Frequency of the TP53 Codon 47 and Codon 72 polymorphisms in HIV infected women with histologically confirmed cervical and vulvar pre cancer and invasive cancer reporting at an HIV clinic in Harare, Zimbabwe

Abstract

Cervical cancer is the most common cancer in Zimbabwean women as well as the leading cause of female cancer deaths. There has been an increase in the cervical cancer incidence of Zimbabwe from 56.2 % reported in 2012 to 62.3 % reported in 2019. Genetic changes in somatic cells have been implicated in the etiology of cervical cancer. Tumour suppressor genes have been reported to play a role in both risk to carcinogenesis and development of cancer. More than 50% of human cancers are a result of somatic mutations in the TP53 gene, a major tumor suppressor gene. TP53 plays a crucial role in preventing tumor development by ensuring genomic stability and inhibition of angiogenesis. Codon 72 (rs1042522) is the most common polymorphism of TP53 which has been reported to have a genetic link with cancer susceptibility including cervical and vulvar cancer. Codon 47 (rs1800371) is a polymorphism restricted to African descendent populations with limited studies reported on its association with cancer susceptibility. The aim of this study was to determine the prevalence of TP53 codon 47 and codon 72 polymorphisms in HIV infected women with histologically confirmed cervical and vulvar pre-cancerous lesions and invasive cancer. A cross sectional study that enrolled adult women (aged 18 above) from a cervical cancer screening clinic in Harare was performed. Ethical clearance was obtained from the Medical Research Council of Zimbabwe (Ref: MRCZ/B/1782). Upon giving informed consent, eighty-nine cervical and thirteen vulvar formalin fixed paraffin embedded tissue blocks were retrieved from three different clinical laboratories for analysis. Demographic data retrieved from medical records included age, HIV status, stage of cervical precancer and invasive cancer diagnosis. Typing of human papillomavirus using isothermal amplification of the L1 gene region was done using the ATILA Biosystems Genotyping Fluorescent High-Risk HPV Detection assay, according to manufacturer’s instructions. Genotyping for TP53 exon 4 codon 72 c.215C>G (rs1042522) and codon 47 c.139C>T (rs1800371) was done using polymerase chain reaction (PCR) and Sanger sequencing. Descriptive statistics of variables such as age, HPV type was done using Graph Pad Prism whilst prevalence of codons 47 and 72 was done by simple enumeration. Bivariate analysis was used to investigate any significant (p>0.05) association of clinical data (age and diagnosis) with the genetic variants within the study population. The mean age of the women was 43 years (SD ± 9) and the ages were ranging from 26 to 64 years. The most common diagnosed stage in cervical patients was cervical intraepithelial neoplasia (CIN) 3 with a frequency of 82% (73/89) and vulvar intraepithelial neoplasia (VIN) 3 in 84.6% (11/13) of the vulvar patients. HPV prevalence was 74.7% (65/87) in cervical samples and 92.3% (12/13) in vulvar samples. The most common HPV genotype detected in both cervical and vulvar samples was HPV 16. Forty percent of the study participants had multiple genotypic HPV infections. The frequencies of CC, CG, GG genotypes of codon 72 were reported as 43.5%, 44.9%, and 11.6% respectively for cervical patients and 50%, 41.7% and 8.3% respectively for vulvar patients. The frequency of CC and CT genotypes of codon 47 were reported as 94.2% and 5.8% respectively in cervical patients and 91.7% and 8.3% respectively in vulvar patients. No significant association was observed between TP53 codon 47 and codon 72 genotypes with HPV genotypes as well as age of patients with either HPV genotypes nor histological diagnosis of premalignant lesions and invasive cancer. The study shows that codon 47 polymorphism is restricted to African descendent populations. The prevalence of codon 47 and 72 polymorphism in the study cohort was 6.2% and 55.6% respectively. To the best of my knowledge, this is the first Zimbabwean study to report on the prevalence of TP53 codon 47 polymorphism in cervical and vulvar tissues.