein levels corresponds to partial sensitivity to BET inhibition in MPNST. Strikingly, genetic depletion of BRD4 protein levels synergistically sensitized MPNST cells to diverse BET inhibitors in culture and in vivo.

CONCLUSIONS

Collectively, MPNST sensitivity to combination genetic and pharmacologic inhibition of BRD4 revealed the presence of a unique addiction to BRD4 in MPNST. Our discovery that a synthetic lethality exists between BET inhibition and reduced BRD4 protein levels nominates MPNST for the investigation of emerging therapeutic interventions such as proteolysis-targeting chimeras (PROTACs) that simultaneously target bromodomain activity and BET protein abundance.

Proton therapy for treatment of intracranial benign tumors in adults: A systematic review

INTRODUCTION

The depth-dose distribution of a proton beam, materialized by the Bragg peak makes it an attractive radiation modality as it reduces exposure of healthy tissues to radiations, compared with photon therapy Prominent indications, based on a long-standing experience are: intraocular melanomas, low-grade skull-base and spinal canal malignancies. However, many others potential indications are under investigations such as the benign morbid conditions that are compatible with an extended life-expectancy: low grade meningiomas, paragangliomas, pituitary adenomas, neurinomas craniopharyngioma or recurrent pleomorphic adenomas.

MATERIALS

Given the radiation-induced risk of secondary cancer and the potential neurocognitive and functional alteration with photonic radiotherapy, we systematically analyzed the existing clinical literature about the use of proton therapy as an irradiation modality for cervical or intracranial benign tumors. The aim of this review was to report clinical outcomes of adult patients with benign intracranial or cervical tumors treated with proton therapy and to discuss about potential advantages of proton therapy over intensity modulated radiotherapy or radiosurgery.

RESULTS

Twenty-four studies were included. There was no randomized studies. Most studies dealt with low grade meningiomas (n = 9). Studies concerning neurinoma (n = 4), pituitary adenoma (n = 5), paraganglioma (n = 5), or craniopharyngioma (n = 1) were fewer. Whatever the indication, long term local control was systematically higher than 90% and equivalent to series with conventional radiotherapy.

CONCLUSION

Proton-therapy for treatment of adult benign intracranial and cervical tumors is safe. Randomized or prospective cohorts with long term cognitive evaluations are needed to assess the real place of proton-therapy in the treatment of adults benign head and neck tumors.

Radiogenomic Predictors of Adverse Effects following Charged Particle Therapy

Radiogenomics is the study of genomic factors that are associated with response to radiation therapy. In recent years, progress has been made toward identifying genetic risk factors linked with late radiation-induced adverse effects. These advances have been underpinned by the establishment of an international Radiogenomics Consortium with collaborative studies that expand cohort sizes to increase statistical power and efforts to improve methodologic approaches for radiogenomic research. Published studies have predominantly reported the results of research involving patients treated with photons using external beam radiation therapy. These studies demonstrate our ability to pool international cohorts to identify common single nucleotide polymorphisms associated with risk for developing normal tissue toxicities. Progress has also been achieved toward the discovery of genetic variants associated with radiation therapy-related subsequent malignancies. With the increasing use of charged particle therapy (CPT), there is a need to establish cohorts for patients treated with these advanced technology forms of radiation therapy and to create biorepositories with linked clinical data. While some genetic variants are likely to impact toxicity and second malignancy risks for both photons and charged particles, it is plausible that others may be specific to the radiation modality due to differences in their biological effects, including the complexity of DNA damage produced. In recognition that the formation of patient cohorts treated with CPT for radiogenomic studies is a high priority, efforts are underway to establish collaborations involving institutions treating cancer patients with protons and/or carbon ions as well as consortia, including the Proton Collaborative Group, the Particle Therapy Cooperative Group, and the Pediatric Proton Consortium Registry. These important radiogenomic CPT initiatives need to be expanded internationally to build on experience gained from the Radiogenomics Consortium and epidemiologists investigating normal tissue toxicities and second cancer risk.

Review of risk factors of secondary cancers among cancer survivors

Improvements in cancer survival have made the long-term risks from treatments more important, in particular among the children, adolescents and young adults who are more at risk particularly due to a longer life expectancy and a higher sensitivity to treatments. Subsequent malignancies in cancer survivors now constitute 15 to 20% of all cancer diagnoses in the cancer registries. Lots of studies are published to determine risk factors, with some controversial findings. Just data from large cohorts with detailed information on individual treatments and verification of what is called "secondary cancers" can add some knowledge, because their main difficulty is that the number of events for most second cancer sites are low, which impact the statistical results. In this review of the literature, we distinguish second and secondary cancers and discuss the factors contributing to this increased risk of secondary cancers. The article concludes with a summary of current surveillance and screening recommendations.

Therapy-related myeloid neoplasms: when genetics and environment collide

Therapy-related myeloid neoplasms (t-MN) arise as a late effect of chemotherapy and/or radiation administered for a primary condition, typically a malignant disease, solid organ transplant or autoimmune disease. Survival is measured in months, not years, making t-MN one of the most aggressive and lethal cancers. In this Review, we discuss recent developments that reframe our understanding of the genetic and environmental aetiology of t-MN. Emerging data are illuminating who is at highest risk of developing t-MN, why t-MN are chemoresistant and how we may use this information to treat and ultimately prevent this lethal disease.

A pooled mutational analysis identifies ionizing radiation-associated mutational signatures conserved between mouse and human malignancies

Single nucleotide variants (SNVs) identified in cancer genomes can be de-convolved using non-negative matrix factorization (NMF) into discrete trinucleotide-based mutational signatures indicative of specific cancer-causing processes. The stability of NMF-generated mutational signatures depends upon the numbers of variants available for analysis. In this work, we sought to assess whether data from well-controlled mouse models can compensate for scarce human data for some cancer types. High quality sequencing data from radiotherapy-induced cancers is particularly scarce and the mutational processes defining ionizing radiation (IR)-induced mutagenesis in vivo are poorly defined. Here, we combine sequencing data from mouse models of IR-induced malignancies and human IR-induced malignancies. To determine whether the signatures identified from IR-exposed subjects can be differentiated from other mutagenic signatures, we included data from an ultraviolet radiation (UV)-induced human skin cancer and from a mouse model of urethane-induced cancers. NMF distinguished all three mutagens and in the pooled analysis IR was associated with mutational signatures common to both species. These findings illustrate the utility of pooled analysis of mouse and human sequencing data.

Histologically benign, clinically aggressive: Progressive non-optic pathway pilocytic astrocytomas in adults with NF1

Although optic pathway gliomas are the most common brain tumors associated with neurofibromatosis type 1 (NF1), extra-optic gliomas occur and may behave more aggressively with outcomes that differ by age. A retrospective case-control study was designed to describe the clinical course of adult NF1 patients with progressive extra-optic pilocytic astrocytomas (PAs) and compare to a pediatric cohort. Data for patients treated at the Johns Hopkins Comprehensive Neurofibromatosis Center from 2003 to 2013 were reviewed to identify cases (adults, age >18) and controls (pediatric, age <18) with clinically or radiographically progressive extra-optic PAs. Demographic, clinical, histologic, and radiographic data were collected. Three adult NF1 cases and four pediatric NF1 controls were identified. Mean age was 32.3 ± 9.5 years, 66% male (cases); 12.8 ± 4.2 years, 100% male (controls). Symptomatic progression occurred in two-of-three adults (67%) while the majority of pediatric patients presented with isolated radiographic progression (n = 3, 75%). Onset tended to be more rapid in adults (4 ± 1 vs. 14 ± 8.3 months, P = 0.10). Subtotal resection was the treatment for all pediatric patients. Radiotherapy (n = 2), chemotherapy (n = 2), and targeted, biologic agents (n = 2) were administered in adults. Although all pediatric patients are living, outcomes were universally poor in adults with progression to death in all (median survival 17.1 months, range 6.6-30.3). In conclusion, despite grade I histology, all three adult NF1 patients with progressive extra-optic PAs suffered an aggressive clinical course which was not seen in pediatric patients. Clinicians should be aware of this clinico-histologic discrepancy when counseling and managing adult NF1 patients with progressive extra-optic PAs. © 2016 Wiley Periodicals, Inc.

Secondary cancers after a childhood cancer diagnosis: a nationwide hospital-based retrospective cohort study in Japan

BACKGROUND

The epidemiology of secondary cancers in childhood cancer survivors has been unknown in Asian countries. Our aim is to assess the incidence and risk factors for secondary cancers through a nationwide survey in Japan.

METHODS

A retrospective cohort study comprising 10,069 children who were diagnosed with cancer between 1980 and 2009 was conducted in 15 Japanese hospitals. The cumulative incidence rate was calculated using death as the competing risk and compared by the Gray method. The standardized incidence ratio (SIR) was defined as the ratio of the number of observed cancers divided by the number of expected cancers. The risk factors were analyzed using Cox regression analysis.

RESULTS

One hundred and twenty-eight patients (1.3 %) developed secondary cancers within a median follow-up of 8.4 years. The cumulative incidence rate was 1.1 % (95 % confidence interval [CI] 0.9-1.4) at 10 years and 2.6 % (95 % CI 2.1-3.3) at 20 years after primary cancer diagnosis. Sensitivity analysis, limited to 5-year survivors (n = 5,387), confirmed these low incidence rates. The SIR of secondary cancers was 12.1 (95 % CI 10.1-14.4). In the Cox analysis, the hazard ratios for secondary cancers were 3.81 (95 % CI 1.53-9.47) for retinoblastoma, 2.78 (95 % CI 1.44-5.38) for bone/soft tissue sarcomas, and 1.81 (95 % CI 1.16-2.83) for allogeneic stem cell transplantation.

CONCLUSIONS

The cumulative incidence of secondary cancers in children in Japan was not high; however, the SIR was relatively high. Retinoblastoma or sarcoma in addition to allogeneic stem cell transplantation were significant risk factors for secondary cancers.

The NF1 gene revisited - from bench to bedside

Neurofibromatosis type 1 (NF1) is a relatively common tumour predisposition syndrome related to germline aberrations of NF1, a tumour suppressor gene. The gene product neurofibromin is a negative regulator of the Ras cellular proliferation pathway, and also exerts tumour suppression via other mechanisms.

Recent next-generation sequencing projects have revealed somatic NF1 aberrations in various sporadic tumours. NF1 plays a critical role in a wide range of tumours. NF1 alterations appear to be associated with resistance to therapy and adverse outcomes in several tumour types.

Identification of a patient's germline or somatic NF1 aberrations can be challenging, as NF1 is one of the largest human genes, with a myriad of possible mutations. Epigenetic factors may also contribute to inadequate levels of neurofibromin in cancer cells.

Clinical trials of NF1-based therapeutic approaches are currently limited. Preclinical studies on neurofibromin-deficient malignancies have mainly been on malignant peripheral nerve sheath tumour cell lines or xenografts derived from NF1 patients. However, the emerging recognition of the role of NF1 in sporadic cancers may lead to the development of NF1-based treatments for other tumour types. Improved understanding of the implications of NF1 aberrations is critical for the development of novel therapeutic strategies.

Apoptosis for prediction of radiotherapy late toxicity: lymphocyte subset sensitivity and potential effect of TP53 Arg72Pro polymorphism

We tested apoptosis levels in in vitro irradiated T-lymphocytes from breast cancer (BC) patients with radiotherapy-induced late effects. Previous results reported in the literature were revised. We also examined the effect of TP53 Arg72Pro polymorphism on irradiation-induced apoptosis (IA). Twenty BC patients, ten with fibrosis and/or telangiectasias and ten matched controls with no late reactions, were selected from those receiving radiotherapy between 1993 and 2007. All patients were followed-up at least 6 years after radiotherapy. Using the combination of both CD3 and CD8 antibodies the in vitro IA was measured in CD3, CD8 and CD4 T-lymphocytes, and CD8 natural killer lymphocytes (CD8 NK) by flow cytometry. The TP53 Arg72Pro genotype was determined by sequencing. Patients with late radiotherapy toxicity showed less IA for all T-lymphocytes except for the CD8 NK. CD8 NK showed the highest spontaneous apoptosis and the lowest IA. IA in patients with toxicity appears to be lower than the control patients only in TP53 Arg/Arg patients (P = 0.077). This difference was not present in patients carrying at least one Pro allele (P = 0.8266). Our data indicate that late side effects induced by radiotherapy of BC are associated to low levels of IA. CD8 NK cells have a different response to in vitro irradiation compared to CD8 T-lymphocytes. It would be advisable to distinguish the CD8 NK lymphocytes from the pool of CD8+ lymphocytes in IA assays using CD8+ cells. Our data suggest that the 72Pro TP53 allele may influence the IA of patients with radiotherapy toxicity.

Mutational Analysis of Ionizing Radiation Induced Neoplasms

Ionizing radiation (IR) is a mutagen that promotes tumorigenesis in multiple exposure contexts. One severe consequence of IR is the development of second malignant neoplasms (SMNs), a radiotherapy-associated complication in survivors of cancers, particularly pediatric cancers. SMN genomes are poorly characterized, and the influence of genetic background on genotoxin-induced mutations has not been examined. Using our mouse models of SMNs, we performed whole exome sequencing of neoplasms induced by fractionated IR in wild-type and Nf1 mutant mice. Using non-negative matrix factorization, we identified mutational signatures that did not segregate by genetic background or histology. Copy-number analysis revealed recurrent chromosomal alterations and differences in copy number that were background dependent. Pathway analysis identified enrichment of non-synonymous variants in genes responsible for cell assembly and organization, cell morphology, and cell function and maintenance. In this model system, ionizing radiation and Nf1 heterozygosity each exerted distinct influences on the mutational landscape.

Monoallelic loss of the imprinted gene Grb10 promotes tumor formation in irradiated Nf1+/- mice

Imprinted genes are expressed from only one parental allele and heterozygous loss involving the expressed allele is sufficient to produce complete loss of protein expression. Genetic alterations are common in tumorigenesis but the role of imprinted genes in this process is not well understood. In earlier work we mutagenized mice heterozygous for the Neurofibromatosis I tumor suppressor gene (NF1) to model radiotherapy-associated second malignant neoplasms that arise in irradiated NF1 patients. Expression analysis of tumor cell lines established from our mouse models identified Grb10 expression as widely absent. Grb10 is an imprinted gene and polymorphism analysis of cell lines and primary tumors demonstrates that the expressed allele is commonly lost in diverse Nf1 mutant tumors arising in our mouse models. We performed functional studies to test whether Grb10 restoration or loss alter fundamental features of the tumor growth. Restoring Grb10 in Nf1 mutant tumors decreases proliferation, decreases soft agar colony formation and downregulates Ras signaling. Conversely, Grb10 silencing in untransformed mouse embryo fibroblasts significantly increased cell proliferation and increased Ras-GTP levels. Expression of a constitutively activated MEK rescued tumor cells from Grb10-mediated reduction in colony formation. These studies reveal that Grb10 loss can occur during in vivo tumorigenesis, with a functional consequence in untransformed primary cells. In tumors, Grb10 loss independently promotes Ras pathway hyperactivation, which promotes hyperproliferation, an early feature of tumor development. In the context of a robust Nf1 mutant mouse model of cancer this work identifies a novel role for an imprinted gene in tumorigenesis.

Cancer-causing mutations typically involve either allele inherited from parents, and the parental source of a mutant allele is not known to influence the cancer phenotype. Imprinted genes are a class of genes whose expression is determined by a specific parental allele, either maternally or paternally derived. Thus, in contrast to most genes, the pattern of inheritance (maternal or paternal-derived) strongly influences the expression of an imprinted gene. Furthermore, imprinted genes can be differentially expressed in different tissue types. This work identifies a novel link between cancer and Grb10, an imprinted gene involved in organismal metabolism and growth. In our mouse model of radiation-induced tumors, we found monoallelic Grb10 gene loss involving the parental allele responsible for protein expression. Tumors harboring genetic loss of the expressed Grb10 allele showed absent transcript and total protein levels, despite an intact remaining wildtype Grb10 allele identified by sequencing. When restored, Grb10 suppressed tumor growth by down-regulating Ras signaling. This work demonstrates a new role for an imprinted gene in tumor formation, and shows that Grb10 functions to negatively regulate Ras signaling and suppress hyperproliferation.

Radiotherapy-induced malignancies: review of clinical features, pathobiology, and evolving approaches for mitigating risk

One of the most significant effects of radiation therapy on normal tissues is mutagenesis, which is the basis for radiation-induced malignancies. Radiation-induced malignancies are late complications arising after radiotherapy, increasing in frequency among survivors of both pediatric and adult cancers. Genetic backgrounds harboring germline mutations in tumor suppressor genes are recognized risk factors. Some success has been found with using genome wide association studies to identify germline polymorphisms associated with susceptibility. The insights generated by genetics, epidemiology, and the development of experimental models are defining potential strategies to offer to individuals at risk for radiation-induced malignancies. Concurrent technological efforts are developing novel radiotherapy delivery to reduce irradiation of normal tissues, and thereby, to mitigate the risk of radiation-induced malignancies. The goal of this review is to discuss epidemiologic, modeling, and radiotherapy delivery data, where these lines of research intersect and their potential impact on patient care.

Aetiology, genetics and prevention of secondary neoplasms in adult cancer survivors

Second and higher-order malignancies now comprise about 18% of all incident cancers in the USA, superseding first primary cancers of the breast, lung, and prostate. The occurrence of second malignant neoplasms (SMN) is influenced by a myriad of factors, including the late effects of cancer therapy, shared aetiological factors with the primary cancer (such as tobacco use, excessive alcohol intake, and obesity), genetic predisposition, environmental determinants, host effects, and combinations of factors, including gene-environment interactions. The influence of these factors on SMN in survivors of adult-onset cancer is reviewed here. We also discuss how modifiable behavioural and lifestyle factors may contribute to SMN, and how these factors can be managed. Cancer survivorship provides an opportune time for oncologists and other health-care providers to counsel patients with regard to health promotion, not only to reduce SMN risk, but to minimize co-morbidities. In particular, the importance of smoking cessation, weight control, physical activity, and other factors consonant with adoption of a healthy lifestyle should be consistently emphasized to cancer survivors. Clinicians can also play a critical role by endorsing genetic counselling for selected patients and making referrals to dieticians, exercise trainers, and others to assist with lifestyle change interventions.