Effect of prophylactic anticoagulation on incidence of venous thromboembolism in testicular germ cell tumor patients

Background Testicular germ cell tumors (GCTs) are among the most common solid tumors in young males. With the availability of highly effective treatment, improving patients’ quality of life has gained more focus in recent years. Venous thromboembolism (VTE), commonly occurring in GCT patients, is associated with increased morbidity and mortality. Prophylactic anticoagulation has been shown to decrease the risk of VTE in patients with malignancy. The aim of this retrospective study was to evaluate the effect of low molecular weight heparin (LMWH) prophylaxis on incidence of VTE and outcome in GCT patients treated with first-line chemotherapy. Methods Our study population included chemotherapy-naive GCT patients treated with first-line chemotherapy at the National Cancer Institute, Bratislava, Slovakia from January 2000 to December 2017. VTE was defined as any venous thrombosis or pulmonary embolism, confirmed by imaging, occurring during first-line chemotherapy. Patients diagnosed with VTE on initial staging exam were excluded from the study. No visceral thromboses were observed. Results Our cohort included 353 GCT patients. LMWH prophylaxis was administered to 104 patients (29.5%), 249 patients (70.5%) did not receive prophylaxis. We observed 14 (4.0%) VTE events. The difference in VTE incidence between patients with and without prophylaxis was not statistically significant (5.8% vs. 3.2% P = 0.37). We have observed a trend to longer overall survival in patients without prophylaxis (hazard ratio = 0.61, 95% confidence interval = 0.32-1.13, P = 0.08). Patients with extragonadal GCT receiving VTE prophylaxis had significantly shorter survival. (hazard ratio = 0.29, 95% confidence interval = 0.08-1.12, P = 0.04). This effect was most likely driven by higher incidence of treatment related deaths in patients with extragonadal GCT receiving LMWH. ( P = 0.06) Conclusions LMWH prophylaxis was not associated with decreased VTE incidence. Moreover, there was a higher incidence of treatment related


Abstract
Background Testicular germ cell tumors (GCTs) are among the most common solid tumors in young males. With the availability of highly effective treatment, improving patients' quality of life has gained more focus in recent years. Venous thromboembolism (VTE), commonly occurring in GCT patients, is associated with increased morbidity and mortality. Prophylactic anticoagulation has been shown to decrease the risk of VTE in patients with malignancy. The aim of this retrospective study was to evaluate the effect of low molecular weight heparin (LMWH) prophylaxis on incidence of VTE and outcome in GCT patients treated with first-line chemotherapy.
Methods Our study population included chemotherapy-naive GCT patients treated with first-line chemotherapy at the National Cancer Institute, Bratislava, Slovakia from January 2000 to December 2017. VTE was defined as any venous thrombosis or pulmonary embolism, confirmed by imaging, occurring during first-line chemotherapy. Patients diagnosed with VTE on initial staging exam were excluded from the study. No visceral thromboses were observed.
Results Our cohort included 353 GCT patients. LMWH prophylaxis was administered to 104 patients (29.5%), 249 patients (70.5%) did not receive prophylaxis. We observed 14 (4.0%) VTE events. The difference in VTE incidence between patients with and without prophylaxis was not statistically significant (5.8% vs. 3.2% P = 0.37). We have observed a trend to longer overall survival in patients without prophylaxis (hazard ratio = 0.61, 95% confidence interval = 0.32-1.13, P = 0.08). Patients with extragonadal GCT receiving VTE prophylaxis had significantly shorter survival. (hazard ratio = 0.29, 95% confidence interval = 0.08-1.12, P = 0.04). This effect was most likely driven by higher incidence of treatment related deaths in patients with extragonadal GCT receiving LMWH. ( P = 0.06) Conclusions LMWH prophylaxis was not associated with decreased VTE incidence. Moreover, there was a higher incidence of treatment related deaths in patients with extragonadal tumor location.
LMWH prophylaxis during hospitalization should not be used routinely in GCT patients receiving chemotherapy.
Background Testicular germ cell tumors (GCTs) represent one of the most common solid neoplasms in young males between the ages of 15 and 35 and the incidence has been steadily rising in the past decades. [1,2] Cisplatin-based chemotherapy with or without resection of the residual mass are highly effective in the treatment of GCTs with five-year survival rate of more than 95%. [3] As a result, the number of GCT survivors with long life expectancy is rising. Therefore, maintaining patients' quality of life and minimizing treatment-related morbidity and mortality has gained more significant interest in recent years.
Venous thromboembolism (VTE) commonly occurs in cancer patients. [4] It affects about 10% of patients with malignancy. The pathophysiology is thought to be multifactorial and is related to the type of tumor, anatomic location, patient's comorbidities, type of treatment, etc. [5] When compared to patients with different type of malignancy, GCT patients have higher incidence of VTE events. [6] VTE is associated with increased morbidity and mortality in cancer patients. Levitan et al found more than a threefold higher risk of recurrent VTE and death in cancer patients compared to patients with VTE without cancer diagnosis. [7] Incidence of VTE in GCT patients has been assessed in a few studies and the results vary widely.
Honecker et al observed 9% VTE incidence in patients before starting chemotherapy, while there was only a 2% incidence of VTE during first-line chemotherapy. [8] In a different study, Piketty et al found a 14% incidence of VTE during first-line chemotherapy and 5% incidence of VTE after chemotherapy. [6] Several groups focused on identification of risk factors of VTE events in GCT patients. [6,[9][10][11][12] Weijl et al observed an increased risk of VTE in patients with liver metastases (odds ratio = 4.9). [10] Piketty et al identified body surface area > 1.9m 2 (relative risk (RR) = 5, 95% confidence interval (CI) 1.8-13.9) and elevated serum lactate dehydrogenase (RR = 6.4, 95% CI 2.3-18.2) as independent risk factors. In their study, patients without any risk factors had 4% probability of having VTE, while patients with at least 1 risk factor had 26% probability of having VTE. [6] Prophylactic anticoagulation has been shown to decrease the risk of symptomatic VTE in cancer patients. (RR = 0.56, 95% CI 0.47-0.68) [13] Gizzi et al studied the incidence of thromboembolic events in GCT patients treated with first-line chemotherapy and observed lower incidence of thromboembolic events in patients receiving thromboprophylaxis when compared to patients without prophylaxis. [12] However, small number of patients in each subgroup of this study makes the interpretation of the results difficult and larger study is needed to elucidate the relationship between thromboprophylaxis and incidence of VTE in GCT patients undergoing cisplatin-based chemotherapy.
The aim of this retrospective study was to evaluate the effect of low molecular weight heparin (LMWH) prophylaxis on incidence of VTE events and outcome in germ cell tumor patients treated with first-line chemotherapy.

Study patients
This retrospective study was conducted using the National Cancer Institute medical records database.
The study was approved by the Institutional Review Board and waiver of consent form was granted.
Patients diagnosed with germ cell tumors treated with first line/adjuvant chemotherapy at the National Cancer Institute, Bratislava, Slovakia from January 2000 to December 2017 were eligible.
Patients with any concurrent malignancy, other than non-melanoma skin cancer in the previous 5 years were excluded from the study. Excluded were also patients with previous chemotherapy, patients with venous thromboembolism diagnosed on the initial staging exam and patients on anticoagulation therapy (therapeutic or prophylactic) started before the initiation of first line chemotherapy.

Definition of VTE event
VTE event was defined as any venous thrombosis or pulmonary embolism occurring between Day 1 of first cycle of the first-line chemotherapy and Day 21 of the last cycle of the first-line chemotherapy.
Cases of superficial phlebitis were not classified as events. Every VTE event had to be confirmed by imaging studies, either Doppler ultrasonography or a CT scan. Depending on patients' presenting symptoms, the events were divided into symptomatic and incidental, if discovered on imaging done for a different purpose.

Baseline data
During the initial staging, patients had a CT scan of the chest, abdomen and pelvis. Baseline data regarding age, primary tumor location, tumor histology, TNM stage, International Germ Cell Cancer Collaborative Group (IGCCCG) risk class and first-line chemotherapy regimen were recorded. Blood coagulation tests were not routinely performed during the initial screening.

VTE prophylaxis
LMWH prophylaxis was not routinely prescribed before January 2010 during hospitalization. At our institution, all GCT patients are hospitalized during chemotherapy. In December 2007, American Society of Clinical Oncology released clinical practice guidelines recommending prophylactic anticoagulation for hospitalized patients receiving chemotherapy. [14] Therefore, starting in January 2010, we progressively implemented prophylactic anticoagulation with low molecular heparin (nadroparin 0,4 ml or equivalent). However, not all physicians integrated this guideline into their practice and LMWH prophylaxis was prescribed at the individual physician's discretion.

STATISTICAL ANALYSIS
We performed a retrospective review of patients' medical records. All thromboses or pulmonary embolism, confirmed by imaging modality, were classified as events. Patients' characteristics were tabulated and summarized as the median (range) values for continuous variables and frequency (percentage) for categorical variables, respectively. Fisher's exact test was used for statistical analysis to compare VTE events between groups with and without prophylaxis.
Primary outcome was the overall incidence of VTE events occurring between Day 1 of first cycle of the first-line chemotherapy and Day 21 of the last cycle of the first-line chemotherapy. Secondary outcomes were incidences of VTE events in various subgroups and overall survival.
Time to VTE was calculated from the start date of chemotherapy to date of VTE diagnosis. Log-rank test was used to compare the differences between time to VTE between patients with and without prophylaxis.
Median follow-up was calculated as median time of observation of study patients. Overall survival was calculated from the start date of chemotherapy to date of the last follow-up or death of the patient.
Kaplan-Meier method was used to estimate overall survival. The log-rank test was used to compare differences in survival between patients with and without prophylaxis. All calculations were done in NCSS 2019 statistical software. [15] Results

Patients' characteristics
Our cohort included 353 chemotherapy naive patients with GCTs treated with first line chemotherapy (Flow diagram). Patients' characteristics are summarized in Table 1. Median age of patients at time of enrollment was 32 years (ranging from 17 to 63 years). The majority of patients (75.9%) had nonseminomatous germ cell tumor. All patients received platinum-based chemotherapy.   Table 2.   Table S1).

Association between VTE prophylaxis and patients/tumor characteristics
There were 12 VTE events in patients with non-seminomatous germ cell tumors (NSGCTs) and 2 events occurred in patients with seminoma. There were no statistically significant differences in VTE incidence between patients with and without prophylaxis based on tumor histology. year overall survival of the study group was 87.99% (95% CI 84.49% -91.49%) and 84.27% (95% CI 80.22% -88.31%), respectively. There was no difference in overall survival in patients with or without prophylaxis (HR = 0.61, 95% CI 0.32-1.13; P = 0.0784) (Fig. 1). The results are summarized in Table 3.
Patients with extragonadal GCT and patients with NSGCT histology receiving VTE prophylaxis had significantly shorter survival compared to patients without prophylaxis (HR = 0.29, 95% CI 0.08-1.12; P = 0.0373, HR = 0.50, 95% CI 0.25-0.99; P = 0.0179 respectively) ( Fig. 2A and 2B). We have also observed a trend to shorter overall survival in patients receiving prophylaxis with chemotherapy regimen other than BEP (HR = 0.50, 95% CI 0.22-1.12; P = 0.0614). We analyzed the incidence of treatment related deaths (TRD) in patients with primary extragonadal tumors and NSGCT histology based on LMWH prophylaxis. Treatment related death was defined as death during first-line chemotherapy. Patients with extragonadal tumors receiving LMWH prophylaxis had a higher incidence of TRD compared to patients without prophylaxis (21.4% vs. 0.0%, P = 0.0556). Patients with NSGCT histology on LMWH prophylaxis also had a higher incidence of TRD compared to patients without prophylaxis. (10.9% vs. 3.9%, P = 0.0552). On subgroup analysis of patients with NSGCT histology we found that this trend was driven by TRD of patients with primary extragonadal tumors.

Incidence of major bleeding during the VTE prophylaxis
In our cohort, there were 13 patients, who suffered major bleeding (grade 3-5). There were 7 patients (2.8%) received no prophylaxis and 6 patients (5.8%) received LMWH prophylaxis. The difference was not statistically significant (P = 0.22)

Discussion
In the present study, we examined the relationship between prophylactic anticoagulation during chemotherapy and incidence of VTE events as well as the association between prophylactic anticoagulation and overall survival of GCT patients treated with first line chemotherapy. In order to assess the effect of prophylactic anticoagulation on the incidence of VTE events, we included only events occurring during first-line chemotherapy, when patients were also receiving LMWH prophylaxis.
We have observed that most VTE events occur even before the initiation of chemotherapy. There was a 4% incidence of VTE events occurring during chemotherapy. Observed incidence of VTE events is in line with the incidences reported in the literature. [6,8,10,[17][18][19] However, there is a wide variation in the reported incidences. While the lowest reported incidence is 2%, in a different study, there was 23.7% incidence of thromboembolic events. [8,19] A significant part of this variation is probably caused by different inclusion criteria: including arterial events, including patients with VTE events before the start of chemotherapy, and events occurring several months after chemotherapy. Small number of patients some studies may also contribute to this variability.
We have observed no significant differences in VTE incidence between patients with and without LMWH prophylaxis. While there have been several studies assessing VTE incidence and identifying VTE risk factors in GCT patients, most of them included only a small number of the study patients with LMWH prophylaxis. Solari et al. compared the incidence of thromboembolic events in patients receiving limited and extended LMWH prophylaxis. Limited prophylaxis was administered only during hospitalization. Extended prophylaxis was administered daily from the first day of the first cycle to day 21 of the last cycle of chemotherapy. They did not observe significant differences between these two groups. However, their study did not include a control group with no prophylaxis and therefore the effect of LMWH prophylaxis cannot be assessed. Paradoxically, the incidence of thromboembolic events reported in their study (23.7%) was much higher than in other studies. [19] However, arterial events were also included in their analysis. Gizzi et al also compared the VTE incidence in GCT patients with and without LMWH prophylaxis. In their study, prophylaxis was administered to a subgroup of patients with risk factors for VTE (elevated lactate dehydrogenase or high body surface area). They have observed no statistically significant difference in VTE incidence between the two groups. However, neither the type of LMWH used nor the dosing of prophylaxis are mentioned. [12] Unexpectedly, there was a trend to shorter overall survival in our patients who received LMWH prophylaxis. On further analysis we found a significantly shorter overall survival in patients receiving LMWH prophylaxis with NSGCT histology or extragonadal tumor location.
Prospective study assessing the effect of prophylactic anticoagulation in patients with GCT receiving chemotherapy compared to no prophylaxis is lacking. However, the data available suggest that LMWH prophylaxis does not offer the expected benefits in terms of decreased incidence of VTE events in GCT patients. [12,19] On the contrary, our data suggest that administering LMWH prophylaxis might To the best of our knowledge, this is the largest study evaluating the effect of LMWH prophylaxis on VTE incidence in GCT patients receiving chemotherapy. Our study has several limitations. First of all, LMWH prophylaxis was not random, possibly causing selection bias. It is possible that patients at higher risk for VTE were given thromboprophylaxis more frequently what could in turn obscure the effect of thromboprophylaxis. However, incidence of VTE in patients without prophylaxis before 2010 was similar to incidence of VTE in subgroup of patients with prophylaxis after 2010, totally as well as in subgroup analysis based on IGCCCG risk group (Supplementary Table S1). This support the conclusion of no beneficial effect of prophylaxis in GCTs patients. Secondly, the study has retrospective design. Some VTE events could have been missed as a result of incomplete medical records.

Conclusion
In conclusion in this large retrospective analysis, we showed that LMWH prophylaxis was not associated with decreased VTE incidence. Moreover, there was a higher incidence of treatment related deaths in patients with extragonadal tumor location. Taking into account these data, LMWH prophylaxis during hospitalization should not be used in GCT patients receiving chemotherapy.

Ethics approval
The Institutional Review Board of the National Cancer Institute, Bratislava, Slovakia approved this study and granted a waiver of consent form for the collection, analysis and publication of the retrospectively obtained and anonymised data for this non-interventional study.
Not applicable.