0165-4608/00/$–see front matter PII S0165-4608(99)00236-8 Cancer Genet Cytogenet 119:83–93 (2000)  2000 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010 LEAD ARTICLE Aneuploidy Precedes and Segregates with Chemical Carcinogenesis Peter Duesberg, Ruhong Li, David Rasnick, Charlotte Rausch, Andreas Willer, Alwin Kraemer, George Yerganian, and Ruediger Hehlmann ABSTRACT: A century ago, Boveri proposed that cancer is caused by aneuploidy, an abnormal bal- ance of chromosomes, because aneuploidy correlates with cancer and because experimental aneu- ploidy generates “pathological” phenotypes. Half a century later, when cancers were found to be non- clonal for aneuploidy, but clonal for somatic gene mutations, this hypothesis was abandoned. As a result, aneuploidy is now generally viewed as a consequence, and mutated genes as a cause of cancer. However, we have recently proposed a two-stage mechanism of carcinogenesis that resolves the dis- crepancy between clonal mutation and nonclonal karyotypes. The proposal is as follows: in stage 1, a carcinogen “initiates” carcinogenesis by generating a preneoplastic aneuploidy; in stage 2, aneuploidy causes asymmetric mitosis because it biases balance-sensitive spindle and chromosomal proteins and alters centrosomes both numerically and structurally (in proportion to the degree of aneuploidy). Therefore, the karyotype of an initiated cell evolves autocatalytically, generating ever-new chromosome combinations, including neoplastic ones. Accordingly, the heterogeneous karyotypes of “clonal” can- cers are an inevitable consequence of the karyotypic instability of aneuploid cells. The notorious long latent periods, of months to decades, from carcinogen to carcinogenesis, would reflect the low probabil- ity of evolving by chance karyotypes that compete favorably with normal cells, in principle analagous to natural evolution. Here, we have confirmed experimentally five predictions of the aneuploidy hypothesis: (1) the carcinogens dimethylbenzanthracene and cytosine arabinoside induced aneuploidy in a fraction of treated Chinese hamster embryo cells; (2) aneuploidy preceded malignant transforma- tion; (3) transformation of carcinogen-treated cells occurred only months after carcinogen treatment, i.e., autocatalytically; (4) preneoplastic aneuploidy segregated with malignant transformation in vitro and with 14 of 14 tumors in animals; and (5) karyotypes of tumors were heterogeneous. We conclude that, with the carcinogens studied, aneuploidy precedes cancer and is necessary for carcinogenesis. © 2000 Elsevier Science Inc. All rights reserved. INTRODUCTION Over a century ago, asymmetric mitoses, which generate an abnormal balance of chromosomes or aneuploidy, were first discovered in epithelial cancer cells by Hansemann [1]. At about the same time, aneuploidy was shown exper- imentally to cause “pathological, lethal, and tumor-like” phenotypes in developing sea urchin embryos by Boveri [2]. On this basis, aneuploidy was proposed to cause can- cer originally by Hansemann [1] and Boveri [2, 3] and then by others up to the 1960s [4–7]. Since the 1960s, however, the aneuploidy-cancer hy- pothesis has been abandoned by many cancer researchers in favor of the somatic gene mutation hypothesis, prima- rily because the cells of virtually all cancers were found to be highly heterogeneous, i.e. nonclonal, with regard to aneuploidy [8–13]. In the meantime, many cancers were found to be clonal with regard to one of many kinds of so- matic gene mutations [14–18], including those caused by reciprocal chromosome translocations [19–21]. In view of the clonality of the gene mutations [14, 15], the nonclonal From the Department of Molecular and Cell Biology, Univer- sity of California at Berkeley (P. D., R. L., D. R.), Berkeley, Califor- nia, USA; the III Medizinische Klinik Mannheim of the University of Heidelberg (P. D., C. R., A. W., A. K., R. H.), Mannheim, Ger- many; Cytogen Research & Development (G. Y.), Boston, Massa- chusetts, USA; and Foster Research Laboratory, Brandeis University (G. Y.), Waltham, Massachusetts, USA. Address correspondence to: Dr. P. Duesberg, University of Cal- ifornia at Berkeley, Department of Molecular and Cell Biology, #3206, Room 126, 229 Stanley Hall, Berkeley, CA 94720-3026. Received October 4, 1999; accepted November 2, 1999.