cytogenetics and molecular genetics of ovarian cancer

American Journal of Medical Genetics (Semin. Med. Genet.) 115:157–163 (2002)

A R T I C L E

Cytogenetics and Molecular Genetics ofOvarian CancerNANCY WANG*

Genetic alterations identified in human ovarian tumors by conventional banding, fluorescence in situ hybridization,comparative genomic hybridization, chromosome microdissection, loss of heterozygosity, chromosome microcell–mediated chromosome transfer, and microarray gene expression analysis are summarized and correlated. Thesignificance of these findings with respect to pathologic classification and clinical application are discussed.� 2002 Wiley-Liss, Inc.

KEY WORDS: genetic changes; ovarian cancer; fluorescence in situ hybridization; comparative genomic hybridization; chromosomemicrodissection; chromosome transfer; microarray gene expression analysis

INTRODUCTION

With a 5-year survival rate of 20–30%,

ovarian cancer is the leading cause of

death from gynecological malignancies

and the fifth most common cause of

cancer death among women [Gajewski

and Legare, 1998]. Most ovarian cancers

are asymptomatic and, therefore, usually

are not diagnosed until an advanced

stage. Many genetic changes are involv-

ed in the development of both sporadic

and hereditary cases of ovarian cancer.

The genetic changes basically are relat-

ed to the activation/overexpression of

oncogene(s) and inactivation/underex-

pression of tumor suppressor gene(s).

Identifying the carcinogenesis-related

genetic defects could facilitate or im-

prove the basic understanding, early

detection, diagnosis, prognosis, and

therapeutic monitoring of ovarian can-

cer. The approaches used for the identi-

fication of sequential genetic alterations

associated with ovarian cancer develop-

ment, similar to those applied to other

forms of neoplasia, first focused on

chromosomes. These methods include

conventional banding, fluorescence in

situ hybridization (FISH), chromosome

microdissection, and comparative geno-

mic hybridization (CGH) analyses.

Most ovarian cancers are

asymptomatic and, therefore,

usually are not diagnosed until

an advanced stage.

Oncethechromosomal‘‘hotspot(s)’’

are pinpointed, molecular approaches,

such as array CGH and loss of hetero-

zygosity (LOH) analysis with microsa-

tellite markers mapped to the hot spot

regions, can be applied to narrow the

target from the chromosome to the

gene-locus level. In addition to geno-

mic analysis, candidate tumor suppressor

gene(s) can be verified functionally by

microcell-mediated chromosome trans-

fer or gene transfection study or both. In

recent years, the availability of cDNA

microarray and quantitative real-time

reverse transcription–polymerase chain

reaction (RT-PCR) has made it possible

to identify the genetic changes at the

level of the gene expression profile. The

application of these approaches in the

identification of some genetic alterations

associated with the predisposition, gen-

esis, progression, metastasis, and survival

rate of human ovarian cancer are sum-

marized and discussed in this article.

CHROMOSOMALABERRATIONS DETECTEDBY CONVENTIONALBANDING ANALYSISAND FISH

As reviewed by Hauptmann and Dietel

[2001], 37% of serous tumors of low

malignant potential have chromosomal

aberrations; trisomies of 7, 8, and 12

frequently are identified. In contrast,

91% of invasive serous carcinomas of

low-grade malignancy have been found

to have clonal chromosomal aberra-

tions. Tibiletti et al. [2001] analyzed

15 ovarian-surface epithelial tumors of

borderline malignancy by G-banding,

LOH, and FISH. Deletion of 6q27

between D6S149 and D6S193 was

the smallest deletion detected. Because

del(6)(q27) also was found in both

advanced and benign ovarian tumors,

Tibiletti et al. [2001] proposed that

gene(s) located at 6q27 may play a crucial

role in the early events of ovarian tumor

development and that there is a con-

tinuum in the progression model of

ovarian neoplasia. Using interphase

FISH analysis, Diebold et al. [2000]

Dr. Nancy Wang is the Director of theCytogenetics Laboratory and Professor ofPathology, Genetics, and Pediatrics at theUniversity of Rochester School of Medicine,Rochester, New York. Her main researchinterest is the study of human ovarian cancerusing various cytogenetic, molecular cytoge-netic, and molecular genetic approaches.

*Correspondence to: Nancy Wang, Ph.D.,Department of Pathology and LaboratoryMedicine, 601 Elmwood Avenue—Box 608,Rochester, New York 14642.E-mail: [email protected]

DOI 10.1002/ajmg.10695

� 2002 Wiley-Liss, Inc.

detected a high frequency of gain of

20q13.2 (70%) and cyclin D1 (72%) and

suggested its association with adverse

prognosis.

Tibiletti et al. . . . proposed

that gene(s) located at 6q27 may

play a crucial role in the

early events of ovarian tumor

development and that

there is a continuum in the

progression model of

ovarian neoplasia.

Taetle et al. [1999b] analyzed the

chromosome composition of 244 pri-

mary ovarian adenocarcinomas. Clonal

chromosomal aberrations were detected

in 201 tumors. Structural abnormalities

were identified in 134 of the tumors,

with the nonrandom breakpoints clus-

tered at chromosomes 1 (p1, q1, p2, q2,

p3, q3, and q4), 3 (p1), 6 (q1, p2, and q2),

7 (p1, q1, and p2), 11 (p1, q1, and q2), 12

(p1 and q2), 13 (p1), and 19 (q1).

Homogeneously staining regions (hsr)

were identified in 20 cases (16.4%), with

more than 1 hsr identified in five cases.

The prognostic impact of these nonran-

dom aberrations was investigated by

Taetle et al. [1999a] using log-rank and

proportional hazards regression analysis.

They found that the aggregate presence

of a chromosome breakpoint in anyof 21

nonrandomly involved regions and

breaks in nine distinct regions (1p1,

1q2, 1p3, 3p1, 6p2, 11p1, 11q1, 12q2,

and 13p1) were associated with reduced

patient survival rate and time. Further-

more, using the approach of propor-

tional hazards regression, it was found

that only breakpoints within 1p1 and

3p1 retained independent, deleterious

effects on survival and clinical variables

associated with survival. Simon et al.

[2000] further applied seven techniques

from statistics, theoretical computer,

science, and phylogenetics to analyze

the cytogenetics data obtained from

these 244 cases.

All methods led to strikingly con-

sistent conclusions about chromosome

breakpoints in human ovarian adeno-

carcinoma. The conclusions were that

(1) nonrandom breakpoints in ovarian

adenocarcinoma do not occur indepen-

dently, (2) breakpoints in regions 1p3

and 11p1 are important early events

and mark a class of tumors with poor

prognosis, and (3) breakpoints in 1p1,

3p1, and 1q2 distinguish a class of ova-

rian tumors and, furthermore, the breaks

at 1p1 and 3p1 are associated with poor

prognosis. Bello and Rey [1990] have

reported aberrations of chromosomes

1 and 3 as the ones most frequently found

in ovarian metastic tumors. These large-

scale-series studies on chromosomal

structural aberrations in ovarian tumors

have confirmed the nonrandom break-

points identified previously by other

investigators [Bello and Rey, 1990; Gal-

lion et al., 1990; Roberts and Tattersall,

1990; Pejovic et al., 1992; Jenkins et al.,

1993; Kiechle-Schwarz et al., 1994;

Thompson et al., 1994; Pejovic 1995;

Iwabuchi et al., 1995; Deger et al., 1997].

In addition to structural aberrations,

these conventional karyotypic studies also

found nonrandom gains of chromosomes

1,2,3,6,7,9,and12andlossesof X,4,11,

13, 15, 17, and 22.

GENETIC IMBALANCEDETECTED BY CGH

Kallionemi et al. [1992] showed that

genome-wide detection of unbalanced

genetic changes on metaphase chromo-

somal regions can be achieved by CGH.

With the exception of highly amplified

genes, the resolution of CGH is approxi-

mately 3–5 Mb [Kallionemi et al.,

1994]. A comparative analysis between

CGH and conventional banding analysis

found that CGH can detect a wide range

of quantitative alterations involving a

single chromosome band as well as gene-

tic alterations that are not detectable by

other approaches [Nacheva et al., 1998].

Jacobsen et al. [2000] applied both CGH

and interphase FISH analysis with dif-

ferent probes to 10 ovarian carcinomas.

The CGH results in 66.2% (92 of 139

loci) of the cases were confirmed by

FISH. The inconsistent results in the

remaining cases were due to either poly-

ploid, which cannot be detected by

CGH, or the limitations of both ap-

proaches. This study provides evidence

of the reliability of CGH.

Suzuki et al. [2000] performed a

large-scale correlation study between

the CGH-detected genome changes

and clinical end points in 60 ovarian

cancer cases. They found an association

between the loss of chromosome 4 and

high-grade tumors and between gains of

3q26-qter, 8q24-qter, and 20q13-qter

and low-grade and low-stage tumors.

Furthermore, deletion of 16q24 and

more than seven independent genome-

copy-number aberrations were associat-

ed with reduced survival times. Most

important, tumor grade was found to

correlate better with the extent of geno-

mic progression than with clinical stage.

Kiechle et al. [2001] analyzed 106 pri-

mary ovarian carcinomas by CGH, 103

carcinomas showed genetic imbalance,

with the regions 8q, 1q, 20q, 3q, and 19p

amplified in 69–53% of tumors and

the regions13q, 4q, and 18q under-

represented in 54–50% of the tumors.

Furthermore, underrepresentation of

11p and 13q and overrepresentation of

8q and 7q were found to correlate with

undifferentiated ovarian carcinoma. In

contrast, 12p underrepresentation and

18p overrepresentation were found more

frequently in well-differentiated and

moderately differentiated tumors. The

significant aberrations were translated

into a score system, which can be used

easily for the prediction of an undiffer-

ented phenotype; the system has a spe-

cificity of 79% and a sensitivity 86%.

Watanabe et al. [2001] performed

CGH analysis on 17 ovarian carcinoma

cell lines. Again, the most frequent gains

were found at 20q12-13 (47.1%), 8q23-

24 (35.2%), 5p15 (23.5%), 7q32-36

(23.5%), and 20p (23.5%), whereas the

most frequent losses were found at

18q22-23, 13q22-23, 9p, 4p11-14, and

11p14-15. High-level amplifications

were detected at 20q12-13, 8q24,

12p11-12, and 17q21-23. High-level

amplification of 3q26, 8q24, and 20q13

also has been detected by Sonoda et al.

[1997]. Arnold et al. [1996] also found

gains of 3q and 8q and losses of 18q.

Genetic imbalance patterns have

been compared in sporadic and heredi-

158 AMERICAN JOURNAL OF MEDICAL GENETICS (SEMIN. MED. GENET.) ARTICLE

tary ovarian cancers. Patael-Karasik et al.

[2000] applied CGH analysis to 12 in-

vasive epithelial tumors (including three

BRCA1 and one BRCA2 mutation

carriers), two primary peritoneal carci-

nomas, one pseudomyxoma peritonei

tumor, and one Serotoli cell tumor.

The most common abnormalities in

epithelial tumors were amplification

of 8q22.1-ter (66.6%), 1q22–32.1

(41.1%), 3q (75%), and 10p (33.3%)

and deletion of 9q (41.6%) and 16q21–

24 (33.3%). A chromosome 9q deletion

was found in all three BRACA1 carriers

and two of eight sporadic cases, whereas

a deletion od chromosome 19 was seen

in two of three BRCA1 mutation

carriers but none of the sporadic cases.

The result indicates that there are

preferential somatic mutations of chro-

mosomes 9 and 19 in BRCA1 mutation

carriers. Tapper et al. [1998] identified

extensive similarity in genetic imbalance

between sporadic and inherited ovarian

carcinomas, with the exception of

chromosome 2q24-q32.

Zweemer et al. [2001] applied

CGH to 36 microdissected hereditary

ovarian cancers. Theyobserved frequent

gain at regions 8q23-qter, 3q26.3-qter,

11q22, and 2q31-32 and frequent

losses at regions 8p21-pter, 16q22-qter,

22q13, 12q24, 15q11-15, 17p12-13,

Xp21-22, 20q13, 15q24-25, and 18q21.

The majority of these genetic imbal-

ances are similar to those found in

sporadic cases of ovarian cancer. Dele-

tions of 15q11-15, 15q24-25, 8p21-ter,

22q13, and 12q24 and gains at 11q22,

13q22, and 17q23-25, however, appear

to be specific to hereditary ovarian can-

cer. Of 36 cases, deletions of 15q11-15

and 15q24-25 were found in 16 and 12

cases, respectively, which indicates the

possible involvement of hRAD51 and

other important tumor suppressorgene(s)

located at these regions in the carcino-

genesis of familiar ovarian cancer.

GENE AMPLIFICATIONIDENTIFIED BY CGH, FISH,AND CHROMOSOMEMICRODISSECTION

As mentioned in the previous section,

CGH studies have detected a high level

of amplifications at the chromosomal

regions 8q, 1q, 20q, 3q, and 19p. Tanner

et al. [2000] studied the amplification

of the chromosome region 20q in 24

sporadic, three familial, and four heredi-

tary ovarian carcinomas and eight ovar-

ian cancer cell lines by CGH and

FISH with probes specific for the

genes E2F, AIB3/AIB4, SRC, AIB1,

MYB2, PTPN1/PTP13, RMC20P400,

ZNF217 and BTAK/STK15/Aurora 2.

High-level amplification of at least one

of the five separate regions at 20q12-

q13.2 was found in 54% of sporadic cases

and all forms of hereditary tumors. The

regions defined by AIB1 (20q12) and

PTPN1 (20q13.1) genes were amplified

in 25% and 29% of the sporadic tumors,

respectively. Furthermore, the amplifi-

cation of AIB1, a steroid receptor co-

activator gene [Anzick et al., 1997],

was found to correlate with a positive

estrogen receptor and poor survival of

patients.

The high frequency of gene ampli-

fication at 20q12-q13.2 indicates that

overpresentation of these genes may play

a crucial role in the pathogenesis of

ovarian cancer [Tanner et al., 2000].

Imoto et al. [2000] cloned and se-

quenced a novel homeobox gene,

TGIF2, located at 20q11.2-12, which

was found to be amplified and over-

expressed in 14 ovarian cancer cell lines.

TheERBB2oncogene, located at 17q21,

was found to be amplified and over-

expressed in 9–30% of ovarian cancers

[Levan et al., 1977; Kovaks, 1979;

Fukushi et al., 2001]. The overexpres-

sion of ERBB2 has been found to be

correlated with poor survival of patients

[Kovaks, 1979]. Amplification of the

MYC oncogene, which is located at

8q24, has been noted in 10–20% of

ovarian cancers, more frequently in

serous than in mucinous types [Kovaks,

1979]. The oncogenes KRAS, INT2,

FMS, MDM2, and AKT2 were ampli-

fied in 3–5% of ovarian cancers [Kovaks,

1979]. Overexpression of p53, EDFR,

cerB2, and c-erB3 has been found in

endometriod carcinoma of the ovary

[Leng et al., 1997].

The Kallikrein gene 4 (KLK4),

located at 19q13.4, can be upregulatd

by androgen in prostate cancer cell lines

and by androgen and progestins in

breast cancer cell lines. Using RT-

PCR, Obiezu et al. [2001] detected the

expression of KLK4 in 69 of 147 (55%)

ovarian cancer samples and found a

strong positive association between

higher KLK4 expression and poor

prognosis. Guan et al. [2001] isolated a

novel candidate oncogene within a

frequently amplified region at 3q26 in

ovarian cancer. The hsr, a cytogenetic

indication of gene amplifications, has

been found in about 20% of ovarian

tumors [Taetle et al., 1999]. Using

chromosome microdissection combin-

ed with FISH, Guan et al. [1995]

found DNA sequence amplification at

19q13.1-q13.2, which is the candidate

site for AKT2, a serine threonine kinase

gene, in three of seven ovarian cancers.

Amplification of the C-MYC gene

has been detected in ovarian cancer

by Southern hybridization and PCR

[Baker et al., 1990; Sasno et al., 1990;

Schreiber and Dubeau, 1990; Bau-

knecht et al., 1993]. Our laboratory

[Abeysinghe et al., 1999] employed the

micro-FISH approach to show that the

amplification of C-MYC is the origin

of an hsr in two ovarian carcinoma cell

lines.

DETECTION OF TUMORSUPPRESSOR GENEBEARING REGIONS BYLOH ANALYSIS

The CGH approach identified nonran-

dom deletions of chromosome regions

Xp21-22, 1p31, 4p11-14, 8p21-pter,

9p, 11p14-15, 12q24, 13q22-23, 15q11-

15, 15q24-25, 16q22-qter, 17p12-13,

20q13, 18q22-23, and 22q13. LOH ana-

lysis on microsatellite markers mapped

The high frequency of gene

amplification at 20q12-q13.2

indicates that overpresentation

of these genes may play a crucial

role in the pathogenesis of

ovarian cancer.

ARTICLE AMERICAN JOURNAL OF MEDICAL GENETICS (SEMIN. MED. GENET.) 159

to these ‘‘target’’ regions can localize the

potential tumor suppressor from the

chromosome to the gene-locus level.

Weitzel et al. [1994] did LOH analysis on

27 primary epithelial ovarian tumors

using 19 polymorphic markers on chro-

mosomes 1, 5, 6, 9, 11, 13, and 17. They

found LOH at 5q21 (APC), 9p (IFNA),

11p15, 11q13, 11q24, 17q22, q24, and

11p11, with a frequency of 50%, 53%,

50%, 25%, 29%, 50%, 39%, and 64%,

respectively. Launonen et al. [2000]

applied LOH analysis to PCR-amplified

DNA from 78 paraffin-embedded

tumor and normal tissue pairs. In 17

cases, the metastic tumors were analyzed

in addition to the primary tumors. A

69% LOH was observed at 17p13.1,

where the TP53 gene is located.

The frequency of LOH at 3p14.2,

11p15.5, 11q23.3, 11q24, 16q24.3, and

17p13.1 in advanced-stage tumors is

significantly higher than in lower-stage

tumors. LOH at 3p14.2 was found to

be associated with tumor metastasis,

whereas LOH at 11p15.5 and 11q23.3

was found to be associated with reduced

cancer-specific survival time. Launonen

et al. [1998] performed LOH analysis on

49 epithelial ovarian cancers for the

region 11q22.3-q25. LOH was detected

in 61% of cases. LOH for markers at

11q23.3 is associated with significantly

reduced survival time and serous tumor

histologic characteristics, whereas LOH

at 11q24-q25 correlates with a higher

tumor stage, serous tumor histologic

features, and presence of residual tumor

but not with survival times. Watson et al.

[1998] performed an LOH study on 40

early-stage malignant and seven border-

line ovarian tumors. LOH of 7p (31%),

7q (50%), 9p (42%), and 11q (34%) was

identified in the early-stage tumors.

Borderline tumors have an LOH pattern

similar to that of early-stage malignant

tumors, indicating that malignant ovar-

ian tumors may arise from benign and

borderline tumors.

Kurose et al. [2001] applied LOH

analysis to 68 ovarian cancers, which

showed a 45% LOH at 10q23.3, flanking

PTEN and withinPTGN.Furthermore,

the loss of PTEN expression was found

to be linked to elevated phosphorylated

Akt levels but was not associated with

p27 and cyclin D1 expression in primary

epithelial ovarian carcinomas. Allelic

deletion at 1p31 has been detected in

approximately 40% of ovarian cancers

by Yu et al. [1999]. Using differential

display PCR, a maternally imprinted

tumor suppressor gene,NOEY2 (ARHI),

for both breast and ovarian cancers was

mapped to the 1p31 region. Alvarez et al.

[2001] applied LOH analysis on paired

normal/tumor DNA samples from 21

early-stage (I and II) and 54 advanced-

stage (III and IV) ovarian cancers to

detect the allelic loss at chromosome

1p36. An LOH frequency of 73% was

found in poorly differentiated ovarian

cancer, whereas a 48% (P¼ 0.03) LOH

was found in moderately differentiated

cases, suggesting that LOH on 1p36 is

associated with poor histologic grade.

Wang et al. [2001] performed LOH

analysis for chromosomes 5 and 6 on

29 primary early-stage epithelial ova-

rian carcinomas. A high frequency of

deletion was identified in regions

5p15.2, 5q13-21, 6p24-25, 6q21-23,

and 6q25.1-27, suggesting the presence

of tumor suppressor genes in these

regions. The region 7q31.1, a known

fragilesite, is frequentlydeletedinavariety

of human neoplasms, including ovarian

cancer.A transformationsuppressorgene,

caveolin 1, has been identified at this

region by Engelman et al. [1998].

Lassus et al. [2001] performed

comparative LOH analysis comparing

serous and mucinous ovarian carcinomas

on the region 8p21-p23. LOH of 67%

and 21% in three distinct regions,

8p21.1, 8p22-p23.1, and 8p23.1, was

detected in serous and mucinous carci-

nomas, respectively. Furthermore, in

serous carcinoma, LOH was associated

with higher-grade tumors. The expres-

sion of a transcription factor gene,

GATA4, located at 8p23.1 was found

to be lost in most serous carcinomas but

retained in the majority of mucinous

carcinomas, suggesting distinct patho-

genetic pathways in serous and muci-

nous ovarian carcinomas. Pribill et al.

[2001] performed LOH analysis on 70

ovarian tumors at the regions 8p12-p21

and 8p22-pter. Allelic imbalance was

found in 54 tumors (77%). Poorly

differentiated and advanced-stage can-

cers had a 66% and 54% LOH, respec-

tively. In contrast, well-differentiated

and early-stage tumors had an LOH of

20% and 36%, respectively. The smallest

regions of overlap were at 8p12-p21 and

8p23, suggesting the existence of genes

related to the progression of epithelial

ovarian cancer in these regions.

Faulkner and Friedlander [2000]

performed LOH analysis on 35 cases of

malignant ovarian germ cell tumors for

the chromosomal regions 3q, 5q, 9p, 11p,

11q, 12q, 17p, and 18q, which are

commonly involved in testicular germ

cell tumors. A high frequency of deletion

was detected at 3q27-q28 (50%), 5q31

(33%), 5q34-q35 (46%), 9p22-p21

(32%), and 12q22 (53%), which fre-

quently are deleted in testicular germ

cell tumors, suggesting that these chro-

mosomal regions may contain tumor

suppressor genes related to the carcino-

genesis of both ovarian and testicular

germ cell tumors.

Approximately 5–10% of ovarian

cancercaseshaveahereditarybasis [Narod

et al., 1994]. The first-degree relatives of

an ovarian cancer patient are expected to

havea twofold to fourfold increasedriskof

this cancer [Goldgar et al., 1994].

There are two distinct groups of

familial ovarian cancers: site-specific

ovarian cancers and breast-ovarian can-

cers. Germ-line mutations of BRCA1

are responsible for about 45% of familial

breast cancers and 80% of familial breast-

ovarian cancers. BRCA2 carriers have a

higher risk of early-onset breast cancer,

and these cases may account for 10–35%

of familial ovarian cancers. It is suggested

that BRCA1 and BRCA2 are involved

in two fundamental cellular functions:

DNA-damage repair and transcription

regulation [Welcsh and King, 2001].

About half of familial ovarian cancers

are not associated with BRCA1 or

BRCA2mutations. A susceptibility gene

for familial ovarian cancer has been

Approximately 5–10%

of ovarian cancer cases have a

hereditary basis


localized to chromosome 3p22-p25 by

genome-wide linkage analysis and LOH

analysis. The frequency of LOH of four

markers in the 3p22-p25 region is much

higher (52%) in non-BRCA1/BRCA2

familial ovarian cancers than in the

BRCA1 (29.7%) group [Sekine et al.,

2001].

BRCA2 carriers have a

higher risk of early-onset breast

cancer, and these cases may

account for 10–35% of familial

ovarian cancers.

FUNCTIONAL DETECTIONOF A TUMORSUPPRESSOR GENE BYMICROCELL-MEDIATEDCHROMOSOME TRANSFERAND TRANSFECTION

The chromosomal regions frequently

involved in LOH by microsatellite poly-

morphism analysis, in deletion by CGH,

and in structural aberrations by banding

analysis are candidate tumor suppressor

gene–bearing regions. The presence of

a functional tumor suppressor gene(s) on

a chromosome for a particular tumor can

be verified functionally by microcell-

mediated chromosome transfer [Trent

et al., 1990; Rimessi et al., 1994]. It has

been shown that the transfer of chromo-

some 3 suppresses tumorigenicity in

the ovarian carcinoma cell line HEY

[Rimessi et al., 1994] and that the

transfer of chromosome 6, especially

the region 6q24-25, induces senescence

in ovarian carcinoma cell lines SKOV-3

and OVCAR3 [Sandhu et al., 1996;

Wan et al., 1999]. Deletions at 6q27

were detected in 18 of 20 benign ovarian

tumors [Tibiletti et al., 1998]. Acquati

et al. [2001] cloned and characterized

gene RNASE6PL, located at 6q27. The

expression of this gene was found to

be reduced in 30% of primary ovarian

tumors and in 75% of ovarian cell lines.

Transfection ofRNASE6PL cDNA

into ovarian cancer cell lines HEY4 and

SG10G leads to suppression of tumor-

igenicity. The RNASE6PL gene there-

fore is considered to be a candidate

senescence-inducing and class II tumor

suppressor gene in ovarian cancer. Simi-

larly, transfer of chromosome 22 into

the ovarian carcinoma cell line SKOV-

3 leads to a complete abrogation of

anchorage-independent cell growth and

a dramatic reduction of in vitro doubling

times and tumorigenicity in nude mice.

Additionally, it is evident by microsatel-

lite marker polymorphism analysis that

a tumor growth suppressor gene is

located between markers D22S301 and

D22S304 in the region of 22q11-q12

[Kruzelock et al., 2000]. The functio-

nal roles of chromosomes 11 and 17 in

the carcinogenesis of ovarian carcinoma

have not been thoroughly investigated,

though chromosomes 11 and 17 have

been implicated in many types of human

neoplasia. Several studies have found

nonrandom LOH in human ovarian

carcinoma cells at the following chro-

mosomal regions: 11p15.5, 11p13,

11q22, 11q23.3-qter, 17p13.3, and

17p11.2. The LOH data suggest that

chromosomes 11 and 17 may carry a

tumor suppressor gene or genes for

ovarian carcinoma.

To test this hypothesis, Cao et al.

[2001] from our laboratory applied

microcell-mediated chromosome trans-

fer to introduce a normal chromosome

11 or 17 into the tumorigenic ovarian

carcinoma cell line SKOV-3. Complete

suppression of tumorigenicity was ob-

tained by the transfer of chromosome 11,

whereas a prolonged latency period and

reduction of in vitro and in vivo growth

rates were noted with the transfer

of chromosome 17. Furthermore, the

transfer of the region 17p11.2 by itself

had the same effect as the transfer of

the whole chromosome 17. The results

indicated the presence of a tumor sup-

pressor gene or genes on chromosome

11 and a tumor growth–inhibitor gene

or genes on chromosome 17, very likely

at the region 17p11.2.

GENE EXPRESSIONPROFILE ANALYSIS

The recently established cDNA micro-

array approach allows for the simulta-

neous analysis of the expression profiles

of thousands of genes [Schena et al.,

1995; Duggan et al., 1999]. Using this

cDNA microarray technology, Ismail

et al. [2000] identified a group of 60

genes differentially expressed between

10 ovarian tumors and five epithelial

cell lines. Some of these genes encode

membrane-associated or secreted pro-

teins, which potentially can be applied

to the development of serum-based

diagnostic markers for ovarian cancer.

Using the same approach, Ono et al.

[2000] identified differentially expres-

sed genes associated with ovarian carci-

nogenesis and the molecular separation

between serous and mucinous adeno-

carcinomas. Furthermore, differences

in gene expression were identified

between serous adenocarcinoma and

benign serous adenoma as well as be-

tween advanced and/or moderately or

poorly differentiated and local, highly

differentiated serous adenocarcinomas

[Tapper et al., 2001].

cDNA microarray analysis is a very

sensitive method. The development of

an efficient tyramide signal-amplifica-

tion system in the microarray system

enables analysis of gene expression with

20–100 times less total RNA, greatly

facilitating gene expression profile

study [Wong et al., 2001]. Nonetheless,

cDNA array cannot provide quantitative

analysis of gene expression on a large

number of specimens. In contrast, quan-

titative real-time RT-PCR [Heid et al.,

1996], a highly sensitive and reprodu-

cible technique, allows for the analysis

of specific gene expressions on a large

number of specimens. Using real-time

RT-PCR, Hough et al. [2001] identified

several genes coordinately upregulated

in ovarian cancer, suggesting the exis-

tence of common signaling pathways

in ovarian carcinogenesis. This infor-

mation has significant potential in the

identification of tumor-specific markers

as well as in the development of thera-

peutic strategies for ovarian cancers.

In summary, studies using cyto-

genetic, molecular cytogenetic, and

molecular genetic approaches obtained

correlated results on the genetic changes

associated with the carcinogenesis and

progression of human ovarian cancer.


This information potentially can be

applied in the early detection, diagnosis,

prognosis, and therapeutic treatment of

the disease.

ACKNOWLEDGMENTS

I express my appreciation to Dr. Jia Xu

and Mr. Ohn Chow for assistance in the

literature search, to Ms. Connie Yahn

for typing, and to Mr. Ohn Chow for

manuscript editing.

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cytogenetics and molecular genetics of ovarian cancer

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