A Large 6 q Deletion Is a Common Cytogenetic Alteration in Fibroadenomas , Premalignant Lesions , and Carcinomas of the Breast 1

To assess whether early breast lesions are the precursors of invasive carcinomas, three classes of breast lesions, namely benign tumors (including fibroadenomas), putative premalignant lesions (including cases of atypical hyperplasia), and invasive carcinomas, were compared at the cytogenetic and molecular cytogenetic levels. Genetic relatedness was clearly demonstrated by the sharing of several anomalies, among which 6q deletions outnumbered all of the other alterations detected. Indeed, deletions of the long arm of chromosome 6, most likely occurring in epithelial cells, were present in 83.9% of benign breast tumors, 64% of putative premalignant lesions, and 77.4% of analyzable carcinomas. Furthermore, the interval between 6q24 and qter appeared to be the common region of deletion in all three classes of breast lesions, whereas the minimal common region of deletion was 6q27-qter. Interestingly, the latter region was reported previously to be deleted in benign ovarian tumors and recently found to harbor a gene (SEN6) that is important for SV40-mediated immortalization of human cells. INTRODUCTION Breast CA is among the most common and lethal malignancies in women in western countries. Because this malignancy is very common and difficult to treat, there is growing interest in studying early premalignant changes of invasive breast cancer to prevent and control this disease. PBLs constitute a large group of abnormalities, the nature and contribution to overt CA of which are not well established yet. The most convincing evidence favoring a causal relationship between these two pathological entities (putative precursors and invasive CA) is mainly derived from epidemiological studies: women with PBLs such as usual hyperplasia, atypical hyperplasia, andin situ CA have approximately 2-, 4-, and 10-fold increased relative risks, respectively, of eventually developing invasive breast cancer (1–4). Clearly, the presence of genetic abnormalities in PBLs would implicate these lesions as potential precursors of breast cancers and could shed light on genetic abnormalities that may play a role in early breast tumorigenesis. Recent insights concerning a probable common genetic pathway between benign lesions and CAs of the breast were gained from molecular studies employing LOH at 15 polymorphic loci in 399 putative precursor lesions (including UDH, ADH, and ductal CA in situ; Ref. 5). Loss of material from several loci was reported, and more importantly, a sharing of LOH phenotypes between hyperplastic breast disease and synchronous cancer has strengthened the concept that hyperplasias may be precursors of breast cancer (5–7). Among benign lesions of the breast, one of the most common is fibroadenoma, which is considered a neoplasm composed of epithelial and stromal components (8). Women can present with this lesion at any age, but the tumor is most commonly diagnosed when the patients are in their twenties, an age that is very unusual for breast cancer. Perhaps for this reason, fibroadenomas have traditionally been thought to be unrelated to breast cancer. Nevertheless, several investigators have found that women with fibroadenomas, compared with women of similar age in the general population, have two to three times the general risk of breast cancer (9–13). To date, only 33 fibroadenomas with clonal chromosome aberrations have been reported (14–21). In all cases, the cytogenetic analysis was performed using short-term cultures, and Received 6/28/99; revised 9/29/99; accepted 10/15/99. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisementin accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by Grants from “Ministero Dell’Universita ` e della Ricerca Scientifica e Tecnologicala,” University of Pavia. R. T. was supported by a grant from Associazione Italiana per la Ricerca sul Cancro. 2 To whom requests for reprints should be addressed, at Dipartimento di Biologia Strutturale e Funzionale, Via J. H. Dunant 3, 21100 Varese, Italy. Phone: 39-0332-421514; Fax: 39-0332-421-500. 3 The abbreviations used are: CA, carcinoma; ADH, atypical ductal hyperplasia; BBT, benign breast tumor; BL, breast lesion; cDCIS, comedo ductal carcinoma in situ; ncDCIS, noncomedo ductal carcinoma in situ; FISH, fluorescencein situ hybridization; LOH, loss of heterozygosity; PBL, proliferative breast lesion; PPL, putative premalignant lesion; UDH, usual ductal hyperplasia; YAC, yeast artificial chromosome. 1422Vol. 6, 1422–1431, April 2000 Clinical Cancer Research Research. on August 29, 2017. © 2000 American Association for Cancer clincancerres.aacrjournals. org Downloaded from the origin (epithelial or stromal) of the clonal abnormalities was not evaluated. No fibroadenoma-specific aberrations have emerged from the reported studies, although rearrangements of chromosomes 1, 6, and 3 have been repeatedly involved in clonal changes (14, 19–21). Numerical alterations and, in particular, monosomy for chromosome 6 and trisomy for chromosomes 4, 7, and 20 were also reported (14–21). However, studies using molecular approaches failed to detect alterations in this class of benign neoplasms (22). To provide additional evidence for a genetic relatedness between putative precursor lesions and breast CAs, we performed cytogenetic and FISH analyses on fibroadenomas, hyperproliferative lesions, and breast cancers. Additionally, we also studied a series of cases in which a double sampling in morphological different areas (cancerous and noncancerous) was performed. All cytogenetic results described in this report were obtained following direct harvesting and short-term incubation of the tumor cells. We found that this methodological approach is the most appropriate to study the chromosome pattern of solid tumors because it avoids selection biases due to culturing (23, 24). Among several cytogenetic changes detected in all three classes of BLs, the most frequent lesions involved chromosome 6q. This finding, besides adding further evidence for a progression mechanism reminiscent of that identified in colon cancer, suggests that alterations of genes located in 6q are among of the earliest events in the pathogenesis of breast cancer. MATERIALS AND METHODS