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Platinum exposure and cause‐specific mortality among patients with testicular cancer

Background Although testicular cancer (TC) treatment has been associated with severe late morbidities, including second malignant neoplasms (SMNs) and ischemic heart disease (IHD), cause‐specific excess mortality has been rarely studied among patients treated in the platinum era. Methods In a large, multicenter cohort including 6042 patients with TC treated between 1976 and 2006, cause‐specific mortality was compared with general population mortality rates. Associations with treatment were assessed with proportional hazards analysis. Results With a median follow‐up of 17.6 years, 800 patients died; 40.3% of these patients died because of TC. The cumulative mortality was 9.6% (95% confidence interval [CI], 8.5%‐10.7%) 25 years after TC treatment. In comparison with general population mortality rates, patients with nonseminoma experienced 2.0 to 11.6 times elevated mortality from lung, stomach, pancreatic, rectal, and kidney cancers, soft‐tissue sarcomas, and leukemia; 1.9‐fold increased mortality (95% CI, 1.3‐2.8) from IHD; and 3.9‐fold increased mortality (95% CI, 1.5‐8.4) from pneumonia. Seminoma patients experienced 2.5 to 4.6 times increased mortality from stomach, pancreatic, bladder cancer and leukemia. Radiotherapy and chemotherapy were associated with 2.1 (95% CI, 1.8‐2.5) and 2.5 times higher SMN mortality (95% CI, 2.0‐3.1), respectively, in comparison with the general population. In a multivariable analysis, patients treated with platinum‐containing chemotherapy had a 2.5‐fold increased hazard ratio (HR; 95% CI, 1.8‐3.5) for SMN mortality in comparison with patients without platinum‐containing chemotherapy. The HR for SMN mortality increased 0.29 (95% CI, 0.19‐0.39) per 100 mg/m2 platinum dose administered (P trend < .001). IHD mortality was increased 2.1‐fold (95% CI, 1.5‐4.2) after platinum‐containing chemotherapy in comparison with patients without platinum exposure. Conclusions Platinum‐containing chemotherapy is associated with a dose‐dependent increase in the risk of SMN mortality.


INTRODUCTION
The prognosis of testicular cancer (TC) has greatly improved since the late 1970s because of the introduction of cisplatin-containing combination chemotherapy for disseminated TC, improvements in radiation techniques, and better supportive care. 1,2 Currently, in Europe, the 10-year TC-specific survival is higher than 95%. 1 TC treatment may, however, cause detrimental long-term health effects for TC survivors. Previous studies have shown that radiotherapy is associated with increased morbidity [3][4][5][6][7]
Few studies have assessed long-term cause-specific excess mortality after TC treatment. In a large, international cohort study including 1-year TC survivors (n = 38,907), Fossa et al 15 14 found increased CVD mortality only in the first year after chemotherapy for nonseminoma. They also reported increased mortality due to pneumonia and influenza in comparison with the general population, whereas Fossa et al observed an increased risk of death due to fibrosis and pneumonitis. 14,15 Since the 1980s, TC treatment intensity has gradually been reduced with decreases in the radiotherapy field size and dose among patients with seminoma, with the introduction of surveillance for stage I disease, and with fewer cycles of chemotherapy for patients with nonseminoma. 2,10,16,17 The impact of these changes on causespecific excess mortality among more recently treated TC survivors is not yet clear. Therefore, we examined cause-specific mortality within a large, multicenter Dutch cohort of patients with TC diagnosed in the cisplatin era between 1976 and 2006.

Study Population and Design
A hospital-based cohort was established that included 6124 patients with TC who were younger than 50 years at their TC diagnosis and were treated in 13 Dutch hospitals between 1976 and 2006 (Supporting Fig. 1). [5][6][7][8]10 The primary treatment was known for all patients. For efficiency reasons, we used a case-cohort design to facilitate detailed treatment data collection while allowing the assessment of multiple outcomes. 18 A hospital-stratified subcohort composing 15% of the base cohort (25% in the coordinating hospitals Antoni van Leeuwenhoek and University Medical Center Groningen) was randomly selected. Before the analysis, 82 patients without followup for vital status were excluded, and this left 6042 patients in the full cohort and 1138 patients in the randomly selected subcohort for analysis.
We established vital status up to July 2016 for 93.7% of the patients through linkage with the Dutch Central Bureau for Genealogy, which collects genealogic information on all Dutch inhabitants, including the date of death. For 378 patients (6.3%), the linkage failed, and the vital status was obtained from the patient's general practitioner (GP) and/or tumor registries. Information on the cause of death was retrieved from hospital tumor registries, the patient's medical chart, and the GP and through linkage with the nationwide cause of death registry at Statistics Netherlands up to January 1, 2016. Direct and indirect causes of death were (re)coded according to the International Classification of Diseases, Tenth Revision.
For all patients in the subcohort and for all patients who had developed a predefined event (SMN, including contralateral TC; ischemic heart disease [IHD]; heart failure; or diabetes mellitus) and were not part of the subcohort, detailed treatment data were abstracted from the medical charts; these data included chemotherapy regimens, cumulative doses and numbers of cycles, and radiotherapy fields and doses for primary treatment as well as relapse treatment. The study protocol was submitted to the institutional review board of the Netherlands Cancer Institute, which waived the requirement for individual patient consent.
All patients underwent an orchidectomy. For early-stage seminoma, orchidectomy was usually followed by radiotherapy, [16][17][18][19] which was typically given to the infradiaphragmatic para-aortic, ipsilateral iliac, and inguinal lymph nodes, with doses to delineated treatment fields ranging from 30 to 35 Gy. Since the mid-1980s, radiation doses have gradually decreased to 26 to 32 Gy. 19 Patients with stage II to IV seminoma and nonseminoma were primarily treated with cisplatin-containing combination chemotherapy (initially with cisplatin, vinblastine, and bleomycin and since the mid-1980s with bleomycin, etoposide, and cisplatin [BEP]). 20 Although rare, 1.8% of the patients (n = 10) in the subcohort who were treated with chemotherapy (mainly patients with nonseminoma) were treated with vinblastine, bleomycin, dactinomycin, or a combination of these drugs between 1976 and 1980. Surveillance after orchidectomy was standard treatment for stage I nonseminoma from 1984 onward in most hospitals. 21

Statistical Analysis
The time at risk started at the TC diagnosis and ended at the date of death, the date of emigration, or January 1, 2016 (whichever came first). Mortality rates among patients with TC were compared with age-specific, calendar period-specific, and site-specific cancer mortality rates in Cancer February 1, 2020 the Dutch male population. Standardized mortality ratios (SMRs), absolute excess mortality (expressed per 10,000 person-years), and corresponding 95% confidence intervals (CIs) were computed with standard methods and are reported for the full cohort. 18 General population mortality data from Statistics Netherlands for 1976-2015 were used as reference rates. Unless otherwise stated, TC mortality was excluded from analyses. Tests for homogeneity and trends of SMRs were performed within collapsed person-time Poisson regression models; models were adjusted for age unless specified otherwise. 22 Missing information on stage (7.5%), primary and follow-up treatment (radiotherapy [0.8%], radiotherapy field [13.5%], radiotherapy dose [11.8%], chemotherapy [0.8%], chemotherapy regimen [5.1%], and number of cycles [11.3%]), and weight, height, and smoking status at the TC diagnosis (11.9%) were imputed for the cases and subcohort members via ordered multiple imputation by chained equations with 20 data sets and with patient clusters ignored. 19,20 Our results are based on administered chemotherapy and radiation doses. Multinomial models and linear regression models were used for imputation; the year and age at treatment, histology, age, hospital, and cause-specific cumulative hazards of mortality calculated with a Cox regression model before imputation were included as extra covariates. 20 Because of the amount of missing data on body size area and cumulative platinum dose, we based the administered platinum dose on the number of administered cycles, which agreed well with actual cumulative administered doses in milligrams per meter squared of body surface area in patients without missing data.
Cumulative mortality was estimated with death due to TC as a competing risk, 23 and trends over time were evaluated via competing risk regression models with adjustments for the age at TC diagnosis. Multivariable proportional hazards models were used to assess associations of TC treatment with cause-specific mortality. The time since TC treatment was used as the time scale, and the partial likelihood function was adjusted for the case-cohort analysis with Barlow's inverse probability weights. [18][19][20][21][22][23] Treatment was included time-dependently, and this allowed a patient to add person-time to a different treatment category at the date on which treatment for relapsed or contralateral TC was initiated. 23 All analyses were adjusted for age and smoking unless stated otherwise. For a sensitivity analysis, we evaluated the effect of clustering of patients within a treatment center by adding a clustering term to the Cox models, and we adjusted the variance for within-treatment center clustering. To assess excess relative risk by the administered treatment dose, the linear increase in the hazard ratio (HR) for dose categories (estimated from a Cox model with the category value set at the median dose within that category) was estimated via variance-weighted least squares regression with weights equal to 1/variance of the HR for each imputed data set. We assessed dose-response relationships by first modeling the cause-specific HRs as HR = 1 + β(dose), where β is the proportional increase in the HR per unit increase in dose. We evaluated a departure from linearity by including a quadratic dose term in the model HR = 1 + β(dose) + Φ(dose) 2 and testing whether the coefficient for the quadratic dose term was Φ = 0. Regression model estimates were pooled with Rubin's rule. 24,25 The proportional hazards assumption was assessed with residual-based methods. Standard errors are reported as robust standard errors. A P value ≤ .05 was considered significant. Stata statistical software (StataCorp LP, College Station, Texas; 2013) was used for analysis.

RESULTS
The cohort comprised 2875 patients with seminoma and 3167 patients with nonseminoma (Table 1

Comparisons With the General Population
The cause of death was available for 96.1% of all 800 patients who had died up to January 1, 2016 (Table 2). Of these 800 patients, 322 (40.3%) died of TC, 226 (28.3%) died of SMNs other than TC, and 104 (13.0%) died of diseases of the circulatory system. Non-TC mortality was 1.4-fold increased (95% CI, 1.3-1.6) in comparison with general population mortality rates. We observed 28.9 excess deaths from TC (95% CI, 25.8-32.3) and 13.0 excess deaths due to causes other than TC (95% CI, 9.1-17.1) per 10,000 person-years of follow-up. In the univariate analysis, SMRs for non-TC mortality decreased among older patients (P trend < .001; Supporting Tables 1 and 2). SMRs for non-TC mortality and SMN mortality remained increased even 20 or more years after treatment in comparison with general population rates, without a clear trend in SMRs (P trend = .24 for non-TC mortality; P trend = .49 for SMN mortality; Supporting Table 1). Adjusted for age and follow-up duration, Cancer February 1, 2020 SMRs for non-TC mortality and SMN mortality did not decrease among more recently treated patients (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) in comparison with those treated between 1976 and 1985 and between 1986 and 1995 (P trend = .49 for non-TC mortality; P trend = .80 for SMN mortality; Supporting Table 3). However, SMRs for noncancer mortality did decrease over time (P < .001).

Cause-Specific Mortality and TC Treatment: Case-Cohort Analysis
In a multivariable analysis, platinum-containing chemotherapy was associated with 2.5 times increased SMN mortality (95% CI, 1.8-3.5) in comparison with surgery only, whereas GI tract SMN mortality was 3.1-fold increased (95% CI, 1.7-5.7) among platinum-treated patients (Table 3). Both colorectal (P trend = .006) and noncolorectal GI tract SMN mortality (P trend < .001) increased with a higher dose of cisplatin-containing chemotherapy, with the receipt of platinum-containing chemotherapy at 400 to 499 and ≥500 mg/m 2 being associated with 2.4 and 6.4 times increased noncolorectal GI cancer mortality, respectively, in comparison with patients not receiving platinum-containing chemotherapy. A dose-response relationship was observed between SMN mortality and the cumulative administered platinum dose in particular for GI tract SMNs (Fig. 2)  Cancer February 1, 2020 times (95% CI, 0.9-4.1) after chemotherapy and tended to increase with an increasing administered dose of platinum-containing chemotherapy (P trend = .076). Smoking at the TC diagnosis was an independent risk factor associated with 3.8 times increased lung cancer mortality (95% CI, 1.7-8.5). IHD mortality increased 2.1 times (95% CI, 1.5-4.2) after platinum-containing chemotherapy in comparison with patients without platinum exposure. IHD mortality also increased 3.4 times (95% CI, 1.4-8.3) among patients who smoked at the TC diagnosis. The infradiaphragmatic radiation dose was also associated with increasing SMN mortality (P trend < .001). Noncolorectal GI tract SMN mortality also increased with a higher infradiaphragmatic radiation dose. The administered infradiaphragmatic radiation dose showed a linear dose-response relationship, with the HR for any SMN increasing by 0.05 (95% CI, 0.03-0.07; P trend ≤ .001) and the HR for GI tract SMN mortality increasing by 0.12 (95% CI, 0.09-0.15; P trend ≤ .001) per gray of radiation administered (Fig. 3).
A complete case analysis, including only patients with nonmissing treatment data, showed similar results in comparison with the analysis incorporating imputed data. A sensitivity analysis with clustering on treatment center showed similar results for treatment-associated risks (Supporting Table 5).

DISCUSSION
In this large, multicenter cohort of Dutch patients with TC treated between 1976 and 2006, we observed increased mortality from SMNs as well as causes other than cancer, particularly IHD. Although a few studies previously reported increased mortality from solid SMNs, leukemia, and CVD among patients with TC, our study is the first to report that an increasing administered platinum dose is associated with a linearly increasing risk of SMN mortality, particularly mortality due to GI cancer. 6,8,15,[26][27][28] Our study further adds to mortality estimates in previous studies by including primary and follow-up treatment and providing mortality risk estimates after more prolonged follow-up of patients treated with platinum-containing chemotherapy.
Both chemotherapy and radiotherapy have previously been associated with an increased risk of various solid SMNs, including GI and urologic malignancies. 5,6,19,26,29,30 Radiotherapy and chemotherapy were associated with SMN mortality (SMR for radiotherapy, 2.1; 95% CI, 1.8-2.5; SMR for chemotherapy, 2.5; 95% CI, 2.0-3.1). Our observation of an increasing risk of mortality due to SMNs with a higher cumulative dose of platinum-based chemotherapy is consistent with a dose-dependent increase in the solid SMN incidence, which we recently reported. 10 Kier et al 6 also recently . HR estimates (ERRs) were derived from models adjusted for age (continuous), smoking at testicular cancer diagnosis, supradiaphragmatic radiotherapy, and subdiaphragmatic radiation dose. Circles represent HR estimates for dose categories (no platinum-containing CT and >0-399, 400-499, and ≥500 mg/m 2 of body surface area) and are plotted at the median dose in each category (0, 300, 400, and 600 mg/m 2 , respectively). Dose-response relationships were based on the categorical dose as an outcome, with the category set at the median dose within that category. Vertical lines reflect the 95% CIs around the HRs for dose categories. The dashed line in panel A is the best fitting dose-response relationship and reflects a linear increase in the mortality risk from any SMN, with 0.29 (95% CI, 0.19-0.39; P < .001) added to the HR for each additional platinum-containing CT dose of 100 mg/m 2 body surface area. The dashed line in panel B is the best fitting dose-response relationship and reflects a linear increase in gastrointestinal SMN mortality risk, with 0.66 (95% CI, 0.35-0.97; P < .001) added to the HR for each additional platinum-containing CT dose of 100 mg/m 2 of body surface area. CI indicates confidence interval; CT, chemotherapy; ERR, excess relative risk; HR, hazard ratio; SMN, second malignant neoplasm.
Cancer February 1, 2020 reported 1.6-fold increased SMN mortality among patients with TC treated with platinum-containing chemotherapy; risks were up to 5.8-fold increased among patients treated with multiple lines of treatment in comparison with general population controls. In their study, BEP chemotherapy was associated with increased mortality from lung, esophageal, and bladder cancers, softtissue sarcomas, and myeloid leukemia. We confirm their findings, but our observations include renal cancer rather than bladder cancer.
Cisplatin has been classified as a carcinogenic compound and acts by crosslinking DNA. 31,32 Previously, increased GI cancer incidence among childhood cancer survivors has been reported after platinum exposure. [33][34][35] Exposure to platinum-containing chemotherapy has been suggested to cause GI polyposis in humans, although the causal mechanism has not yet been established. 36 Increased mortality from soft-tissue sarcomas was observed among patients with nonseminoma. Our results are in line with those of Kier et al, 6 who observed an increased risk of soft-tissue sarcoma after the receipt of BEP (median time, 12 years), whereas no increased risks were observed after radiotherapy. Our soft-tissue sarcoma cases died after a median follow-up of 10.6 years after primary TC. We cannot exclude the idea that the high SMR for sarcomas is partly due to late relapses, however rare. 37 Radiotherapy was also associated with increased mortality from non-TC SMNs, and mortality remained increased throughout follow-up. Previous studies, which largely consisted of patients treated before the 1980s, found a 1.5 to 1.9 times increased SMR from SMNs after radiotherapy. 8,26,27 Excess mortality among irradiated patients with seminoma followed beyond 15 years is consistent with a radiation effect. 8,26 Robinson et al 4 observed excess cancer mortality only within the first 5 years after the diagnosis among patients treated with modern radiation techniques since the 1990s. A more recent Danish population-based study observed 2.1 times increased SMN mortality, particularly from stomach, pancreatic, prostate, and bladder cancers, after radiation for TC between 1984 and 2007. 6 Except for prostate cancer, we also observed increased mortality for these malignancies in our patients with seminoma.
A substantial proportion of all cancer deaths in our cohort among patients with seminoma was attributable to pancreatic cancer (18 deaths; 31% of SMN-related excess deaths), a malignancy with a poor prognosis that has not improved much over the last decades. A recent study already reported a strongly increasing SMN risk with higher radiation doses to the pancreas (excess relative risk, 0.12 per gray of radiation). 30 Because few patients with seminoma nowadays undergo para-aortic radiation and radiation doses for these patients are also generally lower (<26 Gy), radiation-associated pancreatic cancer mortality will likely decrease in the near future. On the SMNs by the administered infradiaphragmatic RT dose. HR estimates (ERRs) were derived from models adjusted for age (continuous), smoking at testicular cancer diagnosis, supradiaphragmatic RT, and platinum dose. Dose-response relationships were based on the categorical dose as an outcome, with the category set at the median dose within that category. Circles represent estimates for dose categories (no infradiaphragmatic RT and >0-26, 27-32, 33-36 Gy, and >36 Gy) and are plotted at the median dose in each category (0, 26, 30, 36, and 40 Gy, respectively). Vertical lines denote the 95% CIs around the HRs for dose categories. The dashed line in panel A is the best fitting dose-response relationship and reflects a linear increase in SMN mortality, with 0.05 (95% CI, 0.03-0.07; P < .001) added to the HR for each additional gray of infradiaphragmatic RT. The dashed line in panel B is the best fitting dose-response relationship and reflects a linear increase in gastrointestinal mortality, with 0.12 (95% CI, 0.09-0.15; P < .001) added to the mortality rate for each additional gray of infradiaphragmatic RT. CI indicates confidence interval; ERR, excess relative risk; HR, hazard ratio; RT, radiotherapy; SMN, second malignant neoplasm.
Cancer February 1, 2020 other hand, we recently reported that platinum-containing chemotherapy may also increase pancreatic cancer risk. 9 IHD mortality was associated with the receipt of platinum-containing chemotherapy in our study. In line with our findings, chemotherapy exposure increased circulatory disease mortality 1.4-fold in a large, international registry-based study including 38,907 patients treated after 1975. 15 Kier et al 6 noted borderline significantly increased circulatory disease mortality after the receipt of chemotherapy in comparison with the general population in Danish patients treated between 1984 and 2007. Interestingly, Fung et al 14 recently observed increased CVD mortality only during the first year of follow-up (based on only 6 cardiac deaths and 5 cerebrovascular disease deaths), although the median follow-up was only 6.5 years after chemotherapy in their study. Some case reports have described severe acute myocardial infarction 38,39 or stroke shortly after chemotherapy in TC survivors, 40 although these events are rare and usually not fatal. Differences in the underlying CVD risk factors, lifestyles, and prophylactic use of low-molecular-weight heparin to prevent platinum-associated thromboembolic events may underlie these heterogeneous findings with respect to CVD mortality. 41,42 We found increased mortality from respiratory diseases, particularly pneumonia, after exposure to chemotherapy in our cohort. Our results are in line with those of Fossa et al, 15 who observed increased respiratory mortality due to lung fibrosis and pneumonitis among patients treated with primary chemotherapy after 1975. To our knowledge, bleomycin has not been associated with side effects other than lung fibrosis. Unfortunately, because the current study did not include sufficient numbers of patients who did not receive bleomycin (ie, patients treated with etoposide and platinum), we cannot completely ascribe the increased mortality risks to platinum exposure alone.
Strong features of the current study include its extended follow-up and the availability of detailed treatment data. Using time-dependent Cox regression, we were able to more precisely allocate observation time to primary and follow-up treatment, and this increased the reliability of our results in comparison with other studies based on primary treatment only. Limitations include the lack of risk factors for cancer and cardiovascular mortality (ie, lifestyle and smoking), although smoking behavior in our cohort is not likely to differ from that of the general population. 15 In addition, our analysis did not allow further analysis for genitourinary malignancies because of the low numbers of cases exposed to platinum. Despite our efforts to abstract compete treatment exposure information from the medical records, we had missing data on, among other things, the cumulative platinum dose and body size. However, because dose reductions were rare and the actual cumulative administered dose for patients for whom we had complete information on dose and body surface was highly comparable to the dose based on the number of administered cycles of chemotherapy, in all our analyses, we approximated the cumulative platinum dose with the number of administered cycles of chemotherapy. We acknowledge that we present many significance tests and, therefore, caution against overinterpretation of our findings, especially when they are based on P values > .001.
For 191 of the 226 patients (84.5%) who died of an SMN and for 31 of the 51 patients (60.8%) who died of IHD, detailed treatment data were available from the medical records. For most of the patients who had died of an SMN and for whom detailed treatment data were missing, the date of death was later than the date of last linkage with the Netherlands Cancer Registry and the date of last information from the GP. We also identified 18 new fatal IHD events (among the 51 patients who died of IHD) among patients without a known IHD history. For these patients, either the GP had not responded to our request for information or the date of death was later than the date of the last medical information that we had received from the GP. In the Netherlands, unfortunately, tracing back patients identified on the basis of data provided by the cause of death registry at Statistics Netherlands is not allowed because of the privacy laws. For these patients, treatment details were imputed.
Despite efforts to reduce the long-term toxicity of TC treatment, we observed no decrease in overall excess mortality or mortality due to cancers other than TC among more recently treated patients, although absolute excess mortality only modestly increased after 1995. However, noncancer mortality decreased over time. Fossa et al 15 previously reported a significantly increased SMR from causes other than cancer of 1.07 for patients treated before 1975 and of 1.04 for patients treated after 1975 in comparison with general population rates, and this indicated only a small mortality reduction over time. Finally, treatment-associated mortality may be partly due to (interactions with) environmental and lifestyle factors that also operate in the general population.
In conclusion, TC survivors treated in the platinum era experience increased mortality from SMNs in comparison with the general population, and this appears in part due to exposure to platinum-containing chemotherapy. This study also shows that exposure to Cancer February 1, 2020 platinum-containing chemotherapy is associated not only with a dose-dependent increased SMN incidence but also increased mortality from SMNs. Future studies and more prolonged follow-up of patients treated more recently with 3 or fewer (B)EP cycles are needed to better assess whether low platinum doses indeed still increase the risk for non-TC mortality. In the meantime, potential strategies toward risk reduction (ie, screening for malignancies of the GI tract as well as [risk factors for] CVDs) are warranted among long-term survivors treated with higher doses of platinum or para-aortic radiation. In addition, through healthier lifestyle behaviors (particularly smoking cessation, reduction of alcohol intake, increased physical activity, and a healthy diet), mortality may be reduced.

FUNDING SUPPORT
This work was supported by the Dutch Cancer Society (grant 2011-5209).