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The proposal that serous tubal intraepithelial carcinoma (STIC) is the precursor of ovarian high-grade serous carcinoma (HGSC) is based on several lines of investigation [1,2]. First, STICs are found in approximately 10–15% of Fallopian tubes removed prophylactically from women at high risk of developing ovarian carcinoma because of a germline BRCA mutation. Second, STICs are detected in 50–60% of cases of sporadic (without germline mutations of BRCA) ovarian, tubal,and so-called primary peritoneal HGSCs [3,4]. Third, STICs frequently up-regulate oncogene products, such as cyclin E1, Rsf-1, and fatty acid synthase, that are also overexpressed in HGSC [5]. Fourth, STICs have relatively shorter telomeres compared with concurrent ovarian HGSC, as occurs with precursor lesions in other sites. Finally, in a small series of five cases, STICs and concurrent ovarian HGSCs, the same TP53mutations were detected in STICs and HGSCs [12], indicating a potential clonal relationship. Besides exploiting the presence of TP53 mutations in STIC and HGSC as a method of showing a clonal relationship, detection of TP53 mutations in tissue specimens has utility in confirming the histological diagnosis of STIC since it has been reported that TP53 mutations occur in over 95% of ovarian HGSCs [6,7]. For histological diagnosis, however, detection of mutated TP53 is not practical and therefore immunohistochemical detection of p53 protein has been used as a surrogate marker. There have been only a few studies correlating p53 expression with TP53 mutation in ovarian HGSC [8–11] and none that we are aware of in STICs. Accordingly, we undertook the present study of STICs with concurrent pelvic HGSCs in order to (1) confirm a clonal relationship of STIC with HGSC in a relatively large series of cases, and (2) clarify the relationship of immunohistochemical expression of p53 protein with the mutational status of the TP53 gene.

Serous tubal intraepithelial carcinoma (STIC) has been proposed as a precursor for many pelvic high-grade serous carcinomas. Our previous analysis of the ovarian cancer genome identified several genes with oncogenic potential that are amplified and/or overexpressed in the majority of high-grade serous carcinomas. Determining whether these genes are upregulated in STICs is important in further elucidating the relationship of STICs to high-grade serous carcinomas and is fundamental in understanding the molecular pathogenesis of high-grade serous carcinomas. In this study, 37 morphologically defined STICs were obtained from 23 patients with stage IIIC/IV high-grade serous carcinomas. Both STICs and the high-grade serous carcinomas were analyzed for expression of Rsf-1 (HBXAP), cyclin E, fatty acid synthase (FASN) and mucin-4. In addition, they were examined for expression of established markers including p53, Ki-67 and p16. We found that diffuse nuclear p53 and p16 immunoreactivity was observed in 27 (75%) of 36 and 18 (55%) of 33 STICs, respectively, whereas an elevated Ki-67 labeling index (or=10%) was detected in 29 (78%) of 37 STICs. Cyclin E nuclear staining was seen in 24 (77%) of 35 STICs, whereas normal tubal epithelial cells were all negative. Increased Rsf-1 and FASN immunoreactivity occurred in 63%, and 62% of STICs, respectively, compared with adjacent normal-appearing tubal epithelium. Interestingly, only one STIC showed increased mucin-4 immunoreactivity. Carcinomas, when compared with STICs, overexpressed p16, Rsf-1, cyclin E and FASN in a higher proportion of cases. In conclusion, STICs express several markers including Rsf-1, cyclin E and FASN in high-grade serous carcinomas. In contrast, mucin-4 immunoreactivity either did not change or was reduced in most STICs. These results suggest that overexpression of Rsf-1, cyclin E and FASN occurs early in tumor progression.

There is compelling evidence to suggest that seroustubal intraepithelial carcinoma (STIC) is the likely primary sitefor the development of many pelvic high-grade serous carcino-mas (HGSCs). Identifying molecules that are upregulated inSTIC is important not only to provide biomarkers to assist inthe diagnosis of STIC but also to elucidate our understanding ofthe pathogenesis of HGSC. In this study, we performed RNAsequencing to compare transcriptomes between HGSC and nor-mal fallopian tube epithelium (FTE), and we identified LAMC1encoding laminin g1 as one of the preferentially upregulated genesassociated with HGSC. Reverse transcription polymerase chainreaction further validated LAMC1 upregulation in HGSC ascompared with normal FTE. Immunohistochemical analysis wasperformed on 32 cases of concurrent HGSC and STIC. The latterwas diagnosed on the basis of morphology, TP53 mutations, andp53 and Ki-67 immunohistochemical patterns. Laminin g1im-munostaining intensity was found to be significantly higher inSTIC and HGSC compared with adjacent FTE in all cases(P

There is mounting evidence that serous tubal intraepithelial carcinoma (STIC) is the immediate precursor of ovarian high-grade serous carcinoma (HGSC) (1–4) but the criteria for its diagnosis are not well established. A recent study, in fact, showed that interobserver reproducibility, even among expert gynecologic pathologists, was moderate at best (5). As more women with a family history of ovarian carcinoma undergo risk-reducing salpingo oophorectomy and as the SEE-FIM protocol, which allows more thorough evaluation of the fallopian tubes (6), becomes more widely used, this problem will become increasingly important. Pathologists will encounter not only STICs but other tubal abnormalities that may either be precursors of STICs or benign mimickers. In view of the difficulties in establishing a diagnosis on the basis of morphology alone, we have undertaken a number of studies to determine the most sensitive and specific methods of diagnosing STICs. We first investigated alterations in p53, because somatic mutation of TP53 is the most common molecular genetic change of HGSC. TP53 mutational status was correlated with p53 immunoreactivity and clinicopathologic characteristics (7). We found that STICs harbor TP53 mutations in the majority of the cases (91.3%) and these were the identical mutations found in the associated HGSC. Positive immunostaining for p53, however, depended on whether the mutations were missense mutations that resulted in strong staining or nonsense mutations that resulted in a truncated protein not recognized by the p53 antibody and therefore there was complete absence of staining. For these latter cases, in particular, we reasoned that the Ki-67 labeling index might be a useful adjunct to morphology and p53 immunostaining, because Mib1 staining would provide a sensitive and potentially quantifiable method of assessing proliferation in these lesions. Some previous studies have reported an increase in proliferation in STIC (range from 10% to 95%) compared with epithelium of the normal fallopian tube, but the range of the index in normal fallopian tube epithelium (FTE) has not been systematically evaluated so far (8,9). We therefore carried out the present study to determine the baseline Ki-67 proliferation index using Ki-67 staining in normal FTE compared with STICs.

Short telomeres are one of the main genetic manifestations in human cancer, as they have been shown to play an important role in inducing chromosomal instability and in contributing to tumor progression. The purpose of this study was to determine if changes in telomere length occur in serous tubal intraepithelial carcinoma (STIC), the putative precursor of "ovarian" high-grade serous carcinoma (HGSC). Twenty-two STICs from 15 patients with concurrent but discrete HGSCs were analyzed for telomere length on formalin-fixed, paraffin-embedded sections by conducting p53 immunofluorescence to assist in identifying STICs and telomere-specific FISH. Telomere length (short, long, or no change) in STICs was compared with HGSCs using normal fallopian tube epithelium and stromal cells as controls. We found that STICs had the shortest telomeres, as 18 (82%) of 22 STICs had short telomeres, whereas only 2 (9%) showed no change and 2 (9%) had long telomeres compared with the normal-looking tubal epithelium. In contrast, among 12 paired HGSCs and STICs, 6 HGSCs showed an increase in telomere length, one showed a decrease in length and 5 did not show any change when compared with their matched STICs, although, such as STICs, the majority of HGSCs had shorter telomeres than the associated normal tubal epithelial cells. These differences in telomere length between normal tubal epithelial cells and STICs, and between STICs and HGSCs were statisticaly significant (P