Prostate cancer (PCa) is the most frequent malignant tumor in the male population worldwide, and has remained one of the leading causes cancer-associated mortality in men (Bray et al.,2018; Ferlay et al., 2019; Siegel, et al., 2020 & Cimadamore et al., 2021). In East Africa, prostate cancer ranks third in both incidence and mortality, and leads to an estimated 9,000 (9% of all male cancers) cases and 7,300 (8.5% of all male cancer) deaths annually (Ferlay et al., 2011). It is significant to note that PCa incidences increased by 64.5% between 1990 and 2010 (Lozano et al., 2012). In 2019, the prevalence of Pca in Western Kenya was at 7.0% (Macharia et al., 2019; Wambalaba et al., 2019 & Luke, 2019). However, the incidences and the mortalities of the prostate cancer are extremely variable worldwide with higher incidence rate occurring most among the Africa-American Men as compared to the white (Panigrahi et al., 2019). The clinical, natural history and pathological behavior of the disease has also been reported to be variable (Ouattara et al, 2012).
Presently the diagnosis of prostatic cancer relies on histopathological features (Stage and Gleason score) supported by combination of Prostate Specific Antigen (PSA) levels and imaging techniques (Garudadri et al., 2020). However, information such as PSA level, cancer stage, and Gleason score, are limited in their ability to determine the disease severity thus complicating most of the clinical decisions (Nayaran et al., 2017). Both PSA and Gleason score are not able to clearly distinguish between indolent and aggressive cancers since tumors with similar histological patterns may have different clinical outcome (Shen and Abate, 2010; Squire et al., 2011 and Schoenborn et al., 2013). This has led to overtreatment and unnecessary biopsies in some cases. PSA also often fails to indicate accurately which patients are responding to a given treatment and is sometimes decreased or increased in higher grade or metastatic tumors. As a biomarker PSA lacks specificity and sensitivity (Epstein et al., 2014 & Romero et al., 2014). Due to increased number of specimens with limited number of suspicious glands and minimal atypia (Magi-Galluzzi, 2018), histomorphological findings in the biopsied tissues sometimes are difficult to report. Distinguishing between aggressive and indolent tumors is a major challenge (Sequeiros et al., 2013). Moreover, differentiating between high-grade urothelial carcinoma (UC) and high-grade Prostate adenocarcinoma (PAC) is frequently a diagnostic and prognostic challenge. According to recent European guidelines, PCa validated biomarkers are urgently needed for guiding the pre-treatment decision processes (Mottet et al., 2017). These scenarios can be improved by using Prostate specific and sensitive immunohistochemical biomarkers, which would adjunct PSA levels and help the pathologist to make much more accurate differential diagnosis.
Basal cell markers (high molecular weight cytokeratins, p63, CK5/6) and α-methylacyl-CoA racemase (AMACR) are presently in use for confirmation malignancy. Prostate-specific antigen (PSA), prostate-specific acid phosphatase (PSAP), and prostate-specific membrane antigen (PSMA) are used to confirm the prostatic origin of the tumor (Adisa et al., 2015 & Kuroda, 2014). Other innovative prostate cancer diagnostic biomarkers include, 4K Score, a Kallikrein markers (Vickers et al., 2010), DNA (hyper) Methylation via Confirm MDXR (Chan et al., 2003), and prostate cancer specific Antigen 3 which measures PCA3 mRNA in first void and post DRE urine (Wei et al., 2017). Although most the prostate markers show excellent specificity, the sensitivity and percentage positivity vary (Chuang et al., 2007).
Prostein (also known as prostate cancer-associated protein 6 / P501S / SLC45A3) is a protein present in the Golgi apparatus of benign and malignant prostatic glandular epithelium. It is encoded by the Solute carrier family 45, member 3 (SLC45A3) gene, an androgen-regulated gene and a prostate specific marker expressed in prostatic glandular cells (Xu et al., 2001). It shows perinuclear cytoplasmic localization in immunohistochemical experiments (Xu et al., 2001; Sheridan et al., 2007). Because it is highly specific for prostate glandular cells, this target is useful for differentiating prostatic metastases from other carcinomas such as urothelial carcinomas or colorectal carcinomas (Xu et al., 2001; Lane et al., 2008; Chuang et al., 2007; Sheridan et al., 2007). Although it may show diminished expression in some aggressive prostate cancers, this target is sometimes expressed in PSA-negative prostate carcinomas, and these two targets used in combination can lead to increased sensitivity in the identification of prostate cancer metastases (Perner et al., 2013; Sheridan et al., 2007). Most cohorts for evaluation of the current diagnostic biomarkers are restricted to the Caucasian Population with little or no representation of other geographic, ethnic population and then directly applied in general way to other population irrespective of their genetic variability (Narayan et al., 2017).
Since prostate cancer is highly heterogeneous and its incidence and mortality vary strikingly among ethnic, racial, and national groups and this is an area worth exploring. native black African patients. There have been no reported studies on manual immunohistochemical diagnostic utility of Prostein in detection of prostate cancer among the African populations. The current study aims to evaluate manual immunohistochemical expression levels of Prostein, P501s, in archived formalin fixed paraffin embedded (FFPE) prostatic core biopsy specimens consecutively collected between January 2018 and May 2021 from prostate cancer patients in Western Kenya.