High-grade serous carcinoma arising in a low-grade serous carcinoma and micropapillary serous borderline tumour of the ovary in a 23-year-old woman

Early genetic divergence of high-grade carcinomas originating from low-grade ovarian serous neoplasms

The current paradigm implicates a fallopian tube precursor as the origin of most ovarian high-grade serous carcinomas (HGSC). However, a rare subset of HGSCs develop via a distinct pathway from low-grade serous ovarian neoplasms (namely, serous borderline tumor and low-grade serous carcinoma). This alternate pathway for the development of HGSC and other poorly differentiated carcinomas of the ovary is not well understood. To elucidate the molecular pathogenesis and evolutionary trajectory of histologic transformation of low-grade serous neoplasms, we performed whole exome sequencing on microdissected low-grade and higher-grade components from 7 cases of serous borderline tumor or low-grade serous carcinoma associated with a synchronous or metachronous indeterminate/high-grade carcinoma. In most cases, there were relatively few somatic mutations shared between matched low-grade and higher-grade tumors compared to private mutations specific to each component (i.e., phylogenetic trees with short trunks and long branches). Truncal mutations, present across all tumor samples from a given patient, included known drivers of low-grade serous neoplasms: KRAS (G12D, n=4), BRAF (G469A, n=1), NF2 (n=1), and USP9X (n=1). Transformation to HGSC was associated with a TP53 mutation with bi-allelic inactivation in 3 cases, all with severe nuclear atypia, and associated with genome-wide copy number alterations and allelic imbalances. TP53-wildtype tumors comprised a morphologic spectrum, which included indeterminate-grade serous carcinomas with moderate nuclear atypia and high mitotic activity, while lacking extensive chromosomal instability (n=2), and poorly-differentiated carcinomas (n=2, including a high-grade Mullerian carcinoma and an undifferentiated carcinoma with sarcomatoid features). In summary, synchronous and metachronous low-grade serous neoplasms and higher-grade carcinomas are clonally related. Early genetic divergence, most evident in cases with TP53 mutations, suggests that high-grade transformation may be a relatively early molecular event.

High-grade Anaplastic Transformation of Ovarian Serous Borderline Tumor: A Distinctive Morphology With Abundant Dense Eosinophilic Cytoplasm and Dismal Prognosis

Ovarian serous borderline tumors (SBTs) have a generally favorable prognosis. Although the risk of progression to low-grade serous carcinoma is well documented, progression to high-grade carcinoma is rare. We report the clinicopathologic features of seven SBTs, each associated with the presence of a morphologically unique high-grade component with an extremely dismal prognosis. All of the SBTs exhibited typical hierarchical branching and scattered eosinophilic cells, whereas the high-grade component consisted of a profuse proliferation of epithelioid cells with abundant dense, eosinophilic cytoplasm, variable nuclear pleomorphism, and evident loss of WT1, estrogen receptor, and p16 positivity. In most cases, the SBT demonstrated an abrupt transition to the high-grade component, but one patient initially presented with the usual SBT and developed a recurrent disease that was composed entirely of the high-grade component. Targeted next-generation sequencing revealed identical driver mutations in both the SBT and high-grade components (BRAF in 3, KRAS in 1), confirming clonality. Three cases, in addition, harbored telomerase reverse transcriptase promoter mutations in both components. One case, despite insufficient material for sequencing, was BRAF V600E-positive by immunohistochemistry. Most patients with available follow-up data died within 9 months of diagnosis. This study confirms prior reports of ovarian SBT transformation to high-grade carcinoma and further characterizes a distinct subset with abundant dense eosinophilic cytoplasm and an extremely dismal prognosis. The presence of BRAF mutations in a major subset of these tumors questions the notion that BRAF is associated with senescent eosinophilic cells and improved outcomes in SBT. The role of the additional telomerase reverse transcriptase promoter mutations merits further investigation.

Molecular Pathology of Ovarian Epithelial Neoplasms: Predictive, Prognostic, and Emerging Biomarkers

This review focuses on the diagnostic, prognostic, and predictive molecular biomarkers in ovarian epithelial neoplasms in the context of their morphologic classifications. Currently, most clinically actionable molecular findings are reported in high-grade serous carcinomas; however, the data on less common tumor types are rapidly accelerating. Overall, the advances in genomic knowledge over the last decade highlight the significance of integrating molecular findings with morphology in ovarian epithelial tumors for a wide-range of clinical applications, from assistance in diagnosis to predicting response to therapy.

Primary Retroperitoneal Carcinomas: New Insights into Pathogenesis and Clinical Management in Comparison with Ovarian Carcinomas and Carcinoma of Unknown Primary

Primary retroperitoneal carcinomas are very rare tumors. Their pathogenesis remains unknown but may be associated with that of ovarian carcinomas, considering the similarity in morphology and gender preference. Although metaplasia of coelomic epithelium is the most widely accepted theory, the pathogenesis of retroperitoneal carcinomas may differ by histologic subtype, like ovarian carcinomas. Mucinous carcinoma, which develops in both women and men, may originate in both primordial germ cells and Walthard cell nests that may be derived from the fallopian tube. Serous carcinomas may be associated with endosalpingiosis, the presence of fallopian tube-like epithelium outside the fallopian tube, and a remnant Müllerian tract. Endometrioid and clear cell carcinomas appear to be associated with extraovarian endometriosis. Additionally, both carcinomas in the retroperitoneal lymph nodes may be metastatic diseases from endometrial and/or renal cell cancer that regress spontaneously (carcinoma of unknown primary). Retroperitoneal carcinomas are difficult to diagnose, as they have no characteristic symptoms and signs. Surgery is the cornerstone of treatment, but the necessity of chemotherapy may depend on histological subtype. Further studies are necessary, in particular studies on endosalpingiosis, as endosalpingiosis is a poorly understood condition, although it is associated with the development of both serous and mucinous carcinomas.

Borderline With Bad Behavior: An Unusual Low-grade Serous Carcinoma With Dedifferentiation From a Serous Borderline Tumor

The pathogenesis of serous ovarian tumors has been extensively investigated, with a dualistic model dividing these cancers into 2 groups. Type I tumors, including low-grade serous carcinoma, is characteristic for concurrent presence of borderline tumors, less atypical cytology, relatively indolent biologic behavior, and molecular aberrations related to the MAPK pathway with chromosomal stability. Meanwhile, type II tumors, such as high-grade serous carcinoma, are notable for no significant association with borderline tumors, higher grade cytology, more aggressive biologic behavior, and TP53 mutations along with chromosomal instability. We describe a case of morphologic low-grade serous carcinoma with focally increased cytologic atypia arising in serous borderline tumors involving both ovaries, which demonstrated highly aggressive behavior despite several years of surgical and chemotherapeutic management. Each recurrent specimen contained more uniform higher grade morphology than what was seen in the original specimen. Immunohistochemical and molecular studies in both the original tumor and the most recent recurrence demonstrate identical mutations in the MAPK genes, but with additional mutations in the latter, notably an acquisition of a variant of possible clinical significance in the SMARCA4 gene, which is associated with dedifferentiation and aggressive biologic behavior. This case challenges our current and still evolving understanding of the pathogenesis, biologic behavior, and expected clinical outcome of low-grade serous ovarian carcinomas. It also underscores the need for further investigation into this complicated tumor.

Molecular Pathology of Ovarian Epithelial Neoplasms: Predictive, Prognostic, and Emerging Biomarkers

This review focuses on the diagnostic, prognostic, and predictive molecular biomarkers in ovarian epithelial neoplasms in the context of their morphologic classifications. Currently, most clinically actionable molecular findings are reported in high-grade serous carcinomas; however, the data on less common tumor types are rapidly accelerating. Overall, the advances in genomic knowledge over the last decade highlight the significance of integrating molecular findings with morphology in ovarian epithelial tumors for a wide-range of clinical applications, from assistance in diagnosis to predicting response to therapy.

Clinicopathologic, Immunohistochemical, and Molecular Characteristics of Ovarian Serous Carcinoma With Mixed Morphologic Features of High-grade and Low-grade Serous Carcinoma

Despite the current classification of high-grade serous carcinoma (HGSCA) and low-grade serous carcinoma (LGSCA) as mutually exclusive diseases based on morphology and molecular pathogenesis, cases with mixed morphologic features of HGSCA and LGSCA have been reported. Herein we assess the clinicopathologic, immunohistochemical (IHC), and molecular genetic characteristics of a group of these cases, which we termed indeterminate grade serous carcinoma (IGSCA) in comparison with groups of HGSCA and LGSCA. Using the World Health Organization (WHO) classification criteria, we selected 27 LGSCA and 19 IGSCA for detailed morphologic study. Thirteen classic HGSCA, 19 classic LGSCA, and 19 IGSCA were selected for p53 and BRAF V600E IHC and molecular genetic testing by next-generation sequencing. IGSCA showed the architectural patterns of invasion of LGSCA, but with higher grade nuclear features focally and a mitotic index intermediate between LGSCA and HGSCA. Few cases in the IGSCA group showed mutant TP53 by IHC or sequencing (4/18, 22.2%), 1 case had mutant BRAF non-V600E by sequencing, and 1 had an NRAS mutation. When present, the mutations were identical in the low-grade and high-grade areas. The IGSCA group had a long-term survival similar to the classic HGSCA group. IGSCA with mixed morphologic features of HGSCA and LGSCA is a rare and potentially clinically aggressive variant of serous carcinoma. Their distinct morphologic, but heterogenous molecular features, including low frequency of TP53 and BRAF mutations suggest that these rare tumors may have a different pathogenesis pathway compared with classic HGSCA and classic LGSCA.

Clinicopathologic and Molecular Features of Paired Cases of Metachronous Ovarian Serous Borderline Tumor and Subsequent Serous Carcinoma

Although risk factors have been established for the development of serous carcinoma after a diagnosis of serous borderline tumor (SBT), comprising atypical proliferative serous tumor (APST) (ie, conventional SBT) and noninvasive low-grade serous carcinoma (niLGSC) (ie, micropapillary SBT), subsequent invasive carcinoma still occurs in a subset of women who are not at increased risk. Whether subsequent serous carcinoma in women with a prior SBT represents malignant progression/recurrence or an independent primary tumor is unclear, and the combined clinicopathologic and molecular features of SBTs and their subsequent carcinomas have not been fully characterized. In this study, we analyzed a cohort of 42 women initially diagnosed with SBT who subsequently developed serous carcinoma of a total of 1025 cases of ovarian SBT from a nationwide population-based cohort. Review of the diagnostic slides was performed from this subset of SBTs and matched metachronous invasive serous carcinomas (39 low grade, 3 high grade). DNA was extracted from tissue blocks available for 41 cases (both SBT and carcinoma, n=36; SBT only, n=3; carcinoma only, n=2). Samples were subjected to digital droplet PCR to analyze mutation hotspots in KRAS (codon 12) and BRAF (V600E), which are frequently found in low-grade serous tumors. Eighty-one percent of SBTs (34/42) were APST, and 19% (8/42) were niLGSC. Forty percent of cases (17/42) were FIGO stage I, the majority of which were APST (14/17; 82%). The median time to development of carcinoma was 9 years (range, 0.6 to 25 y). Mutations in SBTs were distributed as follows: 5/39 (13%) BRAF mutant, 22/39 (56%) KRAS mutant, and 12/39 (31%) wild-type for both genes. There was a significant relationship between SBT gene mutation and histologic type, with BRAF mutations occurring exclusively in APST and a higher frequency of niLGSC among SBTs wild-type for BRAF and KRAS (P=0.01). The diffuse presence of tumor cells with abundant eosinophilic cytoplasm was significantly associated with the BRAF mutation (P=0.001). Mutational analyses of matched SBT/carcinoma pairs revealed concordant profiles in 33/36 (92%) cases, of which 19 (53%) were KRAS mutant, 4 (11%) were BRAF mutant, and 10 (28%) were wild type for both genes. The 3 discordant cases consisted of a wild-type niLGSC with a subsequent BRAF-mutant invasive LGSC, a KRAS-mutant APST with a KRAS-mutant LGSC, and a BRAF-mutant APST with subsequent development of a KRAS-mutant high-grade serous carcinoma. In conclusion, some women with SBTs can subsequently develop serous carcinoma, occasionally over 10 years later. Most subsequent carcinomas are low grade, but a small subset can be high grade. The type of gene mutation in SBT correlates with various histologic features. While most cases of serous carcinoma developing after a diagnosis of SBT probably represent tumor progression, a minority are independent primary tumors, presumably arising from endosalpingiosis.

Low-grade serous ovarian cancer: State of the science

In January 2019, a group of basic, translational, and clinical investigators and patient advocates assembled in Miami, Florida, to discuss the current state of the science of low-grade serous carcinoma of the ovary or peritoneum-a rare ovarian cancer subtype that may arise de novo or following a diagnosis of serous borderline tumor. The purpose of the conference was to review current knowledge, discuss ongoing research by established researchers, and frame critical questions or issues for future directions. Following presentations and discussions, the primary objective was to initiate future collaborations, uniform database platforms, laboratory studies, and clinical trials to better understand this disease and to advance clinical care outside the boundaries of single academic institutions. This review summarizes the state of the science in five principal categories: epidemiology and patient outcomes, pathology, translational research, patient care and clinical trials, and patients' perspective.

Somatic genetic alterations in synchronous and metachronous low-grade serous tumours and high-grade carcinomas of the adnexa

AIMS

Low-grade serous carcinomas (LGSCs) and their precursors serous borderline tumours (SBTs) characteristically harbour mutations in BRAF, KRAS or NRAS but rarely in TP53, whereas high-grade serous carcinomas (HGSCs) are characterised by frequent TP53 mutations but rare BRAF, KRAS or NRAS mutations. In a small subset of cases, LGSCs and/or SBTs develop into high-grade tumours, including HGSCs and poorly differentiated carcinomas (PDCs). Here, we sought to define the repertoire of somatic genetic alterations in low-grade serous tumours and synchronous or metachronous high-grade adnexal carcinomas.

METHODS AND RESULTS

DNA extracted from five SBTs/LGSCs and synchronous or metachronous HGSCs/PDCs and matched normal tissue was subjected to massively parallel sequencing targeting all exons and selected non-coding regions of 341 cancer-related genes. The low-grade and high-grade tumours from a given case were related, and shared mutations and copy number alterations. Progression from low-grade to high-grade lesions was observed, and involved the acquisition of additional mutations and/or copy number alterations, or shifts from subclonal to clonal mutations. Only two (an HGSC and a PDC) of the five high-grade tumours investigated harboured TP53 mutations, whereas NRAS and KRAS hotspot mutations were seen in two HGSCs and one HGSC, respectively.

CONCLUSIONS

Our results suggest that progression from SBT to HGSC may take place in a subset of cases, and that at least some of the rare HGSCs lacking TP53 mutations may be derived from a low-grade serous precursor.

Pathogenesis, Genetics, and Genomics of Non-High Grade Serous Ovarian Cancers

The 5 main non-high grade serous epithelial ovarian cancers (clear cell, low grade endometrioid, low grade serous, mucinous, and carcinosarcoma) are discrete in terms of their pathogenesis, molecular biology, and treatment sensitivity. This article reviews the current understanding of their pathogenesis and molecular biology, highlighting areas of uncertainty where future research efforts should be focused.

Coexistence of BRAF V600E and TERT Promoter Mutations in Low-grade Serous Carcinoma of Ovary Recurring as Carcinosarcoma in a Lymph Node: Report of a Case

Low-grade serous carcinomas only rarely coexist with or progress to high-grade tumors. We present a case of low-grade serous carcinoma with transformation to carcinosarcoma on recurrence in the lymph node. Identical BRAF V600E and telomerase reverse transcriptase promoter mutations were identified in both the original and recurrent tumor. Given that telomerase reverse transcriptase promotor mutations are thought to play a role in progression of other tumor types, the function of telomerase reverse transcriptase mutations in BRAF mutated low-grade serous carcinoma deserves investigation.

Concurrent high-grade serous carcinoma and borderline tumor demonstrating different chemo-sensitivity

Ovarian high-grade serous adenocarcinoma responds well to regular platinum/taxane chemotherapy, while borderline tumor survives and demonstrates persistent disease. A 69-year-old Japanese woman was suspected for having advanced ovarian carcinoma. MRI showed cystic tumor containing solid component of the right adnexal region with massive ascites and peritoneal dissemination. Serum CA125 was elevated to 203 µ/ml; however, no remote metastases were detected. Laparotomy revealed that peritoneal carcinomatosis spreads out to omentum and subphrenic area. Omentum was partially removed with big tumor nodules that histologically demonstrated the high-grade serous adenocarcinoma with positive ascites cytology. After 6 cycles of postoperative chemotherapy with docetaxel and carboplatin, she received second surgery where the known residual bilateral adnexa and all of the persistent tumors were perfectly resected. Pathological examination of the tumor revealed serous borderline tumor with microinvasion and no evidence of residual high-grade serous carcinoma with negative ascites cytology. This is the extremely rare case of concurrent high-grade serous carcinoma and borderline tumor demonstrating differential chemo-sensitivity.

Serous Cystadenocarcinoma Arising in Presumed Vitelline Duct Remnant: A Case Report and Implications in the Management of Cancer of Unknown Primary

Background. Malignant neoplasms arising in Meckel's diverticulum, a vitelline duct remnant, are rare yet well-documented. Case Presentation. A 53-year-old previously healthy female presented with an enlarging midline abdominal wall mass. A computed tomography scan revealed a mass involving the linea alba, bilateral rectus abdominis, and subcutaneous fat. Extensive clinical workup failed to demonstrate other lesions, except local and paratracheal/hilar lymphadenopathy. Histopathologic examination of the resected tumor demonstrated a spectrum of serous neoplasia including serous cystadenoma, papillary serous carcinoma with numerous Psammoma bodies, and a poorly differentiated component. Immunophenotypically, the tumor cells were strongly positive for CK7, CK19, CA19.9, and MUC1 but negative for other lineage markers, findings suggestive of pancreatobiliary type differentiation. The patient died of the disease one year after the initial presentation despite chemotherapy, radiation, and surgery. Conclusion. We present a case of adenocarcinoma arising from the anterior midline abdominal wall, from presumed vitelline duct remnant, with histologic and immunophenotypic features of serous cystadenocarcinoma of pancreatobiliary origin. Though the origin from vitelline duct remnant is difficult to prove in this single case, understanding tumorigenesis of embryonic remnant origin is potentially important to improve the management of cancer of unknown primary.

Genomic classification of serous ovarian cancer with adjacent borderline differentiates RAS pathway and TP53-mutant tumors and identifies NRAS as an oncogenic driver

PURPOSE

Low-grade serous ovarian carcinomas (LGSC) are Ras pathway-mutated, TP53 wild-type, and frequently associated with borderline tumors. Patients with LGSCs respond poorly to platinum-based chemotherapy and may benefit from pathway-targeted agents. High-grade serous carcinomas (HGSC) are TP53-mutated and are thought to be rarely associated with borderline tumors. We sought to determine whether borderline histology associated with grade 2 or 3 carcinoma was an indicator of Ras mutation, and we explored the molecular relationship between coexisting invasive and borderline histologies.

EXPERIMENTAL DESIGN

We reviewed >1,200 patients and identified 102 serous carcinomas with adjacent borderline regions for analyses, including candidate mutation screening, copy number, and gene expression profiling.

RESULTS

We found a similar frequency of low, moderate, and high-grade carcinomas with coexisting borderline histology. BRAF/KRAS alterations were common in LGSC; however, we also found recurrent NRAS mutations. Whereas borderline tumors harbored BRAF/KRAS mutations, NRAS mutations were restricted to carcinomas, representing the first example of a Ras oncogene with an obligatory association with invasive serous cancer. Coexisting borderline and invasive components showed nearly identical genomic profiles. Grade 2 cases with coexisting borderline included tumors with molecular features of LGSC, whereas others were typical of HGSC. However, all grade 3 carcinomas with coexisting borderline histology were molecularly indistinguishable from typical HGSC.

CONCLUSION

Our findings suggest that NRAS is an oncogenic driver in serous ovarian tumors. We demonstrate that borderline histology is an unreliable predictor of Ras pathway aberration and underscore an important role for molecular classification in identifying patients that may benefit from targeted agents.

Type I to type II ovarian carcinoma progression: mutant Trp53 or Pik3ca confers a more aggressive tumor phenotype in a mouse model of ovarian cancer

A dualistic pathway model of ovarian carcinoma (OvCA) pathogenesis has been proposed: type I OvCAs are low grade, genetically stable, and relatively more indolent than type II OvCAs, most of which are high-grade serous carcinomas. Endometrioid OvCA (EOC) is a prototypical type I tumor, often harboring mutations that affect the Wnt and phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin signaling pathways. Molecular and histopathologic analyses indicate type I and II OvCAs share overlapping features, and a subset of EOCs may undergo type I→type II progression accompanied by acquisition of somatic TP53 or PIK3CA mutations. We used a murine model of EOC initiated by conditional inactivation of the Apc and Pten tumor suppressor genes to investigate mutant Trp53 or Pik3ca alleles as key drivers of type I→type II OvCA progression. In the mouse EOC model, the presence of somatic Trp53 or Pik3ca mutations resulted in shortened survival and more widespread metastasis. Activation of mutant Pik3ca alone had no demonstrable effect on the ovarian surface epithelium but resulted in papillary hyperplasia when coupled with Pten inactivation. Our findings indicate that the adverse prognosis associated with TP53 and PIK3CA mutations in human cancers can be functionally replicated in mouse models of type I→type II OvCA progression. Moreover, the models should represent a robust platform for assessment of the contributions of Trp53 or Pik3ca defects in the response of EOCs to conventional and targeted drugs.

Ovarian serous carcinoma associated with a distinct "corded and hyalinized" pattern

The "corded and hyalinized" pattern, described in endometrioid carcinoma, has not been previously reported in association with serous carcinoma. We describe a unique case of serous neoplasm of low malignant potential with low-grade serous carcinoma combined with a distinct pattern of high-grade carcinoma characterized by cords of epithelioid and spindled cells enmeshed in a hyalinized, collagenous stroma. This pattern was the predominant architecture in the patient's recurrence and caused a diagnostic challenge, as the splenic recurrence was initially diagnosed as a second primary high-grade spindle cell neoplasm. Both ovarian and splenic tumors displayed positive immunohistochemical staining for cytokeratin 7, cytokeratin 8/18, estrogen receptor, and paired box gene 8 (PAX-8) in the conventional serous carcinoma and the corded and hyalinized component, confirming the diagnosis of recurrent carcinoma. The behavior in this unique case of serous carcinoma associated with a distinct corded and hyalinized pattern was more aggressive than low-grade serous carcinoma, but more favorable than malignant mixed mullerian tumor.

Low-grade serous neoplasms of the ovary with transformation to high-grade carcinomas: a report of 3 cases

Ovarian borderline tumors usually occur in young patients and are associated with good clinical outcomes. A proportion of these tumors, particularly those with micropapillary features, may progress to low-grade serous carcinomas. Evolution of low-grade serous neoplasms to high-grade carcinomas is rare and infrequently reported. In this case report, we describe 3 cases of serous borderline tumor that progressed to high-grade carcinoma. Patient ages were 22, 35, and 47 yr. Two patients were initially diagnosed with ovarian serous borderline tumor, and recurred in the pelvis 3 and 10 yr later with sarcomatoid carcinoma. The third patient presented with low-grade serous carcinoma arising in a micropapillary serous borderline tumor, and recurred with a carcinosarcoma 3 yr later. All 3 patients had an aggressive clinical course: 2 died of disease and 1 patient has disease progression on chemotherapy. Occasional low-grade serous tumors of the ovary may transform to high-grade carcinomas, which can occur many years after initial diagnosis. The presence of a high-grade component significantly worsens patient outcomes.

Loss of p16INK4A expression in low-grade ovarian serous carcinomas

According to a tumor progression model, low-grade ovarian serous carcinomas may evolve from serous borderline tumors or micropapillary tumors. We sought to investigate the role of and associations between BRAF mutational status, extracellular signal regulated kinase activation, and p16(INK4A) expression in various types of ovarian serous tumors. We analyzed 29 typical ovarian serous borderline tumors, 8 micropapillary tumors, 4 low-grade invasive ovarian serous carcinomas, and 24 high-grade invasive ovarian serous carcinomas for the BRAF mutational status at codon 600; in addition, expression levels of the downstream signaling protein extracellular signal regulated kinase and the p16(INK4A) tumor suppressor protein were assessed by immunohistochemistry. There was a decline in p16(INK4A) expression from serous borderline tumors to micropapillary tumors with almost complete loss in low-grade invasive carcinomas. High-grade carcinomas had a variable p16(INK4A) expression pattern. We found a T1799A BRAF mutation in 12 typical serous borderline tumors (41%) and 1 micropapillary tumor (12.5%). No mutations were found in the low-grade and high-grade invasive carcinomas (0%). Among the typical borderline tumors, cases with BRAF mutations tended to have stronger p16(INK4A) expression compared with cases with wild-type BRAF. No other correlations were identified between the BRAF mutational status and expression levels of the analyzed proteins. Loss of p16(INK4A) expression may be a pathogenetic factor in the progression from serous borderline tumors to low-grade invasive carcinomas. The divergent molecular profiles support the theory that high-grade carcinomas are unrelated to serous borderline tumors or low-grade carcinomas.

High-Grade Serous Carcinoma Involving Fallopian Tube, Ovary and Peritoneum

The focus of this review is high-grade serous carcinoma (HGSC); for the purposes of this review, the term "pelvic SC" is used for HGSC that could be considered, based on historical definitions, to have arisen from ovary, fallopian tube, or peritoneum. These assignments of primary site are arbitrary and there is evidence that the distal fallopian tube is the site of origin of many pelvic HGSCs. The diagnosis of HGSC can be made readily based on routine histomorphologic examination in most cases; however, a variety of neoplasms can resemble HGSC. Thus, we review the key features of pelvic SC, current concepts of its pathogenesis, histopathological diagnostic criteria, discuss differential diagnosis, and review diagnostic ancillary studies that can be used in practice.