Advances in diagnosis, clinical management and molecular characterization of ovarian Brenner tumors

2.1 Clinical presentation and treatment

Benign Brenner tumors represent less than 5% of overall epithelial ovarian tumors and are often diagnosed as incidental findings in women in the fifth and sixth decades of life. Most patients are asymptomatic. Some patients might present with a unilateral large ovarian mass or endocrine symptoms with nonspecific laboratory results. Surgical management is an option if the mass is large and causes abdominal pain. A conservative approach for patients who desire preservation of fertility might be considered if the diagnosis is certain. The tumor is thought to have a benign clinical course with no risk of local recurrence.

2.2 Pathologic assessment and molecular analysis

Frequently unilateral, the lesion is macroscopically described to be well-circumscribed, solid, firm, and measures less than 2 ​cm with white or pale-yellow cut surfaces. Microscopically, they are characterized by sharply demarcated nests of transitional-type epithelium embedded in fibromatous stroma, some under cystic changes. Cytologic atypia or mitotic figures are generally not present. Up to 30% cases, metaplastic mucinous epithelium lines cystic nests.

Studies focusing on the molecular characterization of benign Brenner tumors mostly tried to clarify their histogenesis. Using a 358-gene targeted next generation sequencing panel, Tafe et al.⁴ identified amplification of MYC in three cases of benign Brenner tumors. MYC is a protooncogene whose encoded protein is a transcription factor involved in several metabolic pathways. MYC amplification has been reported in up to 25% of epithelial ovarian cancers, although no Brenner tumors were studied prior to this publication. This alteration appeared to co-occur with amplification of either CDK4 or CCND1. Cyclin D1 and cyclin-dependent kinases are key checkpoint proteins in the cell cycle regulation, and their amplification can lead to unchecked proliferation. MYC amplifications in benign Brenner tumors were found to be mutually exclusive with RAS mutations found in atypical proliferative (borderline) Brenner tumors, thus suggesting an alternative mechanism of pathway activation.

To determine whether there were potential molecular similarities of Brenner tumors to urothelial neoplasms, Khani et al. investigated whether the established mutations of urothelial carcinoma (C228T and C250T involving the TERT promoter region) were similarly demonstrated in a series of benign and malignant Brenner tumors.⁵ After PCR and Sanger sequencing methods, neither TERT promoter mutation C228T nor C250T were identified in fifteen benign cases of Brenner tumors (0/15), as well as malignant Brenner tumor cases (0/4), therefore suggesting that although Brenner tumors may have morphologic and immunophenotypic similarities to transitional epithelium, these two entities likely have distinct molecular pathogeneses.

3.1 Clinical presentation and treatment

Borderline Brenner tumors (BBTs) are even rarer than the benign counterpart. The median age of patients at diagnosis calculated from several studies is 60.4 years (range 30–84 years). Clinical presentation varies widely, including abdominal pain, abnormal uterine bleeding, and even as incidental findings. The role of serum biomarkers such as CA-125 is not well established. Conventional management consists of conservative or radical adnexal surgery, associated with peritoneal staging including peritoneal cytology, peritoneal biopsies, and omentectomy. Adjuvant chemotherapy is not recommended, as the prognosis is usually excellent with surgical treatment only. Few cases of invasive recurrence are described in the literature and are usually attributed to recurrence in the contralateral ovary, highlighting the need for careful follow-up if conservative management is pursued.⁶

3.2 Pathologic assessment and molecular analysis

BBTs commonly present as a unilateral adnexal mass with smooth surfaces, and either uni- or multiloculated with mixed cystic and solid areas. Histopathologically, they are characterized by epithelial mucinous or squamous metaplasia, the presence of small papillary processes, complex glandular formation, nuclear atypia, and increased mitotic activity. By definition stromal invasion is absent, and microinvasion and/or peritoneal implants have not been reported. Features of benign Brenner tumor are usually found in the background.

Alterations of the gene that encodes for p16 (CDKN2A) have been described in BBTs. Kuhn et al.⁷ investigated the presence of CDKN2A by using fluorescence in situ hybridization (FISH) and reported a homozygous deletion in the epithelial components of all seven atypical proliferative/borderline Brenner tumors, and absence of this deletion in corresponding benign Brenner tumors from their cohort. They suggested that the loss of CDKN2A expression could be involved in the progression from a benign to an atypical proliferative/borderline Brenner tumor, and that loss of expression of p16 by immunohistochemistry may be useful in distinguishing benign Brenner tumors from BBTs. In alignment with these findings, Ali et al.⁸ reported p16 immunohistochemical expression in three benign Brenner tumors, and absence of p16 in three BBTs and one malignant Brenner tumor. In the same study from Kuhn et al.,⁷ RAS pathway aberrations were also reported in three cases of BBTs (one KRAS and two PIK3CA somatic mutations). Additionally, Tafe et al.⁴ also detected RAS and PIK3CA mutations in two BBTs and did not identify alterations in the benign Brenner tumors. These findings may overall suggest that alterations in RAS genes, found only in BBTs, may play a role in the proliferative phenotype.

4.1 Clinical presentation and treatment

Malignant Brenner tumors (MBTs) is exceedingly rare and represent only 5% of all Brenner tumors. Usually diagnosed between the 5th-6th decades of life, the clinical presentation of women with MBTs is like other ovarian carcinomas. The most common symptoms include abdominal pain and distension, but some patients can experience postmenopausal bleeding, irregular menses, or no symptoms at all. The usage of tumors markers such as CA-125 has equivocal value: case series have reported abnormal values in 30%–54% of patients,^9,10 while a surveillance, epidemiology, and end results (SEER) database study reported abnormal values in 70% of patients.¹¹ There are no specific radiological features of MBTs on ultrasound, however the presence of an admixture of very low and hyperintense solid components on T2-weighted images on magnetic resonance imaging may suggest the transition to MBT. Amorphous calcifications can be seen in the solid component, while hemorrhage and necrosis are infrequent.

Conventional treatment for women with MBTs is surgical resection, with an attempt to achieve complete cytoreduction. Since 5% of women will have metastatic disease to the lymph nodes, the role of lymphadenectomy as the part of initial cytoreductive surgery is under discussion. Moreover, there was no survival advantage when comparing women who underwent lymphadenectomies compared to those who did not.¹¹ Furthermore, there is a low likelihood of nodal disease even when imaging may suggest a possible metastasis. In one study, six out of ten MBT patients with preoperative imaging suggestive of nodal disease failed to demonstrate the evidence of metastasis on pathologic examination of surgical specimens.¹² Despite these findings, it is generally recommended to resect suspicious nodes on preoperative imaging or during intraoperative assessment of the retroperitoneum.

Adjuvant carboplatin/taxane chemotherapy is recommended for patients with stage IC-IV disease. Limited data is available on the role of adjuvant chemotherapy for patients with stage IA-IB disease. In one study, three patients were observed after surgery: two women with stage IA and stage IB disease did not have recurrence, while one woman with stage IB disease recurred at 12 months.¹⁰ In another study, four women with stage IA disease were observed after surgery, with no recurrence at a median follow-up of 75 months. A fifth patient with stage IA disease received postoperative chemotherapy and was without recurrence at 8 months.⁹ In another report of four women with stage IA or IB disease, two received adjuvant chemotherapy and were without disease at 60 months, one was observed and without disease at 126 months, and one was lost to follow-up.¹² Based on these data, observation is recommended for women with stage IA MBTs (all grades) and for those with stage IB, grade 1 or 2 disease. Carboplatin/taxane is the preferred therapy of choice for women with stage IB, grade 3 disease.^12,13

The overall prognosis for women with stage I disease is excellent (5-year disease-specific survival (DSS): 95%) while those with stage II–IV disease have a 5-year DSS of 51%. Median time to recurrence is 11 months.¹⁴ The most common sites of recurrence are the peritoneal cavity and lung, with additional reports of recurrences in the dura, skin, and bone. Treatment for recurrences is typically similar to recurrences in other epithelial ovarian cancers, using similar agents that are platinum-sensitive and platinum-resistant. Chemotherapy for recurrences is unlikely to be curative; however, there have been reports of long-term survivals even in women with distant recurrences. The role of secondary cytoreductive surgery and radiation is unknown and should be considered on an individualized basis.

4.2 Pathologic assessment and molecular analysis

MBTs are usually unilateral with a median size of 10 ​cm, and they can be completely solid or cystic with mural nodules. They are composed of a frankly malignant component with an association with either benign or borderline counterparts. Microscopically, they are composed of nests of tumor cells with transitional-type epithelium that invades the ovarian stroma. The tumor cells show marked cytologic atypia with frequent mitotic activity, and areas of necrosis are common.

MBTs can histologically resemble solid, pseudoendometrioid and transitional cell carcinoma like (SET) ovarian serous carcinoma, endometrioid carcinoma, and careful pathologic review should be performed to distinguish the two entities since transitional cell carcinomas are high grade tumors that behave much more aggressively. Diagnosis of MBTs require the presence of both benign and malignant epithelial components with stromal invasion.

Recent studies have demonstrated that MBTs and ovarian carcinomas with transitional cell histology differ molecularly. The amplification of the MDM2 gene locus was discovered in three out of four MBTs, which was not found in three ovarian carcinomas with transitional cell histology.¹⁵ MDM2 plays a central role in regulating p53. It binds the protein and subsequently causes nuclear degradation, therefore acting as a tumor suppressor. Tumors (particularly sarcomas) overexpress MDM2 to impair the function of p53. A case report of MBT reported the same genetic findings (MDM2 amplification) and first reported the overexpression of MDM2 by immunohistochemistry (IHC).¹⁶ In the study by Shetty et al.,¹⁷ three out of four MBTs demonstrated increased (>25% of cells) MDM2 expression by IHC. The fourth case showed approximately 20% of cells to have strong nuclear MDM2 expression and was interpreted as equivocal. In two of three MDM2-IHC positive MBTs and in the single equivocal MBT, areas of borderline Brenner tumor were present, however did not stain for MDM2. All three cases of MBT with positive MDM2 expression by IHC showed MDM2 amplification by FISH (MDM2/CEP 12 ratios: 20.0/2.63 ​= ​7.6; 20.0/1.50 ​= ​13.3; and 19.20/1.85 ​= ​10.4), while the case with equivocal MDM2 expression was not amplified (MDM2/CEP 12 ratio: 2.13/2.20 ​= ​0.97). None of the benign and borderline Brenner tumors in the cohort showed MDM2 amplification by IHC or FISH. Interestingly, none of the high-grade serous carcinomas in this study showed positivity for MDM2 by IHC either, supporting the hypothesis that MDM2 amplification may be unique to the pathogenesis of Brenner tumors and may be used for the establishment of diagnoses.

Further characterization of the genomic profile of eleven MBTs was performed by Lin et al.¹⁸ The most frequently altered genes in MBTs were CDKN2A/B, which were inactivated via homozygous deletion in 55% (6 of 11) of cases, followed by activating FGFR3 alterations in 45.5% (5 of 11) of cases. One additional FGFR3 wild-type case (9%, 1 of 11) harbored an activating FGFR1 alteration, NM_023110:c.448 ​+ ​1 ​G ​> ​A_p.splice site 448 ​+ ​1G ​> ​A. This study showed that overall genomic alterations leading to activation of the FGFR pathway occurred in 55% (6 of 11) of malignant Brenner tumor cases. Activating PIK3CA mutations (E545K or C420R) co-occurred with FGFR3 alterations in three of five (60%) MBTs, while FGFR3 wild-type cases frequently exhibited alterations in MDM2 via amplification or inactivating TP53 mutations (R213*, R110P, R273H) in five of six (83%) cases. Composite biomarker analysis revealed that MBTs were microsatellite stable (11 of 11) and exhibited low tumor mutational burden (10 of 11), which are two well established biomarkers for immunotherapy. MBTs also exhibited no evidence of homologous recombination deficiency (HRD), which was assessed by genome-wide loss of heterozygosity score. The authors concluded that FGFR3 S249C may be specific to MBTs, and anti-FGFR inhibitors such as erdafitinib and pemigatinib may be useful in refractory, FGFR3-mutated MBTs.