Disruption of the RB pathway and cell‐proliferative activity in non‐small‐cell lung cancers

The pathway consisting of retinoblastoma protein (pRB), cyclin D1 and p16 (RB pathway) which is involved in the phosphorylation of pRB plays an important role in G1/S progression. The disruption of this RB pathway has been reported in several types of human neoplasm. An immunohistochemical study of 101 non‐small‐cell lung cancers (NSCLCs) showed loss of p16 is in 47 tumors (46.5%) and loss of pRB in 42 tumors (41.6%). In 79 of 101 NSCLCs (78.2%), the expression of p16 and pRB was complementary (p < 0.0001). Methylation of the cdkn2 gene was detected in 50% of p16‐negative tumors and in 11% of p16‐positive tumors. Aberrant expression of cyclin D1 was found in 45 tumors (44.5%). The cyclin‐D1‐positive tumors had significantly higher Ki‐67 indices than the cyclin‐D1‐negative tumors irrespective of the tumor p16 or pRB expression. Thus, 91 (90%) of 101 NSCLCs showed disturbed expression of at least 1 of the 3 components of the RB pathway. Our results suggest that the disruption of the RB pathway plays an important role in tumorigenesis in NSCLCs and that increased cyclin‐D1 expression leads to strong proliferative activity which may over‐ride the suppressive effect of p16 and pRB. Int. J. Cancer (Pred. Oncol.) 79:111–115, 1998.© 1998 Wiley‐Liss, Inc.