In this population-based study, we investigated whether the survival and mortality outcomes in elderly male patients (aged ≥70 years) with localized PCa is different between those managed by primary observation and those undergoing primary ADT over a long period of time. We showed that the overall SMR of patients in the observation cohort was lower than those in the ADT cohort in both age groups over the entire study period. PCSM and mortality due to causes other than PCa were lower in patients monitored with primary observation compared to those managed with primary ADT. This difference was particularly evident in patients aged 70–79 years at the time of diagnosis. Overall survival was also higher in subjects in this age group managed by primary observation. By contrast, a smaller difference in PSCM was observed between patients undergoing ADT and those managed by primary observation, while a clear difference in mortality due to other causes was not seen in patients aged 80 or older. This implies a better general health condition and a healthier lifestyle among patients in the observation cohort.
An increased risk of PCSM was observed in patients undergoing primary ADT compared to those managed by primary observation, while a lower risk of other-cause mortality was seen in the younger patient group managed by primary observation. This suggests that in recent times, primary ADT without curative treatment was generally selected for patients with aggressive disease. A 10-year threefold risk of PCSM was associated with poorly differentiated PCa among patients with conservatively managed localized PCa in the Surveillance, Epidemiology, and End Results (SEER) Program [15]. Most male patients with conservatively managed localized PCa aged >66 years with competing comorbidities died from causes other than PCa in a period of 10 years, irrespective of age and tumor aggressiveness [16]. The use of primary ADT was beneficial for patients with aggressive disease and few comorbidities [16]. However, overall mortality was lower in subjects managed by observation than with ADT. We assumed that a shift from ADT to a more radical treatment may have occurred in patients with a good general health status. Since an increasing number of PCa cases has been diagnosed in recent years, and observation is widely utilized in Finland, it is likely that observation was selected for patients with less aggressive histology and without advanced disease. Consequently, fewer male patients died of cancer owing to the slow, natural course of disease.
Overall survival was reduced in patients aged 70–79 years initially treated with. It is still difficult to draw a conclusion from this finding owing to the absence of data on patient comorbidities. However, increased morbidity and mortality from ADT-related side effects is possible. Thus, the survival benefits of ADT are partly offset by its high toxicity. These findings can also be explained by a better general health condition among patients in the observation group. In our cohort, patients in the observation group had a clearly lower risk of overall mortality compared to patients undergoing primary ADT. Since in epidemiological studies the only endpoint that is free from bias is mortality, we can assume that patients in observation cohort were healthier than those in the ADT cohort.
Many population-based analyses suggest that gonadotropin-releasing hormone (GnRH) agonist use is associated with a greater risk of coronary artery disease, myocardial infarction, and diabetes mellitus (DM) [17–19]. Subsequent reports have suggested that male patients with comorbidities or prior cardiovascular disease treated with GnRH agonists might be at increased risk of cardiovascular mortality [20, 21]. Based on these observations, a science advisory consensus statement on GnRH agonist therapy and cardiovascular risk was issued, together with a U.S. Food and Drug Administration safety warning to address concerns of increased risk of myocardial infarction, stroke, sudden cardiac death, and DM [22]. However, conflicting results have been reported. In a recent meta-analysis, ADT use was not associated with an increased risk of cardiovascular death, but with a lower risk of PCSM and all-cause mortality [23]. Studer et al. also reported that ADT for localized PCa may even reduce cardiovascular mortality if started immediately after diagnosis [24].
The current study findings did not support the life-prolonging effects of primary ADT for localized PCa. Several reports have shown similar results: In a prior population-based cohort study on 66717 Medicare patients diagnosed between 1992 and 2009, and who received no definitive local therapy within 180 days of prostate cancer diagnosis, primary ADT was not associated with improved overall long-term CSS or the CSS of patients with localized PCa [25]. Instead, there is evidence that primary ADT led to inferior outcomes [24]. Low overall survival rates were reported for male patients with localized disease treated with primary ADT rather than observation in a previous population-based study [26]. In addition, Potosky et al. reported that primary ADT was neither associated with an enhanced risk of all-cause mortality (hazard ratio [HR] of 1.04, 95% CI: 0.97–1.11) nor PCa-specific mortality (HR of 1.03; 95% CI: 0.89–1.19) after adjusting for the sociodemographic and clinical characteristics of patients with localized PCa. However, primary ADT was associated with a decreased risk of all-cause mortality, but not PCSM, among patients at high risk of PCa progression [27].
PSA screening practices have increased exponentially over a 30-year period, and regular PSA testing is used frequently among all socioeconomic groups in Scandinavia and Finland [28, 29]. In the early years of the present study, a diagnosis of localized PCa was generally performed via a digital rectal examination or using pathological specimens obtained following a transurethral resection of the prostate. In recent years, most localized PCa cases have been diagnosed by prostate biopsies prompted by elevated PSA values. Moreover, although a proven benefit of the PSA screening of older males has not been shown, PSA testing is frequently performed for elderly patients [30]. The wide-stage migration of PCa from advanced to indolent disease has been reported over ≥20 years [31]. Thus, a commonly employed but poorly organized screening policy explains the increased rate of PCa in past decades in Finland. Consequently, the number of elderly male patients with PCa has also increased. This implies that the more favorable outcomes associated with the use of primary observation compared to ADT in patients with PCa, especially those in their 70s, can be attributed to PSA-related “lead time” rather than life extension.
Over the study period, staging of metastatic disease in Finland was performed by bone scan examination according to national guidelines until the mid-2000s, after which low-risk PCa patients typically underwent no imaging. The proportion of de novo metastatic PCa in Finland was nearly one-third from 1985 to 1994. This implies that staging procedures of PCa by bone scans were widely performed even in the earlier years of the study period, suggesting a good quality of the TNM classification data of PCa in the Finnish Cancer Registry database. In the Finnish Cancer Registry reports, the proportion of de novo metastatic PCa has recently been around 17%, higher than in Sweden [32], where the incidence of PCa is high and PSA screening is widely performed. This might also indicate a more aggressive PCa histology in cases that are classified as localized by the TNM system, and thus more commonly treated with immediate ADT than cases with less aggressive histology.
A few points are worthy of further consideration. As information on patient comorbidities and detailed PCa characteristics (i.e., Gleason scores and PSA values) was not collected, it was not possible to adjust for differences in morbidity and mortality with a potential link to ADT. Thus, a comparison of study outcomes in terms of PCSM and overall survival between the different groups was not possible. Also, due to the absence of data on patient comorbidities and PCa characteristics, it was not possible to determine who would benefit from primary ADT in localized PCa. However, propensity score matching, particularly when applied to socioeconomic status/education level, may have mitigated some of the comorbidity-related limitations. Detailed information on cancer treatment was also incomplete for both treatment groups. Although men in the observation group did not receive ADT or radical treatment in the four months following diagnosis, it is conceivable that some of them may have received treatment later. This limitation may have had a substantial effect on the study outcomes. Furthermore, although the study population included patients with localized PCa, the reliability of the staging procedures over time is debatable. TNM staging was based on mandatory reports obtained from hospitals and pathological laboratories. In other words, clinical practices in Finland were governed by national and/or European prostate cancer guidelines of the time. Consequently, the risk of metastases was evaluated according to these guidelines.
Notwithstanding these limitations, the study had several strengths. It was an observational population-based study estimating trends in cancer survival and mortality over time. While we did not directly compare different types of cancer treatments, population-based cohorts yield important information about PCa treatment in real-life situations, as the populations in randomized controlled trials are selected using stringent criteria by excluding out substantial proportion of real-life patients. However, in population-based studies patients are also allocated to different treatments, and results based on those can be subject to errors when comorbidities are involved. From an epidemiological perspective, these data determine the Finnish results obtained for patients managed with primary ADT or by observation. This study was based on nationwide data for PCa and included nearly 100% of patients in Finland over a nearly 30-year period. No previous population-based results from Finland on this subject have been published. Similar complete population-based coverage is not available in many European countries.