Independent prognostic role of p16 expression in lung cancer.

Abstract

The cyclin-dependent kinase p16 (also known as Ink4A, Mts1, Cdkn2, and Cdkn4i) has been proposed as a tumor suppressor gene mapped on chromosome segment 9p21. This study evaluated p16 protein expression in 135 lung cancer specimens and investigated potential genetic alterations occurring in this gene. We found altered p16 immunohistochemical expression to be a frequent event in lung cancer and to be independent of either the histologic type or any other clinical-pathologic feature. Western blot analyses performed on about one third of the specimens correlated highly with these results. In addition, we found p16 immunohistochemical expression to be a favorable prognostic factor in lung cancer in that its reduction or loss correlated with a worse outcome for the patients. Polymerase chain reaction amplification and direct sequencing of p16 exons 1 and 2 revealed no mutations, indicating that p16-altered expression in lung cancer is not necessarily linked to mutational events of these genes. We conclude that p16-altered expression is both an independent and frequent event in lung cancer and may have an important role in tumorigenesis and in malignant progression of a significant proportion of these cancers. However, the actual incidence and relevance of p16 mutations in this neoplasm continues to be debated, and its analysis seems inconclusive. Our results suggest a prognostic role for the immunodetection of this protein on formalin-fixed and paraffin-embedded specimens. They further suggest its routine use in the evaluation of the frequently unpredictable behavior of lung cancer.