New evidence for the relationship between PSA value and BMI in diagnosing prostate cancer: obesity should be reckoned

Sir,

We read with great interest the paper by Oh et al. [1] and the paper by Pater et al. [2]. Their study confirmed the previously reported inverse relationship between prostate-specific antigen (PSA) value and body mass index (BMI). Indeed, they indicated a decrease in PSA for an increasing BMI with a 0.026 decrease in PSA for every unit increase in BMI. To date, the detection of prostate cancer (PCa) has become more common since the introduction of PSA, but overall mortality remains high with an estimated 27,360 deaths in 2009, and relative survival of patients diagnosed with prostate cancer has changed little.

One possible reason that screening for PCa using PSA has not achieved reduced mortality is that PSA can be confounded by weight. In fact, several previous studies have demonstrated an inverse association between PSA and BMI. Kim et al. demonstrated that PSA shows a significant linear trend only in the group with a BMI ≥ 25 kg/m with prostate examination [3].

Pater et al. investigated 767 patients, with mean BMI 28.7 kg/m²; where 78% were overweight or obese (BMI ≥25). Mean PSA was 1.28 ng/ml. Notably, 44 patients had at least 1 PSA level over 4.0 ng/ml [2]. There was a small, but statistically significant trend toward decreasing PSA for an increasing BMI.

However, multiple findings showed that obese men had lower serum PSA concentrations than normal weight men. PSA mass tended to be lower in obese patients, but is unlikely to be a consequence of lower serum testosterone concentrations. Oh et al. declared that the accuracy of PSA in predicting PCa did not change regardless of BMI category in Asian men [1]. Recently it was shown that initial PSA levels of 3471 patients were <30 ng/ml, undergoing multicore (≥12) transrectal ultrasound-guided prostate biopsy. The median PSA level in each BMI category was 7.84, 7.75, 7.33 and 5.79 ng/ml with BMI of <23, 23-24.9, 25-29.9, and ≥30 kg/m² respectively [1]. Therefore, it may be suggested that the PSA threshold should be lower in obese men to discriminate between PCa and benign conditions in the real clinical situation. Similarly, Yang et al. recruited 20,509 native Korean men and found a statistically significant trend towards a lower likelihood of having a serum PSA level ≥2.5 ng/ml with an increased BMI [4]. These results might affect PCa screening using serum total PSA. Indeed, the relationship between obesity and PSA is confounded by a number of factors, which likely explain the observed inverse association previously reported. These data showed that obesity can help clinical staff to interpret the value of PSA in screening for PCa. Meanwhile, Li et al. demonstrated the inverse relationship between PSA concentration and BMI, and hold that this might be explained by a hemodilution effect among obese men. A value between 3.32 and 3.68 ng/ml might be recommended for PSA screening in middle-aged obese Asian men [5].

Of note, a recent study showed that the result accuracy of PSA as a predictor of PCa in 917 Italian men, performing trans-rectal ultrasound-guided prostate needle biopsy, is not significantly altered by BMI. Bañez et al. highlighted that obesity does not negatively impact the overall ability of PSA to discriminate between PCa and benign conditions [6].

In summary, available evidence has demonstrated an inverse relationship between PSA and BMI. However, much of the data regarding the role of PSA in obese patients with PCa has been obtained from distinct populations and proves controversial. Therefore, further clinical studies may be required to explore comprehensively the accurate diagnosis of prostate cancer in obese men in the real clinical situation.

Chang-ming Lin^1,2, Chao-zhao Liang¹*

¹Department of Urology, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230032, China, ²Department of Urology, The Central Hospital of Maanshan The Affiliated Hospital of Wannan Medical College,Maanshan, Anhui 243011, China

^*Correspondence: Chao-zhao Liang, e-mail: [email protected]

References

1. Oh JJ, Jeong SJ, Lee BK et al. Does obesity affect the accuracy of prostate-specific antigen (PSA) for predicting prostate cancer among men undergoing prostate biopsy. BJU Int 2013; 112: E265–E271
2. Pater LE, Hart KW, Blonigen BJ, Lindsell CJ, Barrett WL. Relationship between prostate-specific antigen, age, and body mass index in a prostate cancer screening population. Am J Clin Oncol 2012; 35: 490–492
3. Kim JH, Doo SW, Yang WJ, Song YS, Kwon SS. Prostate-specific antigen density: a better index of obesity-related PSA decrease in ostensibly healthy Korean men with a PSA <3.0 ng/mL. Urology 2013; 81: 849–852
4. Yang WJ. The likelihood of having a serum PSA level of >/=2.5 or >/=4.0 ng ml^-1 according to obesity in a screened Korean population. Asian J Androl 2013; 15: 770–772
5. Li F, Shen Z, Lu Y, Yun J, Fan Y. Serum prostate-specific antigen concentration and hemodilution among Chinese middle-aged obese men: a hematocrit-based equation for plasma volume estimation is induced. Cancer Epidemiol Biomarkers Prev 2012; 21: 1731–1734
6. Bañez LL, Albisinni S, Freedland SJ, Tubaro A, De Nunzio C. The impact of obesity on the predictive accuracy of PSA in men undergoing prostate biopsy. World J Urol 2012; doi: 10.1007/s00345-012-0919-9