Meta-analysis of second cancer risk after radiotherapy among childhood cancer survivors

The risk of cancer following high, and very high, doses of ionising radiation

It is established that moderate-to-high doses of ionising radiation increase the risk of subsequent cancer in the exposed individual, but the question arises as to the risk of cancer from higher doses, such as those delivered during radiotherapy, accidents, or deliberate acts of malice. In general, the cumulative dose received during a course of radiation treatment is sufficiently high that it would kill a person if delivered as a single dose to the whole body, but therapeutic doses are carefully fractionated and high/very high doses are generally limited to a small tissue volume under controlled conditions. The very high cumulative doses delivered as fractions during radiation treatment are designed to inactivate diseased cells, but inevitably some healthy cells will also receive high/very high doses. How the doses (ranging from <1 Gy to tens of Gy) received by healthy tissues during radiotherapy affect the risk of second primary cancer is an increasingly important issue to address as more cancer patients survive the disease. Studies show that, except for a turndown for thyroid cancer, a linear dose-response for second primary solid cancers seems to exist over a cumulative gamma radiation dose range of tens of gray, but with a gradient of excess relative risk per Gy that varies with the type of second cancer, and which is notably shallower than that found in the Japanese atomic bomb survivors receiving a single moderate-to-high acute dose. The risk of second primary cancer consequent to high/very high doses of radiation is likely to be due to repopulation of heavily irradiated tissues by surviving stem cells, some of which will have been malignantly transformed by radiation exposure, although the exact mechanism is not known, and various models have been proposed. It is important to understand the mechanisms that lead to the raised risk of second primary cancers consequent to the receipt of high/very high doses, in particular so that the risks associated with novel radiation treatment regimens-for example, intensity modulated radiotherapy and volumetric modulated arc therapy that deliver high doses to the target volume while exposing relatively large volumes of healthy tissue to low/moderate doses, and treatments using protons or heavy ions rather than photons-may be properly assessed.

Secondary chronic myeloid leukemia following acute myeloid leukemia treated with autologous hematopoietic stem cell transplantation: a case report

OBJECTIVE

Acute myeloid leukemia (AML) is a hematopoietic stem cell malignancy and the most common type of leukemia, with the 5-year relative survival rate of 19% in Europe. Chronic myeloid leukemia (CML) is a slowly progressive clonal malignant disease, and a myeloproliferative disorder which is derived from biphasic hematopoietic stem cells but driven by progenitor cells. AML following CML is common, which can be caused by an antecedent myeloid malignancy, leukemogenic therapy, or without an identifiable prodrome or exposure to cytotoxic agents. However, the case of secondary chronic myeloid leukemia following acute myeloid leukemia treated with autologous hematopoietic stem cell transplantation is rare.

METHODS

Here we report a unique case of secondary CML after AML treated by chemotherapy and autologous peripheral blood stem cell transplantation. The 34-year-old male was diagnosed with AML subtype M5b according to clinical features in 2011. The patient was treated with the MAE program (mitoxantrone, cytosine arabinoside, etoposide) for two courses, followed by the IAE program (idarubicin, cytosine arabinoside, etoposide) and cytosine arabinoside for consolidation chemotherapy. An autologous hematopoietic stem cell transplantation with prophylactic intrathecal methotrexate cytarabine and dexamethasone was initiated.

RESULTS

Subsequently, the patient achieved complete remission in 2012. After 4 years, the patient presented with leukocyte elevation of more than 4 months, and then was diagnosed with secondary CML. Based on this diagnosis, and with respect to the patient's severely compromised overall condition, tyrosine kinase inhibitors (TKI) therapy was conducted in 2016. The patient achieved, and continue to be in, complete remission.

CONCLUSIONS

The case expands the understanding of secondary CML and emphasizes the importance of oncological vigilance in patients with secondary CML after AML therapy.

Risk of second primary tumors in GIST survivors: A systematic review and meta-analysis

INTRODUCTION

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal tumors arising in the gastrointestinal tract. Second primary tumors (SPTs) have been reported frequently, either synchronously or during follow-up, in patients diagnosed with GISTs.

METHODS

We carried out an electronic search of PubMed, SCOPUS, Web of Science, EMBASE, and the Cochrane Library seeking articles investigating the incidence of SPTs in patients with concomitant GIST. All studies were evaluated for heterogeneity before meta-analysis and for publication bias. Pooled incidence rate was estimated using fixed- and random-effects models. Subsite of SPTs was also investigated.

RESULTS

A total of 32 studies met the inclusion criteria, for a total of 19,627 patients with a diagnosis of GIST. The pooled prevalence of SPTs was 20%, with 14% and 3% being synchronous and metachronous tumors, respectively. We found a risk for several specific cancer sites, in particular gastrointestinal (5%) and genitourinary tract cancers (3%). The most frequently associated malignancies were: colorectal (17%), prostate (14%), gastric (9%), esophageal (5.5%), lung (5.4%), hepato-biliopancreatic (4.7%), breast (4.6%), lymphoma (4.4%), kidney (4.35%), and sarcomas (3.3%). Regression analyses revealed a significant positive association for all SPTs with follow-up and Miettinen risk.

CONCLUSIONS

Our results indicate that 20% of patients with GIST experienced a SPT, primarily synchronously with a diagnosis of GIST. In particular, we observed an excess of incident gastrointestinal tumors. These findings have important implications for both pathologists, who should perform extensive molecular analysis of surgical non-GIST specimens in resected patients, and for oncologists, who should continue to follow up GIST patients.

Risk of second cancers in the era of modern radiation therapy: does the risk/benefit analysis overcome theoretical models?

In the era of modern radiation therapy, the compromise between the reductions in deterministic radiation-induced toxicities through highly conformal devices may be impacting the stochastic risk of second malignancies. We reviewed the clinical literature and evolving theoretical models evaluating the impact of intensity-modulated radiation therapy (IMRT) on the risk of second cancers, as a consequence of the increase in volumes of normal tissues receiving low doses. The risk increase (if any) is not as high as theoretical models have predicted in adults. Moreover, the increase in out-of-field radiation doses with IMRT could be counterbalanced by the decrease in volumes receiving high doses. Clinical studies with short follow-up have not corroborated the hypothesis that IMRT would drastically increase the incidence of second cancers. In children, the risk of radiation-induced carcinogenesis increases from low doses and consequently the relative risk of second cancers after IMRT could be higher than in adults, justifying current developments of proton therapy with priority given to this population. Although only longer follow-up will allow a true assessment of the real impact of these modern techniques on radiation-induced carcinogenesis, a comprehensive risk-adapted strategy will help minimize the probability of second cancers.

Secondary malignancies in chronic myeloid leukemia patients after imatinib-based treatment: long-term observation in CML Study IV

Treatment of chronic myeloid leukemia (CML) has been profoundly improved by the introduction of tyrosine kinase inhibitors (TKIs). Long-term survival with imatinib is excellent with a 8-year survival rate of ∼88%. Long-term toxicity of TKI treatment, especially carcinogenicity, has become a concern. We analyzed data of the CML study IV for the development of secondary malignancies. In total, 67 secondary malignancies were found in 64 of 1525 CML patients in chronic phase treated with TKI (n=61) and interferon-α only (n=3). The most common malignancies (n⩾4) were prostate, colorectal and lung cancer, non-Hodgkin's lymphoma (NHL), malignant melanoma, non-melanoma skin tumors and breast cancer. The standardized incidence ratio (SIR) for all malignancies excluding non-melanoma skin tumors was 0.88 (95% confidence interval (0.63-1.20)) for men and 1.06 (95% CI 0.69-1.55) for women. SIRs were between 0.49 (95% CI 0.13-1.34) for colorectal cancer in men and 4.29 (95% CI 1.09-11.66) for NHL in women. The SIR for NHL was significantly increased for men and women. An increase in the incidence of secondary malignancies could not be ascertained. The increased SIR for NHL has to be considered and long-term follow-up of CML patients is warranted, as the rate of secondary malignancies may increase over time.

Evolving Clinical Cancer Radiotherapy: Concerns Regarding Normal Tissue Protection and Quality Assurance

Radiotherapy, which is one of three major cancer treatment methods in modern medicine, has continued to develop for a long period, more than a century. The development of radiotherapy means allowing the administration of higher doses to tumors to improve tumor control rates while minimizing the radiation doses absorbed by surrounding normal tissues through which radiation passes for administration to tumors, thereby reducing or removing the incidence of side effects. Such development of radiotherapy was accomplished by the development of clinical radiation oncology, the development of computers and machine engineering, the introduction of cutting-edge imaging technology, a deepened understanding of biological studies on the effects of radiation on human bodies, and the development of quality assurance (QA) programs in medical physics. The development of radiotherapy over the last two decades has been quite dazzling. Due to continuous improvements in cancer treatment, the average five-year survival rate of cancer patients has been close to 70%. The increases in cancer patients' complete cure rates and survival periods are making patients' quality of life during or after treatment a vitally important issue. Radiotherapy is implemented in approximately 1/3 to 2/3s of all cancer patients; and has improved the quality of life of cancer patients in the present age. Over the last century, as a noninvasive treatment, radiotherapy has unceasingly enhanced complete tumor cure rates and the side effects of radiotherapy have been gradually decreasing, resulting in a tremendous improvement in the quality of life of cancer patients.

Methodological extensions of meta-analysis with excess relative risk estimates: application to risk of second malignant neoplasms among childhood cancer survivors treated with radiotherapy

Although radiotherapy is recognized as an established risk factor for second malignant neoplasms (SMNs), the dose response of SMNs following radiotherapy has not been well characterized. In our previous meta-analysis of the risks of SMNs occurring among children who have received radiotherapy, the small number of eligible studies precluded a detailed evaluation. Therefore, to increase the number of eligible studies, we developed a method of calculating excess relative risk (ERR) per Gy estimates from studies for which the relative risk estimates for several dose categories were available. Comparing the calculated ERR with that described in several original papers validated the proposed method. This enabled us to increase the number of studies, which we used to conduct a meta-analysis. The overall ERR per Gy estimate of radiotherapy over 26 relevant studies was 0.60 (95%CI: 0.30-1.20), which is smaller than the corresponding estimate for atomic bomb survivors exposed to radiation as young children (1.7; 95% CI: 1.1-2.5). A significant decrease in ERR per Gy with increase in age at exposure (0.85 times per annual increase) was observed in the meta-regression. Heterogeneity was suggested by Cochran's Q statistic (P < 0.001), which may be partly accounted for by age at exposure.

Local radiation dose and solid second malignant neoplasms after childhood cancer in Germany: a nested case-control study

Radiotherapy (RT) has been associated with the development of solid second malignant neoplasms (SMNs) in childhood cancer survivors. The aim of this study was to analyse the effect of cumulative doses of previous RT received at the SMN body region, at all other body regions and at body regions adjacent to the SMN, on the risk of developing a solid SMN. A total of 190 cases diagnosed with a solid second malignant neoplasm in 1980-2002 were matched with 368 controls with single neoplasm from the database of the German Childhood Cancer Registry (GCCR) (33,809 patients at cut-off date). The GCCR registers approximately 97 % of all childhood malignancies which occur at an age of less than 15 years in Germany since 1980. It was found that 147 (77.4 %) cases had received RT compared to 208 (56.6 %) controls with cumulative focus doses from 8 to 110 Gy. Fifty per cent of the SMNs and 60 % of RT affected the head region. RT was shown to increase the risk of a solid second tumour within the body region of radiation by 5.3 % per Gy (odds ratio 1.053; 95 % confidence interval 1.036-1.071). With increasing age at diagnosis and with more recent treatment eras, this effect decreased. Cumulative RT doses received at all other body regions or only at body regions adjacent to the SMN did not show an additional effect on the risk of developing an SMN. It is thus concluded that RT is the main risk factor for the development of SMNs within the irradiated body region. Late effects surveillance of former patients should give special attention to the originally irradiated parts of the body.

[The issue of low doses in radiation therapy and impact on radiation-induced secondary malignancies]

Several studies have well documented that the risk of secondary neoplasms is increasing among patients having received radiation therapy as part of their primary anticancer treatment. Most frequently, radiation-induced neoplasms occur in volume exposed to high doses. However, the impact of "low" doses (<5 Gy) in radiation-induced carcinogenesis should be clinically considered because modern techniques of intensity-modulated radiation therapy (IMRT) or stereotactic irradiation significantly increase tissue volumes receiving low doses. The risk inherent to these technologies remains uncertain and estimates closely depend on the chosen risk model. According to the (debated) linear no-threshold model, the risk of secondary neoplasms could be twice higher with IMRT, as compared to conformal radiation therapy. It seems that only proton therapy could decrease both high and low doses delivered to non-target volumes. Except for pediatric tumors, for which the unequivocal risk of second malignancies (much higher than in adults) should be taken into account, epidemiological data suggest that the risk of secondary cancer related to low doses could be very low, even negligible in some cases. However, clinical follow-up remains insufficient and a marginal increase in secondary tumors could counterbalance the benefit of a highly sophisticated irradiation technique. It therefore remains necessary to integrate the potential risk of new irradiation modalities in a risk-adapted strategy taking into account therapeutic objectives but also associated risk factors, such as age (essentially), chemotherapy, or life style.

Second solid cancers after radiation therapy: a systematic review of the epidemiologic studies of the radiation dose-response relationship

Rapid innovations in radiation therapy techniques have resulted in an urgent need for risk projection models for second cancer risks from high-dose radiation exposure, because direct observation of the late effects of newer treatments will require patient follow-up for a decade or more. However, the patterns of cancer risk after fractionated high-dose radiation are much less well understood than those after lower-dose exposures (0.1-5 Gy). In particular, there is uncertainty about the shape of the dose-response curve at high doses and about the magnitude of the second cancer risk per unit dose. We reviewed the available evidence from epidemiologic studies of second solid cancers in organs that received high-dose exposure (>5 Gy) from radiation therapy where dose-response curves were estimated from individual organ-specific doses. We included 28 eligible studies with 3434 second cancer patients across 11 second solid cancers. Overall, there was little evidence that the dose-response curve was nonlinear in the direction of a downturn in risk, even at organ doses of ≥60 Gy. Thyroid cancer was the only exception, with evidence of a downturn after 20 Gy. Generally the excess relative risk per Gray, taking account of age and sex, was 5 to 10 times lower than the risk from acute exposures of <2 Gy among the Japanese atomic bomb survivors. However, the magnitude of the reduction in risk varied according to the second cancer. The results of our review provide insights into radiation carcinogenesis from fractionated high-dose exposures and are generally consistent with current theoretical models. The results can be used to refine the development of second solid cancer risk projection models for novel radiation therapy techniques.

Thyroid exposure to scattered radiation and associated second cancer risk from paediatric radiotherapy for extracranial tumours

This study was conducted to estimate the scattered thyroid dose and relevant second cancer risk from radiotherapy for extracranial tumours during childhood.  Anteroposeterior and posteronaterior field irradiations employed during the treatment of Hodgkin's disease, neuroblastoma and Wilms' tumour were simulated on two humanoid phantoms representing 5- and 10-y-old patients. Measurements were performed using thermoluminescent dosemeters. Practical thyroid lead shields with thicknesses of 2-10 mm were placed in the phantoms' neck region. The lifetime risk for cancer induction was assessed using sex- and age-specific risk factors. Thyroid dose per monitor unit varied from 28.1 to 492.4 μGy by the primary irradiation site and patient's age. The 10-mm-thick lead shield led to a dose reduction up to 28.9 %. For typical prescribed tumour doses, the total risks for thyroid cancer development after radiotherapy of 5- and 10-y-old male patients were 0.05-0.99  and 0.03-0.48 %, respectively. The corresponding risks for females increased to 0.29-5.51 and 0.17-2.94 %.