Cancer Genetics and Cytogenetics 122 (2000) 121–123 0165-4608/00/$ – see front matter © 2000 Elsevier Science Inc. All rights reserved. PII: S0165-4608(00)00286-7 Sister chromatid exchanges in peripheral lymphocytes from women with carcinoma of the uterine cervix Elva I. Cortés-Gutiérrez*, Ricardo M. Cerda-Flores, Carlos H. Leal-Garza Division de Genética, Centro de Investigación Biomédica del Noreste, Instituto Mexicano del Seguro Social, 2 de Abril y San Luis Potosi, Colonia Independencia, 64720 Monterrey, N.L., México Received 6 March 2000; received in revised form 27 April 2000; accepted 3 May 2000 Abstract Sister chromatid exchanges (SCE) are reciprocal exchanges between sister chromatids. It has been reported that in patients with cervical cancer, the frequency of SCE in peripheral lymphocytes is significantly higher than that in normal individuals; however, other studies have shown no signifi- cant difference. The aim of this unmatched case-control study was to compare the mean number of SCE per metaphase in lymphocytes from women with and without carcinoma of the cervix uteri. The SCE specimens were prepared by the fluorescence plus giemsa technique in peripheral lymphocytes from 28 women with carcinoma of cervix uteri and 28 controls. The mean number of SCE per metaphase in women with carcinoma of cervix uteri (7.80  1.05) was higher than the control group (6.98  1.13) (P  0.05; t-test). This study had a statistical power of 0.80 and an al- pha value of 0.05. This finding suggests that an increased number of SCE in peripheral lympho- cytes is associated with cervical cancer. We consider that the lack of reported association of SCE and cervical cancer might be attributed to the none determination of the statistical power and sample size. © 2000 Elsevier Science Inc. All rights reserved. 1. Introduction Cervical cancer represents the second most common malig- nant neoplasia in women worldwide. In Mexico, cervical cancer is the most common female malignancy. Therefore, it is neces- sary to establish early diagnostic and prognostic methods [1]. Sister chromatid exchanges (SCE) are reciprocal exchanges between sister chromatids. They are generally visualized by ex- posing cells (in vitro or in vivo) to 5-bromodeoxyuridine (BrdU) for two cell cycles, allowing subsequent differential staining of sister chromatids. Exchanges are detected at switches in stained regions between sister chromatids. The molecular mechanisms of SCE are not known, but they occur after exposure to many genotoxic agents and are believed to indicate DNA damage [2]. The SCE phenomenon is widely used as a reliable indica- tor of chromosome (DNA) instability [3], and has been sug- gested as a preclinical marker for the breast cancer gene [4]. The SCE test in cultured lymphocytes for evaluating the genomic damage in patients with cervical carcinoma is more practical than in solid tumors due to the difficulties in obtaining surgical specimens. The use of lymphocytes is based on the assumption that there should be an association between the extent of chromosomal damage in lymphocytes and in tumor cells [5]. A significant increase of the number of SCEs has been reported previously in patients with cancer of the uterine cervix [6–11]; however, other studies have not shown sig- nificant differences [12]. We consider that the inconsistency in these results might be attributed to the low statistical power in the experimental designs. Statistical power is a measure of the extent to which a study is capable of discerning differences or associations that exist within the population under investigation, and is of critical importance whenever a hypothesis is statistically tested. Conventionally, studies should reach a power level of 0.8, such that four times out of five a false null hypothe- sis will be rejected by a study. The easiest way to increase statistical power is by increasing sample size [13]. The aim of this unmatched case-control study was to de- termine any possible association between the mean number of SCE per metaphase in women with and without carci- noma of cervix uteri. 2. Materials and methods 2.1. Studied population Data analyzed in this research were collected at the Hos- pital de Ginecologia y Obstetricia del Instituto Mexicano * Corresponding author. Centro de Investigación Biomédica del Nor- este, IMSS, Administración de Correos 4, Apartado Postal 20, 64720 Monterrey, N.L., México. FAX: +52-8-190-40-35. E-mail address: elvairenecortes@hotmail.com (E.I. Cortés-Gutiérrez).