Prostate carcinoma is one of the leading causes of male cancers. Major risk factors include advancing age and family history and lifestyle, and a Western diet rich in saturated fat and low in fiber and obesity with related disorders such as insulin resistance and metabolic syndrome. Healthy weight and diet rich in soy isoflavonoids are the most relevant protective factors. Screening for genetic risks is useful for the detection of high-risk patients who would benefit from a biopsy. The underlying mechanisms that link prostate cancer to obesity include high levels of and insulin-like growth factor I (IGF-I) and sex steroids due to their anabolic properties. Additional theories include chronic inflammation, oxidative stress, hypoxia, and immune system changes. Prostate-Specific Antigen (PSA) is still a useful tool; however, its results need to be interpreted in the context of other risks and clinical presentation. Biopsy shall be performed where clinically justified. Androgen metabolism is essential for the understanding of the pathophysiology of the disease and the development of appropriate drug targets. Blocking the intra-tumor synthesis of androgens is critical to the success of advanced prostate cancers.
Prostate cancer
Prostate carcinoma is the second most common of all cancers and the sixth leading cause of male cancer deaths. The highest prevalence of prostate cancer is among men, Europe, North America, Australia, and New Zealand, whilst men in Southeast Asia are affected the least. The risk of prostate cancer increases with age. Other risk factors include family history, genetics, obesity, diet, medications, infections, and sexual habits. Clinical presentation includes frequent urination, hematuria and dysuria, lower limb lymphedema, and bone tenderness. Prostate carcinoma is locally invasive and spreads into the bone, especially the pelvis and the spine. Treatment involves the combination of surgery, radiation therapy, hormonal treatment, and chemotherapy. Many men who die of other causes have prostate cancer detected at autopsy that was undetected during their lifetime (Mustafa et al., 2016).
Pathophysiology: Risk factors
Advancing age is the most important risk factor for the development of prostate cancer. Approximately 60% of all cases of prostate cancer are diagnosed in men over65 years of age. The disease is associated with a Western lifestyle, fat-rich diet, and obesity. African-Americans are at higher risk of developing prostate cancer and are also 2.4 times more likely to die from the disease (Bashir, 2015). Prostate cancer is one of the most heritable cancers, with about 42% of the risk attributable to genetics. However, family cancer history is not always known to the patient and the clinician. Alternative methods of calculation of genetic risk score (GRS) include single-nucleotide polymorphisms carried by the individual (Helfand, 2016).
Obesity is a significant contributor to cancer deaths, second only to smoking. It is estimated that obesity increases the risk of cancer by up to 20%. Endometrial and postmenopausal breast cancer show the highest association between obesity and malignancy. Other cancers strongly linked to obesity are esophageal adenocarcinoma, colorectal and renal carcinomas, and prostate cancer.
The underlying mechanisms that link cancer to obesity include insulin, insulin-like growth factor I (IGF-I), and sex steroids. Additional theories include chronic inflammation, oxidative stress, migrating adipose stromal cells, obesity-induced hypoxia, and a functional defect of immune function (De Pergola, & Silvestris, 2013).
The lifestyle that leads to cardiovascular disease also increases the risk of prostate cancer. Various dietary supplements such as selenium and vitamin E were tested for their ability to prevent prostate cancer. These supplements were not effective in lowering the risk of cardiovascular disease or cancers. Drugs that promote cardiovascular health, such as statins, metformin, and aspirin, are also effective in the prevention of prostate cancer. These medications are beneficial as auxiliary agents in the management of aggressive prostate cancer. In two large trials, Prostate Cancer Prevention Trial (PCPT) with finasteride and REduction by DUtasteride of Prostate Cancer Events (REDUCE) failed to show any benefit of these medications on the reduction of the incidence of prostate cancer. However, the trials clearly showed how the risk of prostate cancer relates to the risk of death from cardiovascular disease: of the 18.000 men who participated in the PCPT trial, five men on finasteride, and five on placebo died of prostate cancer. In contrast, 1,123 died from other causes, mostly cardiovascular (Moyad, & Vogelzang, 2014). Fibrates, a commonly used medication used as a cholesterol-lowering agent, showed no effect on the prevention of prostate cancer (Bonovas, Nikolopoulos, & Bagos, 2012).
Isoflavones such as genistein, daidzein, and biochanin were investigated for their role in the prevention of prostate cancer. The results are conflicting, showing both harmful and positive effects. Soy foods that are rich in genistein are the main component of the Asian diet. The difference in dietary uptake of genistein can likely account for the difference in the prevalence of prostate cancers in Western and Asian populations (Ahmad et al., 2013).
Increased incidence of prostate cancer is associated with prostate inflammation resulting from prostatitis caused by sexually transmitted infections. Chronic inflammation increases the risk of development of many cancers through cell and genome damage, altered cell signaling functions, and promotion of cell replication and angiogenesis. Detection and recall of prostatitis, especially if asymptomatic, are significant limitations of epidemiological studies. In the absence of androgen stimulation, prostate tissue responds by diffuse atrophy. If androgen stimulation is present, however, the tissue responds to inflammation by focal atrophy that is associated with prostate cancer. Epithelial cells within these lesions proliferate extensively and show indications of the high level of oxidative stress. Accumulated genome damage then leads to transformation into cancer cells. Practical experience suggests the contributing role of colonization by Chlamydia trachomatis, Ureaplasma urealyticum, Trichomonas vaginalis, Neisseria gonorrheae, cytomegalovirus infection, and herpes simplex. Both symptomatic and asymptomatic prostatitis increases PSA levels. However, not all types of prostate inflammation increase the risk of prostate cancer in the same manner (Nakai, & Nonomura, 2012).
Sexual activity affects the probability of developing prostate cancer in both protective and deleterious manner. The main mechanisms studied are high androgen status, the risk of sexually transmitted infections, and the retention of carcinogens within prostatic cells. While frequent ejaculation seems to be protective due to the drainage of carcinogenic substances from prostatic acini, high androgen status, and the risk of contracting sexually transmitted diseases, increase the risk. There is an association between a higher number of female sexual partners and the risk of prostate cancer due to the increased risk of sexually transmitted diseases. The protective effect of phosphodiesterase inhibitors for erectile dysfunction is explained by a higher frequency of ejaculation and the ability to retain sexual functions. Homosexuality increases the risk of developing prostate cancer due to a higher risk of HIV infection. Trauma to the prostate during receptive anal intercourse increases the level of prostate-specific antigen (PSA), artificially increasing the diagnosis rates. Physical injury may also lead to a higher risk of prostate cancer (Kotb, Beltagy, Ismail, & Hashad, 2015).
Androgen metabolism is essential for the understanding of the pathophysiology of the disease and the development of therapeutic targets. Adrenal androgens (i.e., dehydroepiandrosterone) are a source for the intratumoral dihydrotestosterone. This production of hormones by the tumor makes certain types of prostate cancer resistant to castration. Prostate cancer changes the expression of steroidogenic enzymes and affects androgen metabolism. Androgen deprivation therapy through surgical or medical castration is the mainstay therapy for advanced prostate cancer. Overexpression of the androgen receptor in tumor tissue contributes to the progression into castration-resistant prostate cancer. Similarly, mutations in the androgen receptor and the synthesis of dihydrotestosterone (DHT) have the same effect. Blocking the intra-tumor synthesis of androgens can be achieved by inhibiting CYP17A1 activity, resulting in suppression of tumor growth. Abiraterone acetate and enzalutamide halt the progression only temporarily. The reason is that the tumor eventually develops resistance to these agents (Chang, Ercole, & Sharifi, 2014).
The extent of contribution of gender to prostate cancer etiology
Dehydroepiandrosterone (DHEA), available in the bloodstream, is converted first to androstenedione and then to DHT. The first step of adrenal androgen metabolism is catalyzed by 3b-hydroxysteroid dehydrogenase and D5 -D4 isomerase. The conversion to DHT requires 17bHSD and steroid-5a-reductase. Alternatively, adrenal androstenedione is converted to 5a-androstanedione and then to DHT (the ‘5a-dione pathway’). The majority of castration-resistant prostate cancers use the alternative pathway, thus avoiding the need for testosterone. Metabolism of androgens in tumorous tissue and gene expression has been studied extensively as part of screening for new potential drug targets. In clinical oncology, the treatment of individual patients depends on tumor biology and underlying genetic defect (Chang, Ercole, & Sharifi, 2014).
Androgens, however, only become the key factor in prostate cancer pathogenesis in the very last stage. The relevant risk factors are advancing age, obesity, insulin resistance, metabolic syndrome, and chronic inflammation. These factors are gender-neutral and can be influenced by lifestyle.
Prevention
Treatment of prostatitis with antibiotics can reduce the likelihood of the development of prostate cancer by reducing chronic inflammation. Treating prostate infection and targeting dietary habits may be the most important way of prostate cancer prevention (Nakai, & Nonomura, 2012). Antidiabetic therapy is essential to the prevention of prostate cancer. The pathophysiologic effect of insulin and insulin resistance have a critical influence on its development. Insulin and drugs that promote the secretion of insulin, such as sulfonylureas, increase the risk of cancer-related mortality. On the other hand, metformin and thiazolidinediones reduce this risk (Hitron, Adams, Talbert, & Steinke, 2012). A healthy lifestyle, including a diet rich in soy products and low in saturated fat and maintaining a healthy weight, is the most important part of prostate cancer prevention. Diet low in animal fat is also essential to limit the source of prostate inflammation and oxidative stress.
Detection of risk factors
Tests for the early detection of prostate cancer such as the Prostate-Specific Antigen (PSA) and biopsy significantly increased the incidence of prostate cancer. Due to the long latency stage, a positive test does not equal the need for immediate intervention. PSA, although not very specific, is still a valid biomarker useful for monitoring patients under active surveillance, with repeat biopsies as a follow—up (Romero-Otero et al., 2015).
The decision when and how frequently to take bioptic samples depends on various individual risk factors. Indicators relating to obesity currently investigated for cancer risk include body mass index (BMI), waist-to-hip ratio, and waist circumference. Visceral adiposity is associated with a higher risk of cancer than general adiposity. Obesity is the cause of approximately 20% of cancer deaths in women and 14% in men. Some mechanisms are universal; other are more tumor and location-specific. Excess dietary energy and overindulgence in animal fats and alcohol are linked to cancer incidence and tumor progression. The protective effect of energy balance is likely related to the levels of insulin due to its anabolic and antiapoptotic effects, resulting in insulin resistance, increased levels of IGF-I that promote cell growth, and inflammatory biomarkers. Insulin receptors are overexpressed in prostate cancer cells. Obesity leads to oversecretion of proinflammatory molecules. Examples are interleukin-6 (IL-6), tumor necrosis factor-alpha, leptin, resistin, and others. The secretion of beneficial adipokines is lower. An additional effect of obesity includes oxidative stress and immune system alterations (De Pergola, & Silvestris, 2013).
Some of the important gene markers located on chromosome 1 include HPC1, PCAP, and CAPB. Association was found between mutations in the breast cancer predisposition genes (BRCA1 and BRCA2) and increased risk of prostate cancer. Additional regions associated with increased risk of prostate cancer include 1q23, 5q11, 5q35, 6p21, 8q12, 11q13, and 20p11–q11 and the prostate cancer susceptibility gene HOXB13. GCS is a measurement of inherited risk for prostate cancer and is calculated from the cumulative effect of single-gene mutations. GCS is essential information in a clinical decision relating to the timing and frequency of biopsies in addition to family history and other screening tests (Helfand, 2016).
Conclusion
The incidence of prostate cancer increases in the developed world, partially due to advanced screening programs designed to detect prostate cancer in its early stages, and partially due to a strong correlation between cancer and metabolic syndrome. The most relevant risk factors for the development of prostate cancer include advancing age, family history, obesity, insulin resistance, chronic inflammation, including sexually transmitted infections and colonization of prostate by specific pathogens and low sexual activity. In advanced stages, the most relevant mechanism of cancer growth and the spread becomes its acceleration by androgens. Prevention strategies include lifestyle changes and active surveillance of high-risk groups. The timing of biopsies and their frequency remains a challenge. Indicators of high-risk include BMI, waist-to-hip ratio, genetic risk score, and inflammation markers.