Deletion Mapping of the Tumor Suppressor Locus Involved in Colorectal Cancer on Chromosome Band 8p21 Florence Lerebours, 1 Sylviane Olschwang, 1,10 * Be ´ ne ´ dicte Thuille, 1 Annette Schmitz, 2 Pierre Fouchet, 2 Pierre Laurent-Puig, 1 Franc ¸ oise Boman, 3 Jean-Franc ¸ ois Fle ´ jou, 4 Genevie ` ve Monges, 5 Franc ¸ ois Paraf, 6 Pierre Bedossa, 7 Jean-Christophe Sabourin, 8 Re ´ my-Jacques Salmon, 9 Rolland Parc, 10 and Gilles Thomas 1,10 1 INSERM U434 Paris, France 2 DSV/DRR CEA, Fontenay Aux Roses, France 3 CHU Brabois, Vandœuvre, France 4 CHU Beaujon, Clichy, France 5 Institut Paoli-Calmettes, Marseille, France 6 CHU Broussais, Paris, France 7 CHU Bice ˆtre, Le Kremlin-Bice ˆtre, France 8 Institut Gustave Roussy, Villejuif, France 9 Institut Curie, Paris, France 10 CHU Saint-Antoine, Paris, France Several somatic genetic alterations have been described in colorectal carcinoma (CRC). Recurrent chromosomal deletions have suggested the presence of tumor suppressor genes (TSG) specifically involved in colorectal carcinogenesis. For one of them, two non-overlapping regions have been proposed on the short arm of chromosome 8, encompassing the LPL and NEFL genes. The short arm of chromosome 8 has been extensively studied in colorectal cancer and in other cancer types. Both regions have been reported as candidate loci for a TSG. In order to delineate a reliable region of deletional overlap on chromosome arm 8p in CRC, a series of 365 CRC samples was selected for the absence of microsatellite instability (RER, replication error); tumor and normal matched DNAs were studied for 54 microsatellite polymorphisms distributed on 8p using multiplex-PCR amplification. After purification of tumor nuclei by flow cytometry based on either the abnormal DNA index or the presence of a high expression of cytokeratin, complete allelic losses on 8p were observed in 48% of cases. Measurement of the DNA index showed that 88% of RER tumors were hyperploid. Complete allelic losses of only part of the short arm were observed on 26 occasions. These data allowed us to define a 1 cM interval of common deletion, flanked by the loci D8S1771 and NEFL, where a putative TSG may be localized. Genes Chromosomes Cancer 25:147–153, 1999.  1999 Wiley-Liss, Inc. INTRODUCTION Since the initial work of Cavenee et al. (1983), the comparative analysis of matched constitutional and tumor DNAs has provided a large amount of information. When applied to colorectal cancer (CRC), it has led to the identification of a subgroup of tumors that are deficient in the mismatch repair pathway, thus leading to the identification of the genes involved in hereditary nonpolyposis colorec- tal cancer. This group, which amounts to approxi- mately 15% of sporadic CRC, is clearly distinct from the major group that is proficient in DNA mismatch repair, but which demonstrates frequent losses of alleles (LOH). Recurrent allelic imbalance in tumor DNA has been used as an indication of the presence of tumor suppressor genes (TSGs) in the corresponding chromosome segment. Indeed, in this type of tumor investigation of LOH has led to the identification of a major tumor suppressor gene, APC (5q21) (Nishisho et al., 1991; Groden et al., 1995), to the recognition of the frequent involve- ment of TP53 (17p13.1) in human cancer (Baker at al., 1989, 1990), and to the identification of three genes on the long arm of chromosome 18, DCC, DPC4, and SMAD2, which are being investigated for their implication in colorectal tumorigenesis (Cho et al., 1994; Eppert et al, 1996; Hahn et al., 1996). In the first whole genome search for LOH in CRC, Vogelstein et al. (1989) used markers located on all non-acrocentric chromosome segments and observed that the chromosome segment that dem- onstrated the highest allelic imbalance frequency, after 17p, 18q, and 5q, was 8p. This observation was Supported by: LNCC Comite ´ de Paris, ARC, FEGEFLUC and MESR., fellowship from LNCC (F.L.). *Correspondence to: Sylviane Olschwang, INSERM U434, Fonda- tion Jean Dausset – C.E.P.H., 27, rue Juliette Dodu, 75010 Paris, France. E-mail: olschwang@cephb.fr Received 19 October 1998; Accepted 12 January 1999 GENES, CHROMOSOMES & CANCER 25:147–153 (1999)  1999 Wiley-Liss, Inc.