The present study sought to build upon previous research by examining hospital and physician volume as a possible explanatory variable for the disparities in outcomes after prostate surgery. We hypothesized that a portion of the racial differences in prostate cancer treatment outcomes may be explained by different probabilities of seeking care from hospitals and physicians with differing levels of experience: white men may experience better outcomes due to a greater utilization of high-volume hospitals and physicians. This hypothesis was not confirmed—the poorer outcomes experienced by black men were not explained by their differential utilization of less experienced hospitals and/or surgeons. Instead, the racial disparity in outcomes persisted regardless of hospital or physician volume.
The study results suggest that black patients were more likely to experience recurrence or death than were white patients, even when controlling for surgical volume, and confirms previous findings that demonstrate a link between prostate cancer surgical volumes and outcomes: both high physician volume and high hospital volume were associated with better outcomes.10
They also demonstrate previously-observed racial differences in both recurrence16
after surgery for prostate cancer.
Had our hypothesis been confirmed, as demonstrated through high-volume facilities and surgeons being associated with attenuation in racial differences in outcomes, our findings may have suggested an opportunity for a policy-level intervention to address racial disparities. For example, health plans—including Federal payers—could have been encouraged to improve the outcomes of their minority beneficiaries by taking a proactive role in directing them to high-volume providers. Health systems and their medical staffs would be encouraged to look internally at the hospitals and surgeons who typically serve their communities’ higher-risk populations and consider a consolidation of services to improve prostate surgery experience among, perhaps, a more limited number of their constituent hospitals and physicians. Other policy changes could encourage more experienced surgeons to consult on prostate cancer surgeries to mentor less experienced surgeons, or, similarly, encourage ongoing health education partnerships between higher and lower volume hospitals to extend the benefits of such mentoring and training to their surgeons and staff to improve patient outcomes. Although such policies may improve overall outcomes for all populations, our research shows that such interventions may be of limited utility in addressing the differences in outcomes between blacks and whites.
The decision to have surgery is a function of many known factors, including the stage of cancer, doctor recommendations, and patient preferences. Racial differences that transcend these characteristics and persist despite the experience of the provider may point to additional characteristics, such as tumor heterogeneity. Approximately 32% of black patients and 40% of white patients were classified as stage III or IV postsurgery, suggesting that white men with advanced disease were more likely than black men to receive surgery. If this were the case, one would expect white patients in this population to have less favorable outcomes in terms of recurrence, and possibly mortality. However, it is possible that surgeons are more likely to be aggressive with white patients with high-risk localized prostate cancer, which post-surgery is restaged as stage III (and up-coded in the registry data). Black patients with high risk may be guided toward, or inclined to seek, another treatment such as radiation therapy, which would not have subsequent pathologic staging (or up-coding in the registry). In addition, even within each tumor stage, tumors can vary widely with regard to tumor aggressiveness. Descriptive statistics show that blacks were more likely than whites to have poorly differentiated tumors. Thus, the blacks in our study may have had more aggressive disease within these stages.
Our study has several limitations. Volume is a proxy for experience and we examined the 8 quarters before surgery to determine volume levels. Although black men were more likely to have missing data on physician volume than were white men, additional analysis revealed no other discernible patterns in the data to suggest either its cause, the presence of bias, or any direction of bias. Also regarding volume, our data were unable to capture the absolute volume of surgeons, which would include any surgeries performed on patients who did not participate in Medicare (eg, younger than 65 years), or on individuals first diagnosed outside the SEER regions included in our study. A surgeon may also be very experienced in prostate cancer surgeries but was limited in the number performed during this study period due to a myriad of reasons. Thus, our definition of volume may be different from true experience; however, the risk and effect of bias resulting from age-limited analysis (eg, limiting to those age 65 and older) are likely to be limited when considering that previous research has found that the rank order of the hospitals by volume of surgery on patients aged 65 and older to be very similar to the rank order of the hospitals when including the absolute numbers of cancer surgeries performed (eg, all ages).9
Overall, research consistently demonstrates volume as a predictor of patient outcomes after major procedures, 8–11
warranting its merit as a proxy for experience.
Our study used claims data to measure recurrence-free survival using a method that has been validated23
and used in multiple previous studies of prostate cancer.16,21
Using this method, our measures of recurrence-free survival are likely conservative compared with true prostate cancer recurrence as this method is not able to capture recurrent disease treated with self-administered prescription drugs or those that required no treatment, such as the “watch and wait” strategy; however, the probability of these scenarios is small and, therefore, so is any likely impact on our findings.
Our decision to use tertiles as opposed to quartiles as cut-points to categorize volume preserved statistical power and precision; however, it may have done so at the risk of losing some insight into the nuances of the volume-outcome relationship. The direction of any potential bias is unclear, and extensive sensitivity analyses of the functional form of the volume measure suggest that use of tertiles was appropriate, and results using other functional forms would not alter our conclusions.
Bivariate analysis indicated that black men were more likely to see low-volume physicians, regardless of the hospital volume. It would have been interesting and may have yielded additional explanatory insight to examine the interaction of physician volume and hospital volume in the analytic model, particularly with regard to the effect of seeing low-volume physicians at high-volume hospitals, as experienced disproportionately by blacks in our study. However, study sample size precluded such examination in the analytic model. Regardless, the tendency of black men to see low-volume physicians in all settings warrants further investigation with a sufficiently large sample size to examine this question more closely.
In addition to prostate cancer-specific recurrence-free survival, overall recurrence-free survival was chosen as an end point and not prostate-specific mortality, because both hospital and physician experience with prostatectomy can influence clinical outcomes attributable to noncancer causes, such as anesthesia, perioperative mortality, and surgery-related sequelae, and this end point allows us to capture these deaths as well as mortality related directly to prostate cancer. As also found in other cancer outcomes studies, our previous research found trends and racial disparities in all-cause mortality to closely mirror prostate-cancer specific mortality,6,16
and we have no reason to believe there to be a difference or any consequent bias in this analysis, which is based on the same SEER-Medicare population.
In conclusion, racial differences in recurrence or mortality after surgery for prostate cancer did not consistently decrease with increasing hospital or physician volume as expected. Patterns of care for black men differed from white men in that they tended to undergo surgery at high-volume hospitals, and they tended to be operated on by low-volume surgeons. Thus, the poorer outcomes experienced by black men are not explained by less experienced hospitals or surgeons in these data, and so organizational or systemic interventions to address disparities through volume are not supported, while differences in basic biologic characteristics (eg, tumor aggressiveness), and social and behavioral characteristics remain likely origins of the demonstrated racial differences and points of intervention. Accordingly, future research should investigate other factors that could affect the racial disparity in recurrence and survival after prostate cancer surgery, such as lifestyle factors and clinical characteristics of the prostate tumor.