BACKGROUND: MicroRNA expression is severely disrupted in carcinogenesis, however 
limited evidence is available validating results from cell-line models in human 
clinical cancer specimens. MicroRNA-21 (mir-21) and microRNA-143 (mir-143) have 
previously been identified as significantly deregulated in a range of cancers 
including cervical cancer. Our goal was to investigate the expression patterns 
of several well-studied microRNA species in cervical samples and compare the 
results to cell line samples.
METHODOLOGY/PRINCIPAL FINDINGS: We measured the expression of mir-21 and mir-143 
in 142 formalin-fixed, paraffin embedded (FFPE) cervical biopsy tissue blocks, 
collected from Dantec Oncology Clinic, Dakar, Senegal. MicroRNA expression 
analysis was performed using Taqman-based real-time PCR assays. Protein 
immunohistochemical staining was also performed to investigate target protein 
expression on 72 samples. We found that mir-21 expression increased with 
worsening clinical diagnosis but that mir-143 was not correlated with histology. 
These observations were in stark contrast to previous reports involving cervical 
cancer cell lines in which mir-143 was consistently down-regulated but mir-21 
largely unaffected. We also identified, for the first time, that cytoplasmic 
expression of Programmed Cell Death Protein 4 PDCD4; a known target of mir-21) 
was significantly lower in women with invasive cervical carcinoma (ICC) in 
comparison to those with cervical intraepithelial neoplasia (2-3) or carcinoma 
in situ (CIN2-3/CIS), although there was no significant correlation between 
mir-21 and PDCD4 expression, despite previous studies identifying PDCD4 
transcript as a known mir-21 target.
CONCLUSIONS: Whilst microRNA biomarkers have a number of promising features, 
more studies on expression levels in histologically defined clinical specimens 
are required to investigate clinical relevance of discovery-based studies. 
Mir-21 may be of some utility in predictive screening, given that we observed a 
significant correlation between mir-21 expression level and worsening 
histological diagnosis of cervical cancer.