A distinct molecular profile associated with mucinous epithelial ovarian cancer

Abstract

Mucinous epithelial ovarian cancers (MOC) are clinically and morphologically distinct from the other histological subtypes of ovarian cancer. To determine the genetic basis of MOC and to identify potential tumour markers, gene expression profiling of 49 primary ovarian cancers of different histological subtypes was performed using a customised oligonucleotide microarray containing >59 000 probesets. The results show that MOC express a genetic profile that both differs and overlaps with other subtypes of epithelial ovarian cancer. Concordant with its histological phenotype, MOC express genes characteristic of mucinous carcinomas of varying epithelial origin, including intestinal carcinomas. Differences in gene expression between MOC and other histological subtypes of ovarian cancer were confirmed by RT-PCR and/or immunohistochemistry. In particular, galectin 4 (LGALS4) was highly and specifically expressed in MOC, but expressed at lower levels in benign mucinous cysts and borderline (atypical proliferative) tumours, supporting a malignant progression model of MOC. Hence LGALS4 may have application as an early and differential diagnostic marker of MOC.

Figure 1

(A) Principal components analysis based on 500 genes with the most variable signal intensities (based on variance) separates the histological subtypes of EOC. MOC (n=3) are circled; (B) Hierarchical clustering and heat map of differentially expressed genes (n=167 upregulated and n=18 down-regulated) in MOC compared to serous and endometrioid ovarian cancers. Clustering was performed on all transcript profiled samples (n=3 MOC; n=4 mucinous borderline tumours; n=8 endometrioid ovarian cancers (endo); n=3 serous borderline tumours; n=31 serous ovarian cancers (unlabelled columns); and four normal ovaries) as described in the Materials and Methods. Expression levels are colour coded with red, green and black corresponding to an increase, a decrease, and no change in gene expression, respectively.

Figure 2

Semi-quantitative RT–PCR analysis of RNA expression in normal ovaries (n=2), mucinous borderline tumours (n=3), mucinous ovarian cancers (n=3) and serous ovarian cancers (n=3). RT-, no reverse transcriptase control; water, no cDNA. For gene descriptions, see Table 2 and Supplementary Data.

Figure 3

(A) mRNA transcript profile for LGALS4. The dashed line represents the signal intensity of the 15th percentile of the gene expression in normal body tissues (Henshall et al, 2003a); (B) representative immunohistochemistry staining for LGALS4 in MOC, serous ovarian cancer, normal ovarian surface epithelium (arrowed) and epithelial inclusion cysts (inset); × 40 magnification.

Figure 4

Box plots showing distribution of expression of LGALS4 in (A) normal ovarian surface epithelium (n=14) and in different histological subtypes of ovarian carcinoma: MOC (n=10); endometrioid ovarian cancer (n=22); serous ovarian cancer (n=55); clear cell ovarian cancer (n=8); and (B) in epithelial ovarian inclusion cysts (n=8); benign mucinous cysts (n=8); mucinous borderline tumours (n=29); low- (grade 1; n=6) and high-grade (grade 2–3; n=4) MOC; and low- (stage I; n=5) and high-stage MOC (stage II–III; n=5). For explanation of box plots, see Materials and Methods.