The remaining 53 tumors subsequently had p53 immunostaining done; all 49 LGEC showed wild-type staining and the serous carcinoma and 1/2 HGEC showed mutant pattern staining.
In contrast, the SC component showed a mutator-phenotype and prominent genome instability along with biallelic inactivation of TP53, but none of them were found in organoids or the CCC component.
Using an illustrative case study and a review of the literature, we explore a relatively routine diagnostic question: whether the negative predictive value of a wild-type p53 immunophenotype for serous carcinoma is absolute, that is, whether a p53-wild type immunophenotype is absolutely incompatible with a diagnosis of serous carcinoma.
Based on aberrant staining for p53 and p16, 17/43 (40%) of the high-grade endometrial carcinoma cases initially diagnosed as high-grade endometrioid carcinoma were re-classified as serous carcinoma.
Pure SC almost always resided in the p53 abn group (positive predictive value: 96%), but it was insensitive as a marker of p53 abn (sensitivity 64%) and the reproducibility of diagnosing SC was suboptimal.
The overall mutation profile of this cohort of endometrial CCC appears to be more serous-like than endometrioid-like, with a minor subset in the TP53-mutated CCC showing serous carcinoma profile.
None of the tumors demonstrated nuclear beta-catenin expression. p53 mutations appear to be a powerful molecular marker for ovarian high-grade serous adenocarcinoma.
In this model, endometrial serous carcinoma arises predominantly in the resting endometrium, manifesting first as p53 immunoreactive, morphologically normal endometrial cells (p53 signatures), evolving to endometrial glandular dysplasia (which is the first morphologically identifiable precursor lesion), then to serous endometrial intraepithelial carcinoma (a carcinoma with a noninvasive growth pattern in the uterus but which is not infrequently associated with extrauterine disease), and finally into fully developed serous carcinoma.
From this first comprehensive mapping of TP53 mutation rate in a homogeneous group of HGPSC patients, we conclude that mutant TP53 is a driver mutation in the pathogenesis of HGPSC cancers.
In their paper in this issue of the Journal, Xian et al have analysed in detail the Fallopian tubes from two patients with Li-Fraumeni syndrome (germline TP53 mutation) in order to investigate further the possible role of p53 signatures in the development of high-grade pelvic serous carcinoma.
The present study examines a serous carcinoma with choriocarcinomatous differentiation. p53 staining was seen in the serous component and the cytotrophoblastic cells of the choriocarcinomatous component, but not in the syncytiotrophoblastic cells. p53 mutational analysis showed a heterozygotic mutation at exon 8 for the choriocarcinomatous component and a homozygote deletion at exon 7 for the serous component.
Current data indicate that each of these histologic subtypes is associated with distinct morphologic and molecular genetic alterations: high-grade serous and possibly endometrioid carcinomas most probably arise from surface epithelial inclusion glands with TP53 mutations and dysfunction of BRCA1 and/or BRCA2; low-grade serous carcinomas probably arise in a stepwise fashion in an adenoma-borderline tumor-carcinoma sequence from typical to micropapillary borderline tumors to low-grade invasive serous carcinoma via activation of the RAS-RAF signaling pathway secondary to mutations in KRAS and BRAF; mucinous carcinomas arise via an adenoma-borderline tumor-carcinoma sequence with mutations in KRAS; low-grade endometrioid carcinomas arise from endometriosis via mutations in CTNNB1 (the gene encoding beta-catenin) and PTEN.
In serous carcinoma, p53 mutation is the most frequent genetic alteration, followed by inactivation of p16 and e-cadherin and amplification of her2/neu. p53 mutation occurs in endometrial intraepithelial carcinoma, the putative precursor of serous carcinoma.
The incidences of p53 mutation and p53 nuclear immunoreactivity also differed between CCA and SEA: 0% and 7% in the former and 64% and 45% in the latter (P = 0.0006 and 0.039).
Although this study included a relatively small number of cases and therefore is a preliminary study, these results suggest that the dominant-negative mutation of the TP53 gene is related to serous adenocarcinoma.
Whereas endometrioid carcinoma and endometrial hyperplasia are associated with microsatellite instability and ras and PTEN mutations, serous carcinoma and endometrial intraepithelial carcinoma are associated with p53 mutations and abnormal accumulation of p53 protein.
LOH of the ESR marker was detected in 4 (50%) of 8 informative SCa, but in 0 of 4 informative CCa and 1 (16%) of 6 informative SLMP. p53 protein overexpression was present in 8 of 12 SCa but did not correlate to TP53 LOH.
The presence of p53 gene mutations in EIC further suggests that p53 alteration plays an important role early in the pathogenesis of serous carcinoma, possibly accounting for its aggressive biological behavior.
As high-grade ovarian tubal serous carcinoma is known to be associated with BRCA1/2 pathogenic germline mutations (PMs), we aimed to explore whether USC is also a constituent of hereditary breast and ovarian cancer syndrome.