Cancer stage at diagnosis is presented in Figure 2. Transplant patients were diagnosed at earlier stages of RCC. Cancer stage distributions were similar between transplant recipients and general population for colon cancer. NSCLC, breast cancer, prostate cancer, bladder cancer, and malignant melanoma were diagnosed at more advanced stages in transplant recipients.
Treatment data are presented in Table 1. For each tumor type, the proportions of patients receiving immunosuppression reduction or discontinuation were low. It is possible that these low numbers may represent a substantial degree of underreporting. As expected, for all cancer types, surgery was the most common treatment modality for localized stage I and II and most stage III cancers. Some differences in treatment were noted between the transplant and SEER populations, particularly with respect to radiation therapy, however, the absolute magnitude of differences were often small. In general, although statistically significant differences were noted between transplant and SEER populations with respect to therapies, the approach to treating most stages for each cancer were similar.
Stage-specific and disease-specific survival data are presented in Figure 3. For most stages for each tumor type, disease-specific survival by Kaplan-Meier was lower in transplant patients. Cox proportional hazards analysis of factors that influence disease-specific survival are presented in Figure 4. For each cancer, the two factors that had the greatest negative effect on survival were stage at diagnosis and transplantation. Prostate and bladder cancer demonstrated a greater effect of transplantation than cancer stage, whereas all other tumor types studied demonstrated a greater effect of stage at diagnosis. Surgery was observed to extent a positive effect on survival.
The overall evidence in this study supports the concept that cancers arising in transplant recipients are associated with worse outcomes and an apparent increase in biologic aggressiveness. Cancers arise in transplant recipients’ surprisingly early after transplantation, ranging from a median of 39 (NSCLC) to 77 months (RCC). Expressed differently, among the seven cancers studied, the longest median time from transplant to cancer diagnosis was observed with RCC; however, even this time (6 years and 5 months) is impressively short. These observations indicate that transplant recipients experience the greatest risk of developing (most) cancer(s) within the first 6 years after transplantation. A substantial proportion of cancer risk in transplant recipients is, therefore, incurred after a relatively brief period of immunosuppression. It is possible that the early appearance of cancer in the posttransplant period may result from the more intense immunosuppression, and raises the possibility that cancer risk may decline as immunosuppression is reduced over time.
Evaluation of patients at all ages for age at cancer diagnosis demonstrated that transplant patients are diagnosed at an earlier age than in the general population. This observation may have occurred because patients older than 60 years are not infrequently excluded as transplant candidates, thereby inducing an age limitation on the transplant population. When the analysis was restricted to patients younger than 60 years at the time of cancer diagnosis, all cancers studied (except RCC) showed almost identical age distributions for age at cancer diagnosis in the transplant and general populations.
Analysis of the extent of cancer spread at the time of diagnosis was of particular importance as it was the primary measure by which a possible effect of immunosuppression on cancer behavior could be assessed. These analyses demonstrated that several cancers (breast cancer, bladder cancer, and malignant melanoma) were diagnosed at a higher stage in transplant recipients. The increase in cancer stage at diagnosis for malignant melanoma was surprising, as it occurred despite a widespread recognition of the need for enhanced screening for skin cancers in transplant recipients. In addition, these observations for other cancers occurred despite the greater degree of physician contact generally given to transplant patients. These data argue strongly for increasing education of physicians and transplant recipients regarding cancer screening. Of interest, only a single cancer, RCC, was associated with a shift toward earlier cancer stage at diagnosis. A potential explanation for this observation may be the increased exposure of renal failure patients and transplant recipients to abdominal imaging studies (CT scan, magnetic resonance imaging, and ultrasound). In addition, end stage kidneys with renal cystic lesions are at increased cancer risk.
Stage-stratified, disease-specific survival was worse in transplant recipients for one or more stages in several cancers including: colon cancer (all stages), NSCLC (stage II), breast cancer (stage III), prostate cancer (stage II, III, and IV), bladder cancer (stage III), and RCC (stage IV). Stage-stratified, disease-specific survival in other stages for the cancers studied was often numerically lower for transplant recipients, but did not reach statistical significance. This may have been due to the relatively small numbers of subjects analyzed for each cancer stage.
Disease-specific survival was further analyzed by Cox proportional hazards modeling of several risk factors for survival (age, gender, cancer stage at diagnosis, surgical therapy, and transplantation). Not surprisingly, surgical therapy was a significantly positive factor that favored survival, because surgery was likely performed for early stage cancers. A significant negative effect of transplantation was observed on disease-specific survival for each cancer, which suggests a substantive effect of immunosuppression or comorbidities or both. Surprisingly, the magnitude of the negative effect of transplant status was relatively comparable to cancer stage at diagnosis, and for prostate and bladder cancer, the effect of transplantation was greater than the effect of cancer stage at diagnosis.
Why does transplantation confer such a poor prognosis for cancer outcomes? Is it that immunosuppressive therapy alters the host-tumor relationship resulting in increased biologic aggressiveness, or does the presence of increased comorbidities and reduced physical condition in transplant recipients also play a role? Functional status data could control for differences in physical condition, however, both SEER and IPITTR registries contain little functional status data. The observation of more advanced cancer stage at diagnosis in transplant recipients argues for a real effect of immunosuppressive therapy, particularly because transplant patients generally have more physician contact than the general population. This question is important, because if immunosuppressive therapy does result in increased biologic aggressiveness of cancers, immunosuppression reduction should be evaluated for its potential to improve outcomes in transplant recipients.
Several considerations were involved in the selection of individual cancers for study. From a practical perspective, the study was limited primarily by the smaller transplant population, particularly with respect to cancer stage-specific analyses. Therefore, to assure adequate numbers of patients, more commonly occurring cancers were selected for analysis. In addition, previous cancer immunotherapy studies in patients with RCC or malignant melanoma have demonstrated these cancers to be immunosensitive. The possibilities that immunosuppressive effects may be magnified in these two populations were additional considerations for their selection for study.
Differences in cancer treatment and immunosuppressive factors may influence observations when comparing transplant and general population data. For example, chemotherapy, either myelosuppressive or myeloablative, induces transient and possible longer term immunosuppression. Myeloablative chemotherapy, may cause results in the general population to resemble those in a systemically immunosuppressed population. Unfortunately, minimal chemotherapy data were available in the SEER database and were inadequate for meaningful analysis. Similarly, hormonal therapy data were also inadequate.
Transplant practitioners reduce or discontinue immunosuppression after cancer diagnosis in transplant recipients. When immunosuppression is reduced, the observed effect of immunosuppression may be diminished, thereby resulting in an underestimation of the effect of immunosuppression on the biologic behavior of cancer. In the present study, relatively small proportions of patients were reported to have had reductions in immunosuppression, indicating that underreporting may have occurred, or alternatively, that immunosuppression reduction is not frequently prescribed.
Similar proportions of transplant recipients and general population subjects underwent surgery for prostate cancer; however, transplant recipients were more likely to receive radiation therapy, suggesting that some transplant recipients may receive more intensive anticancer therapy. However, despite receiving more therapy, transplant recipients had reduced survival from prostate cancer. It is possible that additional therapy was given to treat cancer recurrence before cancer-related deaths.
Surgery represents a major component of therapy for all the cancers studied, and therefore, its application, and just as importantly, the stage at presentation, both had significant effects on survival. These observations emphasize the importance of analyzing data regarding cancer stage at presentation.
With each additional analysis in this study, the negative effect of transplant recipient status on outcomes became increasingly apparent. The substantial preponderance of data indicates that despite having known for many years that transplant recipients are at increased risk of cancer, transplant practitioners have screened, diagnosed, and treated transplant recipients for cancer without a substantive knowledge of the potentially increased biologic aggressiveness of their cancers; or alternatively poorer outcomes because of comorbidities or lower functional status. Given these data, the approach to managing cancer in transplant recipients should now be reconsidered.
Observations from the present study can be of use in defining recommendations for cancer screening in transplant recipients. Provision of precise recommendations for individual cancers is beyond the scope of this publication; however, a few general observations can be made. With respect to each individual cancer analyzed, data from the present study indicate that transplant recipients should be considered a high-risk group for each cancer, as they develop these cancers relatively early after transplantation, and transplantation represents a significant risk factor for disease-related death. Cancers that occur at younger ages and with shorter intervals from transplantation (e.g., RCC) should require earlier screening. In addition, cancers that tend to be diagnosed at more advanced stages in transplant patients should receive more intensive screening (colon cancer, prostate cancer, breast cancer, and malignant melanoma). Cancers that behave in a more malignant fashion in transplant recipients (colon cancer, prostate cancer, breast cancer, bladder cancer, malignant melanoma, and NSCLC) may be more amenable to therapy if diagnosed earlier by more aggressive screening. Therefore, we propose that transplant recipients be considered at high risk for breast, colon, prostate, and RCC with respect to screening recommendations after transplantation.
In summary, this study has shown that several of the most common cancers are associated with significantly worse outcomes in transplant recipients compared with the general population. In addition, these cancers occurred surprisingly early after transplantation, with the median time to cancer diagnosis being less than 7 years in each cancer studied.
These observations have important implications for cancer management in transplant recipients including education, screening, and therapeutic management. Carefully designed, prospective, controlled studies are needed to evaluate the ability of immunosuppression reduction to improve outcomes from cancers arising in transplant recipients. Similarly, controlled studies should be conducted to evaluate whether additional approaches, such as conversion to mammalian target of rapamycin therapy, or more aggressive cancer therapy can improve results in transplant recipients with cancer. However, caution should be noted in exposing transplant recipients to more aggressive chemotherapy, as they have high comorbidities, and may experience increased morbidity and mortality with aggressive chemotherapy than that observed in the general population.
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Keywords:© 2009 Lippincott Williams & Wilkins, Inc.
Transplant; Malignancy; Immunosuppression