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From the Molecular Pathology Division,*
Department of
Cellular Pathology, Armed Forces Institute of Pathology, Washington,
D.C.; and the Department of Pathology,
Louisiana State University Medical Center, Shreveport, Louisiana
| Abstract |
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| Introduction |
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The relative risk for the development of cancer associated with specific benign pathological entities has been characterized in epidemiological studies.8,9 The presence of mild sclerosing adenosis, apocrine metaplasia, mild hyperplasia, fibrosis, cysts, or a solitary papilloma carries no increased risk of cancer. Florid or atypical hyperplasia leads to a moderate increase (1.54 times) in the relative risk, and lobular or ductal carcinoma in situ increases the risk for cancer by 810 times. For each of these pathological findings, including those associated with increased cancer risk, it is generally not known whether the abnormal proliferation is an actual precursor of the malignancy or, instead, an indicator of an underlying global pathological process. For example, the identification of lobular carcinoma in situ in one breast is associated with an increased risk of cancer in either breast. Therefore, lobular carcinoma in situ seems to be an indicator for a predilection to develop cancer rather than a direct precursor of the tumor.10-12 The few studies that have analyzed genetic alterations in fibrocystic change have focused largely on atypical ductal hyperplasia; other morphological entities included under this heading have not been well characterized for genetic abnormalities.3,13-15
The purpose of the present study was to characterize the frequency of LOH in the components of fibrocystic change and to begin to address the question of whether benign proliferative lesions can be identified that show evidence for a genetic relationship with a carcinoma in the same breast. In this study, 32 cases of fibrocystic change were studied for LOH at 14 chromosomal loci. Individual foci of epithelial cells, representing normal TDLUs, ductal hyperplasia, adenosis, and apocrine metaplasia, were isolated from surrounding tissue by microdissection. LOH was observed at some frequency in each component analyzed, but was most often observed in this group of specimens in foci of apocrine metaplasia. Based on these findings, a group of breast carcinomas was studied for the presence of apocrine metaplasia foci adjacent to carcinoma. Genetic analysis of these foci provided evidence consistent with a developmental relationship between the apocrine metaplasia specimen and the adjacent tumor.
| Materials and Methods |
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The surgical pathology archives at the Louisiana State University Medical Center-Shreveport were searched for cases with a diagnosis of fibrocystic disease or fibrocystic change. Cases that contained carcinoma were excluded. Slides were reviewed to identify cases with dissectable foci of hyperplasia, adenosis, and apocrine metaplasia. A total of 32 cases were selected. Of these 32 cases, 24 were postmenopausal, two were premenopausal, and the menopausal status of the other six cases could not be ascertained. These cases are referred to with the designation FC followed by a case number to distinguish them from the breast cancer cases that were used in the second portion of the study presented in this report. The components of fibrocystic change were identified on hematoxylin and eosin-stained sections and then on unstained 12-µm sections after deparaffinization with Ameri-clear (Fisher). The individual foci were microdissected from surrounding tissue with a small scalpel blade. Because lymph nodes were not available for most of these cases, normal control specimens were taken from regions of the available sections rich in stromal or lymphoid cells. Tissue was placed in 75 µl of lysis buffer (120 µg/ml proteinase K, 50 mmol/L KCl, 10 mmol/L Tris (pH 8.0), 0.1 mmol/L EDTA, and 0.5% Tween 20) and incubated at 55°C for 1216 hours, followed by 95°C for 5 minutes to inactivate the protease. Insoluble debris was pelleted by centrifugation, and the supernatant was used as the source of DNA template for polymerase chain reaction (PCR).
Cases used for the identification of apocrine metaplasia adjacent to carcinoma were from the archives of the Armed Forces Institute of Pathology and have been described previously.16
PCR Conditions
The panel of markers used consisted of a group of 14 dinucleotide repeat polymorphisms known to have a high heterozygote frequency and to show a high frequency of LOH in breast cancer. The markers in the panel, and the associated tumor suppressor genes when known, included CI3-CA373 at chromosome 3p14,17 D9S171 and D9S1748 (p16 cdk inhibitor)18,19 at chromosome 9p; D11S4046 and TH (tyrosine hydroxylase) at 11p1516,20 ; D13S260 (BRCA2) and D13S263 (RB1) at 13q121421 ; D16S496, D16S512, and D16S421 at16q2222 ; D17S1788 and D17S1880 and P53 at chromosome 17p; and D17S795 at chromosome 17q.20
PCR reactions were performed in the presence of one 32P-end-labeled primer. PCR assays were performed in 20-µl reactions containing 10 mmol/L Tris-HCl (pH 8.3), 50 mmol/L KCl, 1.5 mmol/L MgCl2, 1 U of AmpliTaq Gold DNA Polymerase (Perkin-Elmer, Foster City, CA), 0.2 mmol/L of each deoxynucleoside triphosphate, 0.2 µmol/L primer, and 1 µl of the tissue lysate. A 5-minute 95°C denaturation step was followed by 40 cycles of 95°C for 30 seconds, 55-60°C for 30 seconds, 72°C for 30 seconds, and a 10 minute final extension step at 72°C. Reactions were stopped by the addition of loading buffer (95% formamide, 10 mmol/L EDTA, 0.1% bromophenol blue, and 0.1% xylene cyanol). The PCR products were heat denatured for 5 minutes at 95°C and loaded on a 6% acrylamide/7 mol/L urea gel. Results were visualized by autoradiography for 2 h to overnight at room temperature with Kodak XAR-5 film. In addition, to permit quantitation of allele ratios, gels were exposed to storage phosphor screens, and images were acquired with a Molecular Dynamics Storm Imaging System. Bands were quantitated by using the Molecular Dynamics ImageQuant software package.
Results were considered informative if the normal control specimen revealed a heterozygous genotype. A change in allele ratio of more than 50% relative to the normal control was interpreted as LOH.
| Results |
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Thirty-two cases showing fibrocystic change were selected for this
study. Components of fibrocystic change were isolated from these cases
by microdissection, resulting in a total of 90 specimens.
Microdissection permitted the isolation of highly purified populations
of the cells of interest, as illustrated in Figure 1
. The specimens included 27
morphologically normal TDLUs, 23 foci of adenosis, 19 of apocrine
metaplasia, and 21 of ductal hyperplasia. Each of these specimens was
analyzed for LOH at 14 dinucleotide repeat polymorphisms representing
seven chromosomal arms. These markers were chosen to represent loci
that show LOH with high frequency in breast cancer.23
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2
test for fit to a Poisson
distribution). Of the different morphological entities studied, LOH was
observed in 22% of normal TDLUs (6/27), 17% of adenosis (4/23), 19%
of hyperplasias (4/21), and 53% of apocrine metaplasia (10/19). The
difference in LOH frequency between apocrine metaplasia and the other
specimens was statistically significant (P =
0.002, Fisher exact test). In case 50, the microdissected hyperplasia
and apocrine metaplasia specimens shared LOH at five loci. This number
of shared genetic lesions provides strong support for a common
precursor cell in a lineage that developed into the two morphologically
distinct epithelial foci.
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| Discussion |
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We have presented allelotype findings in a group of normal and benign proliferative lesions isolated from surrounding tissue elements by microdissection. Polymorphic markers were chosen to represent loci known to show LOH with high frequency in malignant tumors of the breast.24,25 These loci represent chromosomal arms 3p, 9p, 11p, 13q, 16q, 17p, and 17q. Our results revealed that even in normal breast epithelium and in the absence of cancer, LOH at one or more loci in our panel can be detected in approximately 20% of specimens. In these specimens, LOH was detected with significantly higher frequency in apocrine metaplasia than in hyperplasia, adenosis, or normal breast epithelium. To our knowledge, the allelotype of apocrine metaplasia has not previously been reported.
The occurrence of LOH in benign breast epithelium presented an opportunity to analyze a panel of previously characterized breast carcinomas for the genetic relationship between apocrine metaplasia and an adjacent carcinoma. Apocrine metaplasia is easily recognized by its distinct morphology, distinguishing it from adenosis and hyperplasia, the cells of which may show morphological patterns and cellular changes that make differentiation from carcinoma difficult. In theory there were four possible kinds of relationship between the apocrine metaplasia and the carcinoma. First, they could be completely unrelated, deriving from lineages that diverged before the development of any of the abnormalities that lead to the malignant phenotype. Second, the carcinoma could be a direct descendent of the apocrine metaplasia. In this case, the apocrine metaplasia would be expected to show some but not all of the genetic changes detected in the carcinoma. Third, the two specimens might derive from developmental pathways that diverged after some but not all of the observed genetic alterations occurred. Finally, it is possible that the apocrine metaplasia developed from the carcinoma. LOH analysis does not permit definitive resolution of this issue, primarily because it is not possible to prove that LOH of the same allele in two different specimens results from one event rather than two independent events that coincidentally give the same result. Nevertheless, the finding of two cases that show identical LOH at three loci provides supportive evidence for the concept that a common precursor cell containing genetic abnormalities can develop into both apocrine metaplasia and carcinoma. The possibility that this might occasionally occur via direct progression from apocrine metaplasia to carcinoma is supported by the LOH results in cases 16 and 50.
The distribution of LOH events among the 90 specimens studied can be interpreted as evidence for a nonrandom occurrence of LOH. The data set generated from the fibrocystic change cases implies at least 61 independent LOH events, counting LOH at more than one marker on the same chromosomal arm as one event. These 61 events are not distributed equally among the 90 specimens, but are clustered together so that only 24 specimens demonstrated LOH at any of the markers. However, of the specimens that did show LOH, only five had LOH detected at only one marker. Thus there was a large excess of specimens with no LOH and with more than one locus showing LOH relative to what would be expected if the distribution of LOH events were random. We therefore interpret our results as suggesting that epithelial foci that show LOH have acquired a more general deficiency in the maintenance of chromosomal integrity. It appears that in the breast such a deficiency can arise not only during the development of the components of fibrocystic change, but even during the normal formation of the terminal duct lobular units.
The results of this study confirm the finding that LOH can occur in morphologically normal TDLUs and in components of fibrocystic change. The results further demonstrate that LOH occurs commonly in apocrine metaplasia and that LOH patterns in some cases suggest a common clonal precursor to apocrine metaplasia and an adjacent carcinoma. Finally, we observed an apparent clustering of genetic alterations in a nonrandom manner, suggesting that foci of cells emerge both during normal development and in fibrocystic changes that have acquired deficiencies in chromosomal maintenance, resulting in a high frequency of LOH.
| Footnotes |
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Supported by grant DAMD 17-94-J-4330 from the U.S. Army Medical Research and Materiel Command and by the intramural funds of the Armed Forces Institute of Pathology. C. W. and F. A. were supported by the Department of Pathology, Louisiana State University Medical Center, Shreveport. C. W. is currently supported by a fellowship from the Cancer Research Fund of the Damon Runyon-Walter Winchell Foundation.
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. This is a U.S. government work; there are no restrictions on its use.
Dr. Washingtons current address: Hamon Cancer Center, University of Texas Southwestern, 5323 Harry Hines Blvd., Dallas, TX 75235-8593.
Accepted for publication March 16, 2000.
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