Genes of the polycomb group function by silencing homeotic selector genes that 
regulate embryogenesis. In mice, downregulation of one of the polycomb genes, 
bmi-1, leads to neurological alterations and severe proliferative defects in 
lymphoid cells, whilst bmi-1 overexpression, together with upregulation of 
myc-1, induces lymphoma. An oncogenic function has been further supported in 
primary fibroblast studies where bmi-1 overexpression induces immortalization 
due to repression of p16/p19ARF, and where together with H-ras, it readily 
transforms MEFs. It was the aim of this study to assess the expression of bmi-1 
in resectable non-small cell lung cancer (NSCLC) in association with p16 and 
p14ARF (=human p19ARF). Tumours (48 resectable NSCLC (32 squamous, 9 adeno-, 2 
large cell, 4 undifferentiated carcinomas and 1 carcinoid); stage I, 29, II, 7, 
III, 12; T1, 18, T2, 30; differentiation: G1 12, G2 19, G3 17) were studied by 
immunohistochemistry for protein expression and by comparative multiplex PCR for 
gene amplification analysis. In tumour-free, normal lung tissue from patients, 
weak - moderate bmi-1 staining was seen in some epithelial cells, lymphocytes, 
glandular cells and in fibroblasts, whereas blood, endothelial, chondrocytes, 
muscle cells and adipocytes did not exhibit any bmi-1 expression. In tumours, 
malignant cells were negative/weakly, moderately and strongly positive in 20, 22 
and 6 cases, respectively. As assessed by multiplex PCR, bmi-1 gene 
amplification was not the reason for high-level bmi-1 expression. Tumours with 
moderate or strong bmi-1 expression were more likely to have low levels of p16 
and p14ARF (P = 0.02). Similarly, tumours negative for both, p16 and p14ARF, 
exhibit moderate-strong bmi-1 staining. 58% of resectable NSCLC exhibit 
moderate-high levels of bmi-1 protein. The inverse correlation of bmi-1 and the 
INK4 locus proteins expression (p16/p14ARF) supports a possible role for bmi-1 
misregulation in lung carcinogenesis.