The invention concerns compositions and methods for the diagnosis and treatment of neoplastic cell growth and proliferation in mammals, including humans. The invention is based upon the identification of an ADAM8 gene that is amplified in the genome of tumor cells. Such gene amplification is associated with the overexpression of the gene product as compared to normal cells of the same tissue type and contributes to tumorigenesis. Accordingly, the ADAM8 protein encoded by the amplified gene is a useful target for the diagnosis and/or treatment (including prevention) of certain cancers, and acts as a predictor of the prognosis of tumor treatment.