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Mentions: We grouped together prospective and retrospective data previously obtained from histologic and clinical records at the tertiary referral or university teaching hospitals serving the six Nigerian geopolitical zones (Figure 1), each of which covers a core state and several peripheral states. The data provided by the teaching hospitals in each of the geopolitical zones and their peripheral states are shown in Table 1. Our study population was broadened because we examined data from two or more such tertiary health institutions in a zone. Because our data embraced all of the geopolitical zones in Nigeria, the information it provides may constitute the most extensive hospital-based prostate cancer incidence report for Nigeria so far. Nonetheless, the present data compensate for the lack of satisfactory prostate cancer incidence data that ought to be coordinated and collated by the Ibadan University College Hospital (UCH) National Headquarters for Cancer Registries in Nigeria. Such data ought to be generated by population-based screening for prostate and other cancers in the presently existing university teaching hospital-based registries at Maiduguri, Zaria, Jos, Kano, Ilorin, Calabar, Enugu, Lagos, and Ife-Ijesha. The data presented in this report were retrieved by researchers from these teaching hospital-based registries, except for the Usman Danfodiyo UCH records, which were obtained from a cancer patient register in the department of histopathology. The histology and cytology specimens21,22 used for some of these studies were obtained from tertiary, secondary, and private hospitals located close to the core tertiary hospital and the surrounding peripheral states, towns, and villages23 within that particular geopolitical zone. In a few surveys of prostate cancer risk from a seldom-screened cohort of the rural population, participants were invited for a health survey after alerting them to the procedures involved, including a blood test and digital rectal examination (DRE) by a local nurse.24 In many of the retrospective studies, information on the age of patients at presentation,21,25–27 histopathological grading, mode of presentation, clinical and biochemical response to chemotherapy, their relative frequencies,28 and the level of prevailing tumor biomarkers were obtained from patient files.29–31 In prospective studies, data were obtained from patients presenting with histologically diagnosed carcinoma of the prostate during the study period.32 Again, in the prospective studies, various patient information was documented including, but not limited to, prevailing biomarker levels such as serum acid phosphatase, DRE, blood electrolyte profile, prostate biopsy, transabdominal ultrasonography, and a survey of the skeleton.32,33 In some of the more recent cases, detection of prostate cancer by prostate-specific antigen (PSA) was preceded by DRE. In most cases, the diagnosis was made on the basis of DRE, an ultrasound scan (which when combined with artificial neural network classification tools enabled encouraging differentiation between cancerous and noncancerous tissue),34 and confirmed by Tru-Cut (UK Medical Limited, Sheffield, UK) prostatic biopsy.21 In certain cases too, the clinical staging of the disease was determined using the tumor, node, metastasis (TNM) system at the time of DRE.29 In others, the prostate was carefully assessed for size, hardness, nodularity fixation, and discomfort.33 Staff at the registries was centrally trained through programs run by the National Headquarters for Cancer Registries in Nigeria and delivered as instructed data items abstracted from pathology reports, medical charts, and questionnaires to treating physicians in order to obtain complete data on therapies. To avoid duplication, all retrieved records were reported to have been double-checked by name and matched with hospital numbers. Cases presented by the reports ranged from 125 to 4686, where large number of cases represented retrospective studies of all malignant diseases studied over a longer period. Age-standardized rates were calculated using Nigerian census figures for the appropriate study periods. The mean sample size for assessment of prostate tumors and benign prostatic hyperplasia was 327 ± 280.12. Studies were variously approved by the research and ethics committees of the tertiary health institutions involved.24
Emergent trends in the reported incidence of prostate cancer in Nigeria
Bottom Line: Our results suggest that prostate cancer occurs at a relatively young age in Nigerians and that hospital-based registry reports may not appropriately reflect the incidence of the disease in Nigeria.Finally, the difference in reported stages of disease found in Nigerians and African-Americans versus Caucasians suggests biological differences in the prognosis.Nigeria may thus typify one of the ancestral populations that harbor inherited genes predisposing African-Americans to high-risk prostate cancer.
Affiliation: Department of Biological Sciences, Clark Atlanta University, Atlanta, GA, USA.
Background: To date there has not been any nationwide age-standardized incidence data reported for prostate cancer in Nigeria. We examined and integrated diverse trends in the age-specific incidence of prostate cancer into a comprehensive trend for Nigeria, and examined how best the existing data could generate a countrywide age-standardized incidence rate for the disease.
Methods: Data were obtained from studies undertaken between 1970 and 2007 in referral hospital-based cancer registries. Records from at least one tertiary hospital in each of the six geopolitical zones of Nigeria were examined retrospectively. Data were also reported for the rural population in cross-sectional prospective studies. Age-standardized incidence rates and the annual incidence of disease were calculated.
Results: Higher incidence rates for prostate cancer during this period were recorded for patients aged 60-69 years and 70-79 years, with a lower incidence rate for patients aged younger than 50 years. An exponential annual incidence rate of disease was observed in the 50-79 year age group and peaked at 70-79 years before dropping again at age 80 years. The results showed metastasis in more than half of these hospital-based prostate tumors.
Conclusion: Our results suggest that prostate cancer occurs at a relatively young age in Nigerians and that hospital-based registry reports may not appropriately reflect the incidence of the disease in Nigeria. A countrywide screening program is urgently needed. Finally, the difference in reported stages of disease found in Nigerians and African-Americans versus Caucasians suggests biological differences in the prognosis. Nigeria may thus typify one of the ancestral populations that harbor inherited genes predisposing African-Americans to high-risk prostate cancer.