1. Nalley, Catlin

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A recent study suggests that the lower rate of PSA screening among smokers could partially explain the inverse association of smoking with total and low-grade/stage prostate cancer, according to findings presented during the virtual 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved (Abstract PO-204).

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The researchers also reported that-independent of PSA screening-smoking was associated with a higher risk of metastatic prostate cancer and disease mortality.


"Evidence regarding the association of cigarette smoking and prostate cancer risk has been mixed, and mostly based on studies in White populations," noted study author and presenter Anqi Wang, a PhD student at the Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California, Los Angeles.


"To provide additional information of this topic, we assessed the relation between smoking and prostate cancer risk and mortality in a large multiethnic population, while considering the confounding effect of PSA screening," she explained.


Research Methods & Key Results

The researchers included 74,598 White, African-American, Native Hawaiian, Japanese American, and Latino men without a prostate cancer diagnosis at baseline of the Multiethnic Cohort Study.


Smoking status was acquired through a baseline questionnaire, and the investigators specifically examined the following: smoking status (never, former, current), cigarette per day, pack-year, smoking duration, total nicotine equivalents, time since quitting, and age started smoking. Total nicotine equivalents for smokers were inputted by an algorithm developed based on a subset of participants, the study authors outlined.


The outcome of interest, according to Wang, was incidence of prostate cancer, as well as the stage and Gleason grade at the time of diagnosis. This was identified by cohort linkage to the SEER cancer registries in the states of Hawaii and California (1993-2017).


"Deaths within the cohort were obtained from death certificate files in Hawaii and California, and supplemented with linkages to the National Death Index," Wang explained. "We defined aggressive prostate cancer as either regional or metastatic disease, or localized disease with a Gleason score of more than 8."


The research team used Cox proportional hazards regression model with age since study entry as the time metric, according to Wang. During 21.5 years of follow-up, they documented 8,696 prostate cancer cases and 1,171 deaths from prostate cancers, the study authors stated. Overall, the researchers reported that 52.0 percent and 18.0 percent of the study population were current and former smokers, respectively. African Americans had the highest proportion of ever smokers (75.6%), while their White counterparts had the lowest proportion (67.7%), the study authors wrote.


When discussing the result of smoking status and prostate cancer outcomes, Wang noted that both current and former smokers had a lower risk of total prostate cancer, as well as low-grade and localized prostate cancers, compared to never smokers. Also, the researchers observed that smokers were more likely to have metastatic prostate cancer and are more likely to die from their disease.


"For the smoking intensity and prostate cancer, we can see that for those people who have a higher smoking intensity-[as measured by greater pack-year]-they were less likely to develop total and localized prostate cancer, they are more likely to develop metastatic prostate cancer, and they're more likely to die from prostate cancer," Wang noted during her presentation. "A similar trend was observed for pack-year, duration, total nicotine equivalents, time since quitting, and time started smoking.


"When stratified by race/ethnicity, current African-American smokers did not show as strong an inverse association with total prostate cancer as current smokers in other races/ethnicities," she said. "However, for prostate cancer mortality, we see a similar trend across the five [race/ethnicity] groups."


Among men who completed a question regarding PSA screening history (n=56,435), the researchers found that current smokers had lower odds of reporting a PSA test compared with never smokers, while former smokers had higher odds.


"In stratifying by PSA screening history, the results for men without a PSA screening were similar to the main analysis," the study authors explained. "However, among men who reported PSA screening, the inverse associations between smoking and risk of total, low-grade, and localized prostate cancer were closer to null, while the associations with metastatic prostate cancer and prostate cancer mortality were positive and consistent with the main results."


Concluding her presentation, Wang stated, "PSA screening may explain a small fraction of the inverse association of smoking with low-grade or stage prostate cancer and the positive association with metastatic prostate cancer and prostate cancer mortality. We will explore other potential detection biases and biological mechanisms for the association between smoking and prostate cancer in the next step."


Catlin Nalley is a contributing writer.