A Direct Cytogenetic Technique for Mouse Skin Carcinomas and Papillomas Claudio M. Aldaz, Claudio J. Conti, Andres J. P. Klein-Szanto, and Thomas J. Slaga ABSTRACT: A method was developed for obtaining direct chromosome preparations from SENCAR mouse skin tumors induced by chemical carcinogenesis protocols. Papillomas and squamous cell carcinomas were mechanically dispersed immediately after resection and were placed in a modified Hanks' solution with collagenase, trypsin, hyaluranidase, bovine albumin, and Colcemid. Total exposure to Calcemid did not exceed 1 hr. Metaphases were obtained in 100% of the analyzed specimens, allowing chromosome counting screening for double min- utes and, in 50% of the cases, useful G-banded slides. The technique described has produced, for this type of tumor, a higher number of successful G-banded preparations than other pre- viously reported methods for solid tumors, This procedure may be applicable for the study of human solid tumors that are histologically similar to our murine model, such as squamous cell carcinoma of cervix or lung. INTRODUCTION The mouse skin model is one of the best systems for studying the multistep nature of carcinogenesis [1]. However, cytogenetic studies have not been reported in this model, as the detailed chromosomal analysis of solid tumors is known to be one of the most discouraging tasks in cytogenetics [2-5]. The importance of developing reliable methods for studying epidermal tumors from fresh preparations, without using cell culture techniques, cannot be stressed enough. Relying on the cell culture step can have serious drawbacks, such as failure to establish cell lines or eventual in vitro induction of structural and numerical karyotype alterations [2]. In this article we describe a simple and reliable method for obtaining direct chro- mosome preparations from mouse skin papillomas and squamous cell carcinomas, in which high percentage of the metaphases are suitable for analysis with G-band- ing techniques. From the University of Texas System Cancer Center, Science Park-Research Division, Smithville, TX. Address requests for reprints to Dr. Claudio J. Conti, University of Texas System Cancer Center, Science Park-Research Division, P.O. Box 389, Smithville, TX 78957. Part of this investigation was presented at the First International Conference on Chromo- somes in Solid Tumors, March 1985, Tucson,AZ. Received March 28, 1985; accepted May 7, 1985. 223 © 1986 Elsevier Science Publishing Co., Inc. Cancer Genet Cytogenet 20:223-229 (1986) 52 Vanderbilt Ave., New York, NY 10017 0165-4608/86/$03.50