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Page 6 of 9 Zaichick et al. J Cancer Metastasis Treat 2019;5:48 I http://dx.doi.org/10.20517/2394-4722.2019.07

From Table 4, it is observed that in EPF samples of PCa group the concentrations of Rb and Zn are 3.2 and
7.7 times, respectively, lower than levels of these trace elements in EPS of patients with BPH.

The range of means of Zn concentration reported in the literature for EPF of untreated hyperplastic prostate
(from 268 mg/L to 9,870 mg/L) and cancerous prostate (from 34.7 to 722 mg/L) varies widely [Table 3].
This can be explained by a dependence of Zn content on many factors, including age, ethnicity, mass of the
gland, presence of benign prostatic hyperplasia, and others. Not all these factors were strictly controlled
in cited studies. Another and, in our opinion, leading cause of interobserver variability was insufficient
quality control of results in these studies. In many reported papers EPF samples were dried at high
temperature or acid digestion. Sample digestion is a critical step in elemental analysis and due to the risk
of contamination and analytes loss contributes to the systematic uncontrolled analysis errors [51-53] . Thus,
when using destructive analytical methods it is necessary to control for the losses of TE, for complete acid
digestion of the sample, and for the contaminations by TE during sample decomposition, which needs
adding some chemicals. It is possible to avoid these not easy procedures using non-destructive methods.
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Therefore, sample-nondestructive technique like Cd radionuclide-induced EDXRF, which was developed
and used by us [54,55] is good alternatives for TE determination in EPF samples.

The Cd radionuclide-induced EDXRF developed to determine TE concentrations in prostate fluid is micro
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method because sample volume 20 μL (one drop) is quite enough for analysis. It is another advantage of the
method. Amount of human prostatic fluid collected by massage of the normal prostate is usually in range
100-500 μL but in a pathological state of gland, particularly after malignant transformation, this amount
[56]
may be significantly lower. Therefore, the micro method of Cd radionuclide-induced EDXRF developed to
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determine TE concentrations in prostate fluid is available for using in clinical studies.

Characteristically, elevated or deficient levels of TE and electrolytes observed in EPF of cancerous prostate
are discussed in terms of their potential role in the initiation, promotion, or inhibition of prostate cancer.
In our opinion, abnormal levels of TE in EPF of cancerous prostate could be the consequence of malignant
transformation. Compared to other fluids of human body, the prostate secretion has higher levels of Rb and
Zn and some other TE. These data suggests that these elements could be involved in functional features
of prostate. The suppressed prostatic function can be both a cause and a consequence of BPH. However,
malignant transformation is accompanied by a loss of tissue-specific functional features, which leads to a
significant reduction in the contents of elements associated with functional characteristics of the human
EPF (Rb and Zn).

Our findings show that concentration of Rb and Zn are significantly lower in EPF of cancerous prostate as
compared to their concentrations in EPF of hyperplastic prostate [Table 4]. Thus, it is plausible to assume
that levels of these trace elements in EPF can be used as tumor markers. However, this subjects needs in
additional studies.

This study has several limitations. Firstly, analytical techniques employed in this study measure only five
TE (Br, Fe, Rb, Sr and Zn) concentrations in EPF. Future studies should be directed toward using other
non-destructive analytical methods which will extend the list of TE investigated in EPF of hyperplastic and
cancerous prostate. Secondly, the sample size of PCa group was relatively small. It was not allow us to carry
out the investigations of TE contents in PCa group using differentials like histological types of tumors, stage
of disease, and dietary habits of healthy persons and patients with PCa. Despite these limitations, this study
provides evidence on cancer-specific Rb and Zn level alteration in EPF and shows the necessity the need to
continue TE research of EPF in prostatic diseases.

In conclusion, in this work, TE measurements were carried out in the EPF samples of hyperplastic and
malignant prostate using non-destructive instrumental EDXRF micro method developed by us. It was shown