Prostate cancer control and survival in Vietnam veterans exposed to Agent Orange

How Agent Orange impacts prostate cancer risk, pathology, and treatment outcomes

Between 2.6 and 3.8 million veterans served in Vietnam while the US military dispersed Agent Orange (AO), although the exact number of exposed individuals is unknown. Agent Orange, an herbicide, is a known risk factor for various cancers, including sarcoma and leukemia, but less is known about its link with prostate cancer (PC). Prostate cancer is the most commonly diagnosed malignancy in men and the fifth most common cause of cancer-related death in men worldwide. In 2023, approximately 288,300 patients will be given a diagnosis of PC, and an estimated 34,700 fatalities will occur in the United States. However, whether the pathologic characteristics of PC among those exposed to AO differ from those in the general population remains unclear. Our review synthesizes the literature regarding the impact of AO exposure on PC incidence and disease course. A comprehensive PubMed literature search of articles published beginning in 1950 was performed using the primary search terms "Agent Orange," "TCDD," and "tetrachlorodibenzodioxin" and the secondary search terms "prostate cancer" or "prostate neoplasm." The search was limited to studies that focused on human participants and were published in English. Four authors thoroughly reviewed the retrieved articles for relevancy to the study aims: discussion of PC diagnosis, prognosis, or management among patients exposed to AO. Of 108 studies identified in our search, 13 were included in this systematic review. Findings within studies concerning AO exposure with relation to PC incidence, age at diagnosis or treatment initiation, and PC severity seemed to be mixed and generally conflicting. However, the literature seems to indicate that there are no significant differences in survivorship between exposed and unexposed veterans who are given a diagnosis of PC. Given these heterogeneous outcomes, the evidence does not encourage a significantly different approach to the diagnosis and management of PC for veterans exposed to AO. Clinicians should make case-by-case decisions regarding PC screening and potential treatment options for this patient group, weighing clinical suspicion against the harms of diagnostic workup and treatment.

The Stage at Presentation and Oncologic Outcomes for Agent Orange Exposed and Non-Exposed United States Veterans Diagnosed With Prostate Cancer

INTRODUCTION

It is unknown if Agent Orange (AO)-exposed veterans have worse outcomes than unexposed Veterans after prostate cancer treatment. We evaluated oncologic outcomes based on AO exposure history, accounting for known prognostic covariates not previously studied.

METHODS

US military Veterans diagnosed with prostate adenocarcinoma born between 1930 and 1956 were identified from our prospectively gathered institutional database. Evaluable patients had to have known AO exposure status, age, National Comprehensive Cancer Network risk group, Charlson comorbidity score, smoking status, and type of initial therapy. The risk of death, metastasis, and progression stratified by initial therapy was analyzed using Cox regression.

RESULTS

Seventy AO-exposed and 561 non-exposed Veterans were identified (median follow-up, 10.0 years). AO-exposed veterans (AOeV) were slightly younger (64.0 vs 65.7 years; P = .013) at diagnosis and presented at more advanced stages (stage 4: 14.3% vs 2.5%) than non-AOeV. There was no difference for overall survival (hazard ratio [HR], 0.86; P = .576; metastasis-free survival (HR, 1.5; P = .212), or progression-free survival (HR, 0.67; P = .060) between AOeV vs non-AOeV in analyses stratified by treatment received accounting for other prognostic covariates. Cigarette smoking was associated with a 2- to 3-fold increased risk of death over those who quit or never smoked.

CONCLUSION

Although AOeV do present at a younger age and higher clinical stages than non-AOeV, the oncologic outcomes after accounting for treatments received and other prognostic covariates are similar.

The Effect of Radium-223 Therapy in Agent Orange-Related Prostate Carcinoma

Background

Radium-223 (Ra-223) radioisotope has been reported to increase median survival in bone metastatic prostate carcinoma. The addition of Ra-223 to abiraterone was associated with an increased risk of bone fractures. There has been no comprehensive data for using Ra-223 in veterans who were exposed to Agent Orange (AO+).

Methods

We present a retrospective study of veterans with bone metastatic castration-resistant prostate cancer (CRPC) who received standard doses of Ra-223 and other sequential therapies at US Department of Veterans Affairs Pittsburgh Healthcare System in Pennsylvania from January 2014 to January 2019. Veterans were divided into 2 groups: those who were exposed to Agent Orange (AO+) and those who had no exposure (AO-). Time to study was calculated from the initiation of Ra-223. Time to skeletal-related events (SRE), progression of prostate specific antigen (PSA), bone metastasis, and alkaline phosphatase (ALP) were calculated in months using unpaired t test with 2-tailed P values. Median survival was calculated by Kaplan Meier R log-rank test.

Results

There were 34 veterans with bone metastatic CRPC: 17 veterans (50%) were AO+ and 17 veterans (50%) were AO-. The mean age of diagnosis of AO+ veterans was 62 years and 69 years (P = .005) for AO- veterans (the mean Gleason score 8.2 and 8.0, respectively [P = .71]). The median number of Ra-223 cycles was 6 (60%). Ten veterans received Ra-223 as first line (29%) and 24 veterans received Ra-223 later (71%). There were 12 SREs with median survival of 15 months. There was no difference in mean time to SRE between AO+ (8 veterans, 10.6 months) and AO- (4 veterans, 10.3 months) (P = .93). The mean time to PSA progression for AO+ was 5.4 months and AO- was 6.8 months (P = .28). Mean time to bone progression for AO+ was 7.6 months and AO- was 10.1 months (P = .16). Mean time to ALP progression for AO+ and AO- was 6.3 months and 8.7 months, respectively (P = .05). Twenty veterans (58%) had died. Median survival for Ra-223 first was 32 months and for Ra-223 later was 15 months (P = .14; hazard ratio [HR] 0.48; 95% CI, 0.17-1.3). Median survival for AO+ and AO- veterans was 12 months and 18 months, respectively (P = .15; HR, 2.0; 95% CI, 0.77-5.0).

Conclusions

There was no statistical difference between AO+ and AO- veterans in terms of time to SRE, PSA, bone and ALP progression, even though there was a trend of shorter duration in AO+ veterans. There was no median survival difference between Ra-223 first vs Ra-223 later as well as between AO+ and AO- but there is a trend of worse survival in AO+ veterans.

A critical review of the epidemiology of Agent Orange/TCDD and prostate cancer

To inform risk assessment and regulatory decision-making, the relationship between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and prostate cancer requires clarification. This article systematically and critically reviews the epidemiologic evidence on the association between exposure to TCDD or Agent Orange, a TCDD-contaminated herbicide used during the Vietnam War, and prostate cancer risk. Articles evaluated include 11 studies of three cohorts, four case-control or cross-sectional studies, and three case-only studies of military veterans with information on estimated Agent Orange or TCDD exposure; 13 studies of seven cohorts, one case-control study, and eight proportionate morbidity or mortality studies of Vietnam veterans without information on Agent Orange exposure; 11 cohort studies of workers with occupational exposure to TCDD; and two studies of one community cohort with environmental exposure to TCDD. The most informative studies, including those of Vietnam veterans involved in Agent Orange spraying or other handling, herbicide manufacturing or spraying workers with occupational TCDD exposure, and community members exposed to TCDD through an industrial accident, consistently reported no significant increase in prostate cancer incidence or mortality. Only some potentially confounded studies of Vietnam veterans compared with the general population, studies with unreliable estimates of Agent Orange exposure, and analyses of selected subgroups of Vietnam veterans reported positive associations. Overall, epidemiologic research offers no consistent or convincing evidence of a causal relationship between exposure to Agent Orange or TCDD and prostate cancer. More accurate exposure assessment is needed in large epidemiologic studies to rule out a causal association more conclusively.