Background

According to the 2020 WHO classification of female reproductive tumors, ovarian cancer is divided into serous carcinoma (SC), mucinous carcinoma (MC), endometrioid carcinoma (EC) and clear cell carcinoma (CCC) ^[1]. The proportion of high-grade serous carcinoma (HGSC) is 70%~80%, in which of low-grade serous carcinoma (LGSC) is less than 5%, EC is 10%, CCC is 10%, and MC is 3%. Carcinosarcoma and undifferentiated carcinoma are considered to be rare subtypes of ovarian cancer. The epithelial component is often HGSC, and the degree of malignancy is high ^[2]. Epithelial ovarian cancer (EOC) has a two-level classification system. Type I ovarian cancer includes LGSC, low-grade endometrioid carcinoma (LGEC), CCC and MC, accounting for 25% of ovarian cancer. These tumors usually develop slowly and tend to be genetically stable. The genes involved in mutations include KRAS, BRAF, etc. 75% of ovarian cancers belong to type II, including HGSC, high-grade endometrioid carcinoma (HGEC), etc. These tumors are highly aggressive, mostly advanced, and often show significant chromosomal instability and TP53 mutation^[3]. Because the molecular biology and prognosis of different histological subtypes of ovarian cancer are different, the detection and treatment methods that need to be performed should also be different.

Overview of Test Items

Homologous recombination repair (HRR) is the preferred repair method for DNA double-strand breaks. It is a complex signal transduction pathway involving multiple steps, involving dozens of genes including BRCA1/2^[4]. Homologous recombination deficiency (HRD) usually refers to the state of HRR dysfunction at the cellular level, which can be caused by many factors such as germline mutations, somatic mutations or epigenetic inactivation of HRR-related genes. HRD produces specific, quantifiable, and stable genomic alterations. The specific changes in the tumor genome described by HRD clinical detection are called "genomic scars", and loss of heterozygosity (LOH), telomere allele imbalance (TAI), large fragment shift (LST), etc. are regarded as genomic scars landmark. Patients with BRCA pathogenic gene mutations have a "synthetic lethal" effect with PARP inhibitors, and HRD detection can expand the potential benefit population of PARP inhibitors.

The NCCN guidelines recommend prioritizing detection of germline or systemic (g/sBRCA) mutations of the BRCA1/2 gene, and LOH or HRD status of tumor tissue. For relapsed patients, recommended tissue tests include but are not limited to BRCA1/2, HRD status, microsatellite instability (MSI)/mismatch repair (MMR) status, tumor mutational burden (TMB), BRAF, folate receptor α (FRα ), RET and NTRK and other biomarkers^[5]. For ovarian cancer staging/reduction surgery specimens, the CSCO guidelines class I recommend testing HRR pathway gene mutations such as g/sBRCA, and class III recommend testing HRD, MSI/MMR, and TMB^[2].

In addition to treatment-related markers, germline pathogenic mutations in HRR genes such as BRCA1/2, BRIP1, PALB2, RAD51C, and RAD51D have a clear correlation with the onset of ovarian cancer^[6]. The BRCA mutation rate in ovarian cancer patients is 22.3% (BRCA1 is 17.1%, BRCA2 is 5.3%), and the BRCA mutation rate in healthy people is only 0.4% (BRCA1 is 0.3%, BRCA2 is 0.1%) ^[7]. For BRCA1 and BRCA2 mutation carriers, the cumulative risk of developing ovarian cancer by age 80 is 44% and 17%, respectively ^[8]. BRCA1 mutation carriers have a 139.115-fold higher risk of developing ovarian cancer, and BRCA2 mutation carriers have a 74.926-fold higher risk ^[9]. Pathogenic mutations in the MMR gene are also associated with ovarian cancer. Both NCCN and CSCO guidelines recommend screening for Lynch syndrome^[2][6]. This article mainly analyzes the treatment-related markers, and the genetic testing related to hereditary tumors will not be repeated.

Applicability of HRD detection to patients with different histological subtypes

In recent years, PARP inhibitors have been widely used in the clinical practice of ovarian cancer, effectively prolonging the progression-free survival (PFS) of patients with advanced ovarian cancer, and changing the treatment pattern of ovarian cancer. A number of PARP inhibitors have been approved at home and abroad, and their indications for ovarian cancer have changed greatly in the past year: (1) Olaparib, Niraparib, and Rucaparib have been withdrawn successively. It is an indication for the treatment of multi-line recurrence of ovarian cancer, however the NCCN guidelines still recommend it, but the recommendation level has been lowered (2A to category 3); (2) Niraparib and Rucaparib have been withdrawn from patients with BRCA wild-type platinum-sensitive relapse Indications for maintenance therapy, the indications for maintenance therapy in patients with platinum-sensitive relapse of BRCA mutations are retained. See Table 1 for details.

Table 1 Ovarian cancer indications of PARP inhibitors^[5][10]

In order to understand the applicability of HRD detection (including BRCA mutation detection) to patients with different histological subtypes, the author extracted the data related to histological subtypes in the research entry and exclusion criteria from the Clinical Trails database and the main literature published in drug clinical research. Information, made into Table 2.

Table 2 Inclusion and exclusion criteria for clinical research of PARP inhibitors in ovarian cancer ^[11-20]

It is not difficult to see from Table 2 that most of the histological subtypes included in clinical studies of PARP inhibitor ovarian cancer are HGSC, HGEC; there are also a small number of mixed cancers, CCC and undifferentiated cancers. LGSC and LGEC are basically not included in clinical research, while MC is often included in the exclusion criteria.

Brief analysis of other markers

About 3% of HGSC are caused by MMR gene mutations ^[21]. Although the proportion of MMR-deficient tumors is not high in EOC as a whole, it accounts for as high as 13% in EC^[1]. The NCCN guidelines recommend that patients with all EC subtypes be tested for MSI/MMR at the stage of pathological diagnosis ^[5]. MSI/MMR is an important companion diagnostic marker for immune checkpoint inhibitors (ICIs). There are a number of ICIs approved for pan-solid tumors at home and abroad that can be used for the treatment of ovarian cancer. The Keynote158 study included 15 patients with ovarian cancer, and the objective response rate (ORR) was 33.3%, of which 3 cases achieved complete remission (CR) and 2 cases achieved partial remission (PR) ^[22]. Two patients with ovarian cancer were included in the GARNET study of Dostarlimab (DOR) of more than 25.1 months ^[10]. Four ICIs have been approved for pan-solid tumor indications in China, among which the RATIONALE-209 study of Tislelizumab included a patient with ovarian cancer and achieved PR; the clinical study of Serplulimab (NCT03941574) included a case of fallopian tube Cancer patients also achieved PR^[23].

As an emerging biomarker, TMB has been paid more and more attention to its role in predicting the efficacy of tumor immunotherapy. However, its role in ovarian cancer is still unclear, and patients with ovarian cancer were not included in the prospective TMB analysis of Keynote158 ^[24].

On November 14, the FDA approved the antibody-drug conjugate Mirvetuximab Soravtansine-gynx for FRα-positive, platinum-resistant EOC, fallopian tube cancer, or primary peritoneal cancer that has received one to three systemic therapies ^[10]. The NCCN guidelines have also updated this recommendation ^[5]. However, its Study 0417 only included HGSC patients, and patients with endometrioid, clear cell, mucinous or sarcomatoid histology, mixed tumors containing these histologies, and low-grade/borderline ovarian tumors were all excluded^[11] .

NTRK, RET, and BRAF are all companion diagnostic markers for targeted therapy in pan-solid tumors. No patients with ovarian cancer were included in the approved clinical study of the NTRK inhibitor Larotrectinib; two patients with gynecological tumors were included in the study of Entrectinib, one of which was ovarian cancer[10][25]. In the LIBRETTO-001 study of the RET inhibitor Selpercatinib, a patient with ovarian cancer was enrolled and achieved a PR with a median DOR of 14.5 months ^[26]. However, the ARROW study of another RET inhibitor, Pralsetinib, also included a patient with ovarian cancer, and the results progressed ^[27]. Although the above drugs, except Pralsetinib, have been approved for pan-cancer indications and are recommended by the guidelines, it is difficult to prove their actual curative effect on ovarian cancer patients due to the small number of cases included in the study.

BRAF mutation is an important molecular mechanism of LGSC. In the BRF117019 and NCI-MATCH ArmH studies of Dabrafenib combined with Trametinib, 5 cases of LGSC and 1 case of mucinous-papillary serous peritoneal adenocarcinoma were included, and the ORR of 6 cases of gynecological tumors reached 83.3%^[10]. The NCCN guidelines also recommend Trametinib and Binimetinib for targeted therapy of recurrent LGSC ^[5]. The reason for the recommendation is given in the popular article "Molecular Mechanism and Targeted Therapy of Low-Grade Serous Ovarian Cancer".

Conlcusion

1. Based on the above various evidences, combined with the recommendations of the guidelines, the author summarizes the genetic tests that can be performed in patients with common histological subtypes of ovarian cancer. The following is only the author's personal understanding and does not represent authoritative opinions.

Patients with ovarian cancer, fallopian tube cancer, and primary peritoneal cancer should undergo genetic risk assessment and g/sBRCA detection^[5].

2. For stage III/IV HGSC patients, HRD testing is recommended. Since HRD often includes BRCA detection, it is recommended that if possible patients should do the direct detection of HRD. For recurrent HGSC patients, it is recommended to increase the detection of FRα expression (mainly immunohistochemical method at present), and MSI/MMR is also an item that can be considered.

3. BRAF V600E detection is recommended for LGSC patients. The role of HRD testing may be limited.

4. MSI/MMR testing is recommended for all patients with EC histology. For patients with G2/3 EC in stage III/IV, it is recommended to detect HRD. For patients with G1 EC, the role of HRD testing may be limited.

5. For patients with carcinosarcoma and CCC, HRD detection may suggest the benefit of PARP inhibitors.

6. Routine testing is recommended for patients with MC.

7. Recurrent patients may consider detecting TMB, NTRK, RET, BRAF and other biomarkers to find opportunities for treatment; for newly diagnosed patients, the significance of detecting these markers may be limited.

Spacegen’s HRD detection uses specific heterozygous SNP sites, evenly covers the entire human genome, and comprehensively analyzes the three major genomic scar markers of LOH, TAI, and LST. Simultaneously detect HRR and MMR-related genes, assess HRD and genetic risk at the systemic and germline levels. 

References

[1] 2020 WHO classification of female reproductive tumors

[2] CSCO Ovarian Cancer Diagnosis and Treatment Guidelines 2022

[3] Principles of Molecular Diagnosis and Individualized Tumor Therapy 

[4] Life Sci. 2020 Nov 15;261:118434.

[5] NCCN guidelines for clinical diagnosis and treatment of ovarian cancer, fallopian tube cancer and primary peritoneal cancer 2023 v1

[6] NCCN hereditary/familial breast cancer, ovarian cancer, pancreatic cancer high risk assessment 2023 v1

[7] Gynecol Oncol. 2018 Oct; 151(1): 145-152.

[8] JAMA. 2017 Jun 20; 317(23): 2402-2416.

[9] Cancer.2015 Jan15; 121(2): 269-75.

[10] FDA official website data

[11] Clinical Trails

[12] N Engl J Med. 2018 Dec 27; 379(26): 2495-2505.

[13] N Engl J Med. 2019 Dec 19; 381(25): 2416-2428.

[14] N Engl J Med. 2019 Dec 19;381(25):2391-2402.

[15] Lancet Oncol. 2017 Sep;18(9):1274-1284.

[16] N Engl J Med. 2012 Apr 12;366(15):1382-92.

[17] N Engl J Med. 2016 Dec 1;375(22):2154-2164.

[18] Lancet.2017 Oct 28;390(10106):1949-1961.

[19] Lancet Oncol. 2019 May;20(5):636-648.

[20] Int J Gynecol Cancer. 2019 Nov;29(9):1396-1404.

[21] Cancer Discov. 2015 Nov;5(11):1137-54.

[22] J Clin Oncol. 2020 Jan 1;38(1):1-10.

[23] Br J Cancer. 2022 Dec;127(12):2241-2248.

[24] Lancet Oncol. 2020 Oct;21(10):1353-1365.

[25] Lancet Oncol. 2020 Feb;21(2):271-282.

[26] Lancet Oncol. 2022 Oct;23(10):1261-1273.

[27] Nat Med. 2022 Aug;28(8):1640-1645.