Risk Factors, Treatment and Prognosis of Patients with Lung Cancer after Heart Transplantation

Long-term survival after heart transplantation (HTX) is impacted by adverse effects of immunosuppressive pharmacotherapy, and post-transplant lung cancer is a common occurrence. This study aimed to examine the risk factors, treatment, and prognosis of patients with post-transplant lung cancer. We included 625 adult patients who received HTX at Heidelberg Heart Center between 1989 and 2018. Patients were stratified by diagnosis and staging of lung cancer after HTX. Analysis comprised donor and recipient characteristics, medications including immunosuppressive drugs, and survival after diagnosis of lung cancer. A total of 41 patients (6.6%) were diagnosed with lung cancer after HTX, 13 patients received curative care and 28 patients had palliative care. Mean time from HTX until diagnosis of lung cancer was 8.6 ± 4.0 years and 1.8 ± 2.7 years from diagnosis of lung cancer until last follow-up. Twenty-four patients (58.5%) were switched to an mTOR-inhibitor after diagnosis of lung cancer. Multivariate analysis showed recipient age (HR: 1.05; CI: 1.01–1.10; p = 0.02), COPD (HR: 3.72; CI: 1.88–7.37; p < 0.01), and history of smoking (HR: 20.39; CI: 2.73–152.13; p < 0.01) as risk factors for post-transplant lung cancer. Patients in stages I and II had a significantly better 1-year (100.0% versus 3.6%), 2-year (69.2% versus 0.0%), and 5-year survival (53.8% versus 0.0%) than patients in stages III and IV (p < 0.01). Given the poor prognosis of late-stage post-transplant lung cancer, routine reassessment of current smoking status, providing smoking cessation support, and intensified lung cancer screening in high-risk HTX recipients are advisable.


Introduction
Heart transplantation (HTX) remains the standard of care for patients with irreversible end-stage heart failure [1,2]. Over the last decades, post-transplant survival has continuously been improving due to advances in surgical management, clinical experience, and immunosuppressive drug therapy [3][4][5][6]. The focus of post-transplant care has consequently been shifting from early risks such as acute rejection or surgical complications (bleeding, thromboembolic events, and wound infections) towards late sequelae such as cardiac allograft vasculopathy or neoplasms [7][8][9].
As a consequence of the elevated cardiovascular risk profile, many HTX recipients are at high risk for post-transplant lung cancer. However, post-transplant lung cancer is still poorly characterized among HTX recipients. The relative importance of risk factors, the role of the underlying immunosuppressive drug therapy, and the clinical course of patients with post-transplant lung cancer are barely understood. We therefore sought to investigate the risk factors, treatment, and prognosis of patients with lung cancer after HTX. Special emphasis was put on the clinical presentation of patients with lung cancer after HTX including location, classification, histology, and staging of lung cancer after HTX as well as the possible influence of post-transplant drug regimens, including immunosuppressive agents.

Patients
This study was performed in accordance with the ethical standards of the Declaration of Helsinki. Approval was granted by the institutional review board (IRB) of Heidelberg University (ethics approval number: S-286/2015, Version 1.2, 28 July 2020). We obtained written informed consent from patients for their inclusion in the Heidelberg HTX Registry and the clinical and scientific use of their data. The ethics approval does not require additional consent for this observational study as only routine clinical data were used [30][31][32][33][34][35][36][37].
All adult patients (≥18 years) who received HTX at Heidelberg Heart Center, Heidelberg, Germany, between 1989 and 2018 were included in this study, except for patients who had undergone HTX more than once. Minimum follow-up data of two years after HTX was obtained from all patients (data available until 1 January 2021). We initially stratified patients by diagnosis of lung cancer after HTX: patients with diagnosed lung cancer after HTX ("lung cancer group") and patients without diagnosed lung cancer after HTX ("no lung cancer group"). Patients in the lung cancer group were further subdivided by stage (I-IV) according to the 8th edition of the Union for International Cancer Control (UICC 8) [38].

Follow-Up
Patient follow-up was performed according to Heidelberg Heart Center's routine clinical protocol. After the initial hospital stay following surgery, patients were seen as outpatients in the HTX clinic monthly during the first six months after HTX, then bimonthly until the end of the first year, and approximately three to four times per year thereafter (with additional visits when clinically required) [30][31][32][33][34][35][36][37].

Post-Transplant Medication
Post-transplant medication including immunosuppressive drug therapy was administered as per the center's usual standard of care. Perioperatively, patients received an anti-thymocyte globulin-based immunosuppression induction therapy. Cyclosporine A and azathioprine were used as the initial immunosuppressive regimen prior to 2001. From 2001, mycophenolate mofetil replaced azathioprine subsequently and tacrolimus replaced cyclosporine A from 2006 onward. Steroids were tapered incrementally during the initial post-transplant months and were discontinued six months after HTX (unless clinically needed) [30][31][32][33][34][35][36][37].
We used univariate analyses to search for intergroup differences including recipient data, previous open-heart surgery, principal diagnosis for HTX, donor data, transplant sex mismatch, perioperative data, post-transplant drug regimen, and immunosuppressive drug therapy. Patients with lung cancer after HTX were further analyzed with regard to signs and symptoms of lung cancer after HTX. Characterization also included lung cancer location, classification, histology, staging, and treatment modalities. Our analysis of risk factors for lung cancer after HTX included a multivariate analysis (Cox regression model) with the following five clinically relevant parameters based on a predetermined model: recipient age (years), recipient coronary artery disease (in total), recipient peripheral artery disease (in total), recipient chronic obstructive pulmonary disease (in total), and recipient history of smoking (in total). We did not include additional parameters in this multivariate analysis of risk factors for lung cancer after HTX in order to avoid biased regression coefficients and to ensure a stable number of events (patients with diagnosis of post-transplant lung cancer) per analyzed variable [30][31][32][33][34][35][36][37].
The primary outcome of this study was mortality after diagnosis of post-transplant lung cancer in patients after HTX. Secondary outcomes included analysis of risks factors and treatment of post-transplant lung cancer in patients after HTX.

Baseline Characteristics and Medication after Heart Transplantation
Of 625 included HTX recipients, 41 patients (6.6%) were diagnosed with post-transplant lung cancer while 584 patients (93.4%) were not diagnosed with lung cancer during the study period. The mean interval from HTX to initial diagnosis of post-transplant lung cancer was 8.6 ± 4.0 years and 1.8 ± 2.7 years from diagnosis of lung cancer until last follow-up.
Patients with lung cancer after HTX had a significantly higher recipient age (55. 4  12.0 ± 14.4 py, difference: 8.2 py, 95% CI: 4.7-11.7 py, p < 0.01). We found no statistically significant differences between both groups with regard to the remaining recipient data, previous open-heart surgery, principal diagnosis for HTX, donor data, transplant sex mis-match, or perioperative data (all p ≥ 0.05). Baseline characteristics of study participants are summarized in Table 1.
Analysis of the immunosuppressive drug regimen showed no statistically significant difference between patients with and without lung cancer after HTX with regard to the use of cyclosporine A, tacrolimus, azathioprine, or mycophenolate mofetil (all p ≥ 0.05). As azathioprine is known to be the immunosuppressant with the highest impact on cancer, we compared lung cancer patients with or without azathioprine with regard to the percentage of lower (stages I and II) and higher stages (stages III and IV) of post-transplant lung cancer. There was no statistically significant difference between lung cancer patients with or without azathioprine regarding lower (azathioprine: 7 of 23 [30.4%]  We also did not observe statistically significant differences between patients with and without lung cancer after HTX correlating with the initial blood concentration of cyclosporine A or tacrolimus as the target drug trough blood levels of calcineurin inhibitors changed over time and were higher in the past. In terms of concomitant medications, we observed no statistically significant differences between patients with and without lung cancer after HTX with respect to the administration of acetylsalicylic acid, beta-blockers, ivabradine, calcium channel blockers, angiotensin-converting-enzyme inhibitors/angiotensin II receptor blockers, or statins (all p ≥ 0.05). An overview of medications after HTX is given in Table 2.

Clinical Presentation of Patients with Lung Cancer after Heart Transplantation
In 26 of 41 patients (63.4%) with lung cancer after HTX, the diagnosis was made after the occurrence of at least one of the following symptoms: shortness of breath Regarding smoking status, 40 of 41 patients (97.6%) diagnosed with lung cancer after HTX had a history of smoking before HTX. In order to be listed for HTX, patients had to quit smoking and had to be tobacco product free for a minimum of six months. After HTX, 35 of 41 patients (85.4%) who developed post-transplant lung cancer had started smoking again. Clinical presentation of patients with lung cancer after HTX is shown in Table 3. Abbreviations: CABG = coronary artery bypass graft; CI = confidence interval; CMP = cardiomyopathy; COPD = chronic obstructive pulmonary disease; f = female; eGFR = estimated glomerular filtration rate; HTX = heart transplantation; m = male; n = number; py = pack year; SD = standard deviation; VAD = ventricular assist device; † = presence of coronary artery disease before HTX;ˆ= eGFR < 60 mL/min/1.73 m 2 ; • = congenital, valvular or ventricular surgery; * = statistically significant (p < 0.05). Abbreviations: ASA = acetylsalicylic acid; ACE inhibitor = angiotensin-converting-enzyme inhibitor; ARB = angiotensin II receptor blocker; CI = confidence interval; HTX = heart transplantation; n = number; n. a. = not applicable; † = gastric protection defined as proton pump inhibitor (PPI) or histamine receptor (H2) blocker.   [16.7%]). In addition, four patients (4 of 41 [9.8%]) were already on everolimus before diagnosis of post-transplant lung cancer as they showed loss of kidney function under calcineurin inhibitors. Prognosis and treatment of patients with lung cancer after HTX is presented in Table 5.

Multivariate Analysis of Risk Factors for Lung Cancer after Heart Transplantation
In order to assess the impact of different variables on lung cancer after HTX, we performed a multivariate analysis of risk factors for lung cancer after HTX. Out of five analyzed variables, the following three were significantly associated with the occurrence of lung cancer after HTX: higher recipient age (HR: 1.05, CI: 1.01-1.10; p = 0.02), chronic obstructive pulmonary disease (HR: 3.72, CI: 1.88-7.37; p < 0.01), and history of smoking (HR: 20.39, CI: 2.73-152.13; p < 0.01). Coronary artery disease (HR: 1.26, CI: 0.64-2.49; p = 0.50) and peripheral artery disease (HR: 0.75, CI: 0.36-1.57; p = 0.45) were not statistically significant. Multivariate analysis of risk factors for lung cancer after heart HTX is shown in Table 6.

Survival after Post-Transplant Lunger Cancer
Patients with lung cancer after HTX generally had a poor prognosis. Overall

Frequency and Significance of Lung Cancer after Heart Transplantation
Post-transplant lung cancer is the most common solid organ malignancy after HTX and plays an important role in the long-term care of HTX recipients [25][26][27][28][29]. Nevertheless, the field lacks sufficient data on the underlying risk factors, the available treatment options, and the clinical prognosis of patients with lung cancer after HTX. Given this need, we performed this large study with a total of 625 HTX recipients to characterize patients with post-transplant lung cancer in detail. Forty-one patients (6.6%) were diagnosed with post-transplant lung cancer and mean time from HTX until diagnosis of lung cancer was 8.6 ± 4.0 years.
Previous studies published post-transplant lung cancer rates ranging from 1.6% to 5.8% [18][19][20][21][22][23][24]26,28,39]. These numbers clearly highlight the increased risk for the development of lung cancer in patients after HTX compared to other solid-organ transplant recipients and the general population [18,19,23,26,28]. Earlier studies have differed in length of post-transplant follow-up and consequently in time between HTX and the diagnosis of cancer, which may have caused an underestimation of posttransplant lung cancer rates. Pham and colleagues [23] reported a post-transplant lung cancer rate of 1.6% (10 of 608) with a mean interval from HTX to lung cancer detection of 2.3 ± 1.5 years, whereas in our study, we observed a higher post-transplant lung cancer rate of 6.6% (41 of 625) with a longer mean interval from HTX to lung cancer detection of 8.6 ± 4.0 years.
Furthermore, in some studies, post-transplant lung cancer was already diagnosed within the first year after HTX [18,[20][21][22]. Given the rather slow growth rate of lung cancer, these tumors were likely to preexist before HTX [20]. In contrast, no patient was diagnosed with post-transplant lung cancer within 24 months after HTX in our study,

Frequency and Significance of Lung Cancer after Heart Transplantation
Post-transplant lung cancer is the most common solid organ malignancy after HTX and plays an important role in the long-term care of HTX recipients [25][26][27][28][29]. Nevertheless, the field lacks sufficient data on the underlying risk factors, the available treatment options, and the clinical prognosis of patients with lung cancer after HTX. Given this need, we performed this large study with a total of 625 HTX recipients to characterize patients with post-transplant lung cancer in detail. Forty-one patients (6.6%) were diagnosed with post-transplant lung cancer and mean time from HTX until diagnosis of lung cancer was 8.6 ± 4.0 years.
Previous studies published post-transplant lung cancer rates ranging from 1.6% to 5.8% [18][19][20][21][22][23][24]26,28,39]. These numbers clearly highlight the increased risk for the development of lung cancer in patients after HTX compared to other solid-organ transplant recipients and the general population [18,19,23,26,28]. Earlier studies have differed in length of post-transplant follow-up and consequently in time between HTX and the diagnosis of cancer, which may have caused an underestimation of post-transplant lung cancer rates. Pham and colleagues [23] reported a post-transplant lung cancer rate of 1.6% (10 of 608) with a mean interval from HTX to lung cancer detection of 2.3 ± 1.5 years, whereas in our study, we observed a higher post-transplant lung cancer rate of 6.6% (41 of 625) with a longer mean interval from HTX to lung cancer detection of 8.6 ± 4.0 years.
Furthermore, in some studies, post-transplant lung cancer was already diagnosed within the first year after HTX [18,[20][21][22]. Given the rather slow growth rate of lung cancer, these tumors were likely to preexist before HTX [20]. In contrast, no patient was diagnosed with post-transplant lung cancer within 24 months after HTX in our study, which might be the result of extensive pre-transplant screening for lung cancer including the presence of B symptoms, smoking behavior, medical history, physical examination, and chest X-ray/computed tomography. Considering the above-mentioned frequencies and intervals to diagnosis, post-transplant lung cancer is a long-term HTX sequela of considerable importance.

Risk Factors for Lung Cancer after Heart Transplantation
As HTX recipients generally require a higher-dosed immunosuppressive drug regimen than other solid organ transplant recipients to prevent rejection, they seem to have an elevated risk to develop neoplasms [18][19][20][21][22][23][24][25][26][27][28][29]. Calcineurin inhibitors (cyclosporine A or tacrolimus)-which are commonly used as standard immunosuppressants in HTX recipients-in particular are associated with an increased rate of neoplasms and can also promote tumor progression via direct cellular effects [20,[40][41][42]. However, we did not observe a statistically significant difference regarding the use of cyclosporine A or tacrolimus between HTX recipients with or without post-transplant lung cancer. This may indicate that immunosuppressive drug therapy itself does not necessarily cause a higher occurrence of post-transplant lung cancer but rather enhances preexisting risk factors [18,22]. HTX recipients are a selected group of patients with an elevated risk profile including higher age, male sex, history of smoking, chronic obstructive pulmonary disease, and ischemic cardiomyopathy [18][19][20][21][22][23][24]30].
Of the discussed factors, smoking appears to be by far the most important risk factor for lung cancer after HTX [18][19][20][21][22][23][24]. Furthermore, smoking may potentiate the adverse effects of the underlying immunosuppressive drug therapy, especially in patients who restarted smoking after HTX. In our study, 40 of 41 patients with lung cancer after HTX smoked before HTX (97.6%) and 35 of these 41 patients started smoking again after HTX (85.4%). We therefore strongly recommend asking patients about their smoking status before and after HTX as well as providing assistance and guidance to those patients who started smoking again in order to ensure a permanent cessation of smoking.

Clinical Outcomes of Patients with Lung Cancer after Heart Transplantation
The overall survival of HTX recipients with post-transplant lung cancer is mostly quite poor [18,19,21,23,24,27,28]. We observed an overall 1-year survival rate of HTX recipients of 34.1% (14 of 41), an overall 2-year survival rate of 22.0% (9 of 41), and an overall 5-year survival rate of 17.1% (7 of 41) after diagnosis of post-transplant lung cancer. This is in line with findings by Pham and colleagues [23] who found an overall 2-year survival rate of 22.0%, and by Crespo-Leiro and colleagues [19] who reported an overall 5-year survival rate of 16.0%. A possible explanation for these low survival rates could be the fact that many HTX recipients are diagnosed at an advanced stage of disease [18][19][20][21][22][23][24].
When stratified by stage according to UICC 8, patients in stages I and II lung cancer after HTX showed a significantly better 1-year (100.0% versus 3.6%), 2-year (69.2% versus 0.0%), and 5-year survival (53.8% versus 0.0%) than patients in stages III and IV in our study. Similar findings were published by Crespo-Leiro and colleagues [19] who found a superior 2-year survival (70.0% versus 16.0%) in patients with curative surgery, by Bruschi and colleagues [18] who reported a significantly better 5-year survival (56.0% versus 0.0%) in patients with early-stage lung cancer after HTX, and by Bagan and colleagues [27] who showed a significantly better 5-year survival (44.0% versus 0.0%) in patients with N0 stage.
These data indicate that a 5-year survival after diagnosis of post-transplant lung cancer of about 50% can be achieved in HTX recipients if the following three criteria are fulfilled [18][19][20]23,27]: First, lung cancer after HTX is detected at an early stage (preferably stages I and II). Second, cura-tive treatment (especially surgery) is feasible as surgical resection is the treatment of choice for lung cancer. Third, prompt and aggressive treatment of lung cancer is initiated in order to prevent lymph node involvement and metastases [18][19][20]23,27].
Whereas criteria two and three strongly depend on the patient's health status and underlying comorbidities, the first criterion may be improved by intensified lung cancer screening as patients are often asymptomatic at the time of lung cancer detection [18][19][20][21][22]. Standard lung cancer screening in HTX recipients mainly consists of annual chest Xrays, however, the sensitivity of this method to detect early-stage lung cancer is rather low [19,22,27]. In addition, if an abnormality is found on chest X-ray, it is often misinterpreted as an infectious process rather than a cancerous process [21]. Low-dose chest computed tomography shows promising results as an additional screening modality for the early detection of post-transplant lung cancer [18][19][20][21][22]27]. Therefore, high-risk HTX recipients (higher age, male sex, history of smoking, chronic obstructive pulmonary disease, and ischemic cardiomyopathy) may benefit from an intensified lung cancer screening including low-dose chest computed tomography.

Study Limitations
The results of this study were based on a single-center registry (Heidelberg HTX Registry) including the highly detailed data of 625 HTX recipients who received HTX at Heidelberg Heart Center. As this study design has certain limitations, our findings should be interpreted with caution and within the context of the existing literature. Nevertheless, we would like to emphasize that our study was comparable to multicenter studies in sample size and our patients received standardized treatment and follow-up, lowering the likelihood of potential confounders and selection bias [14,[30][31][32][33][34][35][36][37].
Considering the slow growth of these tumors, long-term follow-up is essential to detect lung cancer after HTX. We therefore decided to include adult HTX recipients who received HTX at Heidelberg Heart Center between 1989 and 2018, ensuring a minimum follow-up of two years after HTX. Given the long study period, a possible era effect as a result of changes in medical and surgical care may have affected our findings. As tacrolimus replaced cyclosporine A as the main immunosuppressive agent from 2006 onward, the maximum possible follow-up time of patients with tacrolimus was shorter than of patients with cyclosporine A. However, both groups had a mean follow-up time of more than five years after HTX, supporting the robustness of our results [14,[30][31][32][33][34][35][36][37].
Our findings should be seen as hypothesis-generating, particularly in the context of risk factors for post-transplant lung cancer and mortality after HTX as multiple factors can influence these outcomes. Large multi-center trials are required to confirm our findings.

Conclusions
Many HTX recipients have a distinct cardiovascular risk profile with an elevated risk for post-transplant lung cancer. Specifically, higher recipient age, chronic obstructive pulmonary disease, and history of smoking are significant risk factors for lung cancer after HTX. Notably, 35 of 41 patients (85.4%) who developed post-transplant lung cancer in this study had started smoking again after HTX. Given the particular risk for patients who take up smoking again after HTX, it is advisable to intensify efforts to ensure continued abstinence. This should begin with reassessment of smoking status at every follow-up encounter after HTX as well as offering guidance and assistance with smoking cessation if needed.
We observed an enormous difference in survival between patients diagnosed in an early stage of lung cancer after HTX and those diagnosed later. Patients with early-stage lung cancer after HTX showed a 5-year survival rate of more than fifty percent after diagnosis of post-transplant lung cancer, which is comparable to non-transplant patients with early-stage lung cancer [43], while patients with late-stage lung cancer after HTX had a very poor prognosis. The dramatically differing survival strongly suggests that early diagnosis is key. Thorough screening for lung cancer should start prior to HTX and continue regularly afterward. In addition to annual chest X-rays, low-dose chest computed tomography in high-risk HTX recipients may be a viable option to intensify screening efforts. However, comprehensive data on this are currently lacking and further research is needed before changing clinical practice.

Informed Consent Statement:
We obtained written informed consent from patients for their inclusion in the Heidelberg HTX Registry and the clinical and scientific use of their data. The ethics approval does not require additional consent for this observational study as only routine clinical data were used. Data Availability Statement: Not applicable.