Loss of Heterozygosity for a Chromosome 3 Sequence Presumably at 3p21 in Small Cell Lung Cancer Hans Mooibroek, Jan Osinga, Pieter E. Postmus, Ben Carritt, and Charles H.C.M. Buys ABSTRACT: A recombinant DNA fragment detecting a chromosome #3 restriction fragment length polymorphism presumably at p21 was hybridized to HindlII-digested DNA isolated from the leukocytes of 12 patients of small cell lung cancer. Four of them appeared to be heterozygous. Analysis of tumor material from these four patients revealed homozygosity for either one or the other restriction fragment in every case. Our findings suggest the presence on the short arm of chromosome #3 of a recessive mutant cancer gene contributing to the development of small cell lung cancer. INTRODUCTION Deletions of a varying length of the short arm of chromosome #3 were found upon cytogenetic analysis of a number of small cell lung cancer (SCLC) cell lines, short- term cultures of tumor cells, and a SCLC bone marrow preparation [1]. We con- firmed the frequent occurrence of such deletions in a chromosome analysis of three SCLC cell lines and defined p21-p23 as the shortest region of overlap [2, 3]. The human DNA clone ~,Ch4A-H3, previously mapped to lp by in situ hybridization [4, 5], has recently been shown to originate from chromosome #3. This explains the clustering of grains after in situ hybridization not only over lp36, but also to a significant degree over 3p21 [5]. This clone, and its subclone H3H2, detect restric- tion fragment length polymorphisms on both chromosomes #1 and #3 [6,7], that for chromosome #3 being presumably in the region 3p21. H3H2, therefore, was used as a probe to detect possible deletions of 3p21 directly into DNA from tumors of SCLC patients. MATERIALS AND METHODS Leukocytes were recovered from samples of whole blood after osmotic lysis of erythrocytes and platelets by ammonium chloride [8]. High molecular weight DNA was obtained by overnight incubation at 37°C in 10 mM Tris-HC1, pH 8.0, 100 mM From the Departmentsof Human Genetics (H. M., J. O., C. H. C. M. B.) and PulmonaryDiseases (P. E. P.), State Universityof Groningen, The Netherlands, and the MRC Human BiochemicalGenetics Unit (B. C.), University College,London,England. Address requests for reprints to Dr. C. H. C. M. Buys, Department of Human Genetics, State University of Groningen, Antonius Deusinglaan 4, NL 9713 AW Groningen, The Netherlands. Received September 9, 1986; accepted November 25, 1986. 361 © 1987 Elsevier SciencePublishingCo., Inc. Cancer Genet Cytogenet27:361-365 (1987) 52 Vanderbilt Ave., New York, NY 10017 0165-4608/87/$03.50