Racial Differences in CYP3A4 Genotype and Survival Among Men Treated on Radiation Therapy Oncology Group (RTOG) 9202: A Phase III Randomized Trial

Prostate Cancer, Race, and Health Disparity: What We Know

ABSTRACT

Prostate cancer (PCa) in African American men is one of the most common cancers with a great disparity in outcomes. The higher incidence and tendency to present with more advanced disease have prompted investigators to postulate that this is a problem of innate biology. However, unequal access to health care and poorer quality of care raise questions about the relative importance of genetics versus social/health injustice. Although race is inconsistent with global human genetic diversity, we need to understand the sociocultural reality that race and racism impact biology. Genetic studies reveal enrichment of PCa risk alleles in populations of West African descent and population-level differences in tumor immunology. Structural racism may explain some of the differences previously reported in PCa clinical outcomes; fortunately, there is high-level evidence that when care is comparable, outcomes are comparable.

Prostate Cancer Racial Disparities: A Systematic Review by the Prostate Cancer Foundation Panel

CONTEXT

Prostate cancer (PCa) is a complex disease that disproportionately impacts Black men in the USA. The structural factors that drive heterogeneous outcomes for patients of differing backgrounds are probably the same ones that result in population-level disparities. The relative contribution of drivers along the PCa disease continuum is an active area of investigation and debate.

OBJECTIVE

To critically synthesize the available evidence on PCa disparities from a population-level perspective in comparison to data from "equal access and equal care settings" and to provide a consensus summary of the state of PCa disparities.

EVIDENCE ACQUISITION

A plenary panel on PCa disparities presented at the Prostate Cancer Foundation meeting on October 24, 2019 and ensuing discussions are reported here. We used a systematic literature review approach and the Preferred Reporting Items for Systematic Reviews and Meta-analyses to select the most relevant publications. A total of 3333 publications between 2011 and 2021 were retrieved, of which 52 were included in the review; an additional 13 articles on screening guidelines, seminal clinical trials, and statistical methodology were used in the evidence synthesis.

EVIDENCE SYNTHESIS

Race disparities in PCa are a result of a complex interaction between socioeconomic factors impacting access to care and ancestral/genetic factors that may influence tumor biology. Black men in the USA continue to have a nearly 1.8 times higher population-level mortality rate than White men. Failure to account for the race-specific incidence burden would continue to lead to residual disparity even after achieving relatively similar outcomes after primary treatment, resulting in a higher long-term mortality burden. Selection bias remains possible in PCa studies, which often rely on highly specific cohorts of Black men with higher use of health care resources that may not represent the average Black patient in the USA. Novel methods including mediation analysis and genetic ancestry rather than self-identified race can optimize analytical models investigating racial disparities and may lead to a better understanding of PCa genomic diversity and behavior.

CONCLUSIONS

Our findings emphasize the importance of racially diverse studies, including precision -omics, prevention, and targeted therapy initiatives, to elucidate mechanisms underlying racial differences in outcomes and response to therapy. We propose novel approaches for studying and addressing PCa disparities. Contemporary methods, particularly in the domain of mediation analysis, can promote scientific rigor in understanding these disparities.

PATIENT SUMMARY

Inaccurate data interpretation or lack of data altogether for Black men can impact policy and ultimately affect millions of individuals of African origin worldwide. Our review identifies a need to develop and prioritize a strategy for including Black and other men with prostate cancer in intervention studies and randomized clinical trials to halt the widening prostate cancer disparities.

Assessment of inter-racial variability in CYP3A4 activity and inducibility among healthy adult males of Caucasian and South Asian ancestries

PURPOSE

Cytochrome P450 (CYP) 3A4 is responsible for the metabolism of more than 30% of clinically used drugs. Inherent between subject variability in clearance of CYP3A4 substrates is substantial; by way of example, midazolam clearance varies by > 10-fold between individuals before considering the impact of extrinsic factors. Relatively little is known about inter-racial variability in the activity of this enzyme.

METHODS

This study assessed inter-racial variability in midazolam exposure in a cohort (n = 30) of CYP3A genotyped, age-matched healthy males of Caucasian and South Asian ancestries. Midazolam exposure was assessed at baseline, following 7 days of rifampicin and following 3 days of clarithromycin.

RESULTS

The geometric mean baseline midazolam area under the plasma concentration curve (AUC_0-6) in Caucasians (1057 μg/L/min) was 27% greater than South Asians (768 μg/L/min). Similarly, the post-induction midazolam AUC_0-6 in Caucasians (308 μg/L/min) was 50% greater than South Asians (154 μg/L/min), while the post-inhibition midazolam AUC_0-6 in Caucasians (1834 μg/L/min) was 41% greater than South Asians (1079 μg/L/min). The difference in baseline AUC_0-6 between Caucasians and South Asians was statistically significant (p ≤ 0.05), and a trend toward significance (p = 0.067) was observed for the post-induction AUC_0-6 ratio, in both unadjusted and genotype adjusted analyses.

CONCLUSIONS

Significantly higher midazolam clearance was observed in healthy age-matched males of South Asian compared to Caucasian ancestry that was not explained by differences in the frequency of CYP3A genotypes.

Racial Differences in the Diagnosis and Treatment of Prostate Cancer

Disparities between African American and Caucasian men in prostate cancer (PCa) diagnosis and treatment in the United States have been well established, with significant racial disparities documented at all stages of PCa management, from differences in the type of treatment offered to progression-free survival or death. These disparities appear to be complex in nature, involving biological determinants as well as socioeconomic and cultural aspects. We present a review of the literature on racial disparities in the diagnosis of PCa, treatment, survival, and genetic susceptibility. Significant differences were found among African Americans and whites in the incidence and mortality rates; namely, African Americans are diagnosed with PCa at younger ages than whites and usually with more advanced stages of the disease, and also undergo prostate-specific antigen testing less frequently. However, the determinants of the high rate of incidence and aggressiveness of PCa in African Americans remain unresolved. This pattern can be attributed to socioeconomic status, detection occurring at advanced stages of the disease, biological aggressiveness, family history, and differences in genetic susceptibility. Another risk factor for PCa is obesity. We found many discrepancies regarding treatment, including a tendency for more African American patients to be in watchful waiting than whites. Many factors are responsible for the higher incidence and mortality rates in African Americans. Better screening, improved access to health insurance and clinics, and more homogeneous forms of treatment will contribute to the reduction of disparities between African Americans and white men in PCa incidence and mortality.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

Genomic and Histopathological Tissue Biomarkers That Predict Radiotherapy Response in Localised Prostate Cancer

Localised prostate cancer, in particular, intermediate risk disease, has varied survival outcomes that cannot be predicted accurately using current clinical risk factors. External beam radiotherapy (EBRT) is one of the standard curative treatment options for localised disease and its efficacy is related to wide ranging aspects of tumour biology. Histopathological techniques including immunohistochemistry and a variety of genomic assays have been used to identify biomarkers of tumour proliferation, cell cycle checkpoints, hypoxia, DNA repair, apoptosis, and androgen synthesis, which predict response to radiotherapy. Global measures of genomic instability also show exciting capacity to predict survival outcomes following EBRT. There is also an urgent clinical need for biomarkers to predict the radiotherapy fraction sensitivity of different prostate tumours and preclinical studies point to possible candidates. Finally, the increased resolution of next generation sequencing (NGS) is likely to enable yet more precise molecular predictions of radiotherapy response and fraction sensitivity.

Tissue biomarkers for prostate cancer radiation therapy

Prostate cancer is the most common cancer and second leading cause of cancer deaths among men in the United States. Most men have localized disease diagnosed following an elevated serum prostate specific antigen test for cancer screening purposes. Standard treatment options consist of surgery or definitive radiation therapy directed by clinical factors that are organized into risk stratification groups. Current clinical risk stratification systems are still insufficient to differentiate lethal from indolent disease. Similarly, a subset of men in poor risk groups need to be identified for more aggressive treatment and enrollment into clinical trials. Furthermore, these clinical tools are very limited in revealing information about the biologic pathways driving these different disease phenotypes and do not offer insights for novel treatments which are needed in men with poor-risk disease. We believe molecular biomarkers may serve to bridge these inadequacies of traditional clinical factors opening the door for personalized treatment approaches that would allow tailoring of treatment options to maximize therapeutic outcome. We review the current state of prognostic and predictive tissue-based molecular biomarkers which can be used to direct localized prostate cancer treatment decisions, specifically those implicated with definitive and salvage radiation therapy.

Impact of race on biochemical disease recurrence after prostate brachytherapy

BACKGROUND

Understanding racial differences in disease presentation and response to therapy is necessary for the effective treatment and control of prostate cancer. In this study, the authors examined the influence of race on biochemical disease-free survival (BDFS) among men who received prostate brachytherapy.

METHODS

In total, 2301 men were identified who had a minimum follow-up of 24 months and had received low-dose-rate brachytherapy for prostate cancer at the Mount Sinai Medical Center from June 1990 to October 2008. Patient factors, with specific emphasis on patient race, were analyzed with respect to freedom from biochemical failure (FFbF). Kaplan-Meier analyses, life-tables, and log-rank tests were used to identify variables that were predictive of 10-year FFbF.

RESULTS

In this series, a total of 2268 patients included 81% Caucasians, 12% African Americans, 6% Hispanics, and 1% Asians. The 10-year actuarial FFbF rate was 70% for AA men and 84% for all others (P = .002). Between Caucasian men and AA men, the 10-year FFbF rate was 83% versus 70%, respectively (P = .001).There was no significant difference in 10-year FFbF between Caucasian men and Hispanic men (83% vs 86%, respectively; P = .6). The 10-year FFbF rate for Hispanic men and AA men was 86% versus 70%, respectively (P = .062). A greater percentage of AA men presented with higher prostate-specific antigen levels (PSA) (>10 ng/mL; 44% vs 21%; P < .001) and, thus, with higher risk disease (24% vs 15%; P < .001) compared with Caucasian men. Among the men with low-risk disease, the 10-year FFbF rate was 90% for Caucasian men and 76% for AA men (P = .041). The 10-year BDFS rate for patients who received brachytherapy alone was 86% for Caucasian men and 61% for AA men (P = .001); however, this difference was not observed when brachytherapy was combined with androgen-deprivation therapy(ADT) with or without supplemental external-beam radiotherapy (EBRT). Multivariate analysis revealed that PSA (P = .024), Gleason score (P < .001), the biologic effective dose (P < .001), EBRT (P = .002), ADT (P = .03), and AA race (P = .037) were significant predictors of 10-year FFbF. No significant differences was observed in overall survival, cause-specific survival, or distant metastasis-free survival between racial groups.

CONCLUSIONS

AA race appeared to be an independent negative predictor of BDFS after prostate brachytherapy, and this result may highlight the need for more aggressive therapy in this patient population.

Interactions among genes, tumor biology and the environment in cancer health disparities: examining the evidence on a national and global scale

Cancer incidence and mortality rates show great variations across nations and between population groups. These variations are largely explained by differences in age distribution, diet and lifestyle, access to health care, cultural barriers and exposure to carcinogens and pathogens. Cancers caused by infections are significantly more common in developing than developed countries, and they overproportionally affect immigrant populations in the USA and other countries. The global pattern of cancer is not stagnant. Instead, it is dynamic because of fluctuations in the age distribution of populations, improvements in cancer prevention and early detection in affluent countries and rapid changes in diet and lifestyle in parts of the world. For example, increased smoking rates have caused tobacco-induced cancers to rise in various Asian countries, whereas reduced smoking rates have caused these cancers to plateau or even begin to decline in Western Europe and North America. Some population groups experience a disproportionally high cancer burden. In the USA and the Caribbean, cancer incidence and mortality rates are excessively high in populations of African ancestry when compared with other population groups. The causes of this disparity are multifaceted and may include tumor biological and genetic factors and their interaction with the environment. In this review, we will discuss the magnitude and causes of global cancer health disparities and will, with a focus on African-Americans and selected cancer sites, evaluate the evidence that genetic and tumor biological factors contribute to existing cancer incidence and outcome differences among population groups in the USA.

Predictive models in external beam radiotherapy for clinically localized prostate cancer

Predictive models are being used increasingly in effort to allow physician and patient expectations to be aligned with outcomes that are based on available data. Most predictive models for men who receive external beam radiotherapy for clinically localized prostate cancer are based on Gleason score, clinical tumor classification, and prostate-specific antigen (PSA) levels. More sophisticated models also have been developed that incorporate treatment-related variables, such as the dose of radiation and the use of androgen-deprivation therapy. Most of the predictive models applied to prostate cancer were derived using PSA recurrence rates as the major endpoint, but clinical endpoints have been incorporated increasingly into predictive models. Biomarkers also are increasingly being added to predictive models in an effort to strengthen them. The Radiation Therapy Oncology Group (RTOG) has completed studies on a wide range of markers using tissue from 2 phase 3 trials (RTOG 8610 and 9202). To date, preliminary assessments of p53; DNA ploidy; p16/retinoblastoma 1 protein; Ki-67; mouse double-minute p53 binding protein homolog; Bcl-2/Bcl-2-associated X protein; cytosine, adenine, and guanine repeats; cyclooxygenase-2; signal transducer and activator of transcription 3; cytochrome P450 3A4; and protein kinase A have been completed. Although they are not ready for widespread, routine use, there are reasons to believe that future models will combine these markers with traditional pretreatment and treatment-related variables and will improve our ability to predict outcome and select the optimal treatment. Cancer 2009;115(13 suppl):3112-20. (c) 2009 American Cancer Society.

Adjuvant radiotherapy and chemotherapy for pancreatic carcinoma: the Mayo Clinic experience (1975-2005)

PURPOSE

To determine prognostic factors and impact of adjuvant chemotherapy (CT) and radiotherapy (RT) on overall survival (OS) after resection of pancreatic adenocarcinoma.

PATIENTS AND METHODS

We performed a retrospective review 472 consecutive patients who underwent complete resection with negative margins (R0) for invasive carcinoma (T1-3N0-1M0) of the pancreas between 1975 and 2005 at the Mayo Clinic in Rochester, MN. Exclusion criteria included metastatic or unresectable disease at surgery, positive surgical margins, and indolent tumor types (islet cell tumors and mucinous cystadenocarcinoma). Median RT dose was 50.4 Gy in 28 fractions; 98% of RT patients also received concurrent fluorouracil-based CT.

RESULTS

Six patients died within 30 days of surgery. For the 466 surviving patients, median follow-up was 32.4 months; median OS was 21.6 months. Median OS after adjuvant CT-RT was 25.2 versus 19.2 months after no adjuvant therapy (P = .001). Two-year OS was 50% versus 39%, and 5-year OS was 28% versus 17%. Adverse prognostic factors identified by univariate and multivariate analysis included positive lymph nodes (risk ratio [RR] = 1.3; P < .001), high histologic grade (RR = 1.2; P < .001), and no adjuvant therapy (RR = 1.3; P < .001). Tumor extension beyond the pancreas was an adverse prognostic factor by univariate analysis alone (P = .03). Patients receiving adjuvant therapy had more adverse prognostic factors than those not receiving adjuvant therapy (P = .001).

CONCLUSION

This study represents one of the largest, single-institution, retrospective reviews of adjuvant therapy in patients after R0 resection of carcinoma of the pancreas. Overall survival was better in patients who received adjuvant CT-RT.