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. Author manuscript; available in PMC: 2022 May 1.
Published in final edited form as: Gynecol Oncol. 2021 Mar 3;161(2):545–552. doi: 10.1016/j.ygyno.2021.02.028

Molecular Characterization of High-Grade Serous Ovarian Cancers Occurring in Younger and Older Women

Olga T Filippova a,#1, Pier Selenica b,#1, Fresia Pareja b, Mahsa Vahdatinia b, Yingjie Zhu b, Xin Pei c, Nadeem Riaz c, Kara Long Roche a, Dennis S Chi a, Nadeem R Abu-Rustum a, Lora H Ellenson b, Jorge S Reis-Filho b, Dmitriy Zamarin d, Britta Weigelt b,*
PMCID: PMC8240481  NIHMSID: NIHMS1677907  PMID: 33674143

Abstract

Objectives:

To determine if the mutational landscapes and genomic features of homologous recombination DNA repair defects (HRD) vary between younger and older patients with high-grade serous ovarian cancer (HGSOC).

Methods:

Younger and older women were defined as bottom and top age quartiles, respectively. HGSOCs from 15 younger (median 49 years, range 35-53) and 15 older women (median 72 years, range 70-87) were subjected to whole-exome sequencing (WES). For validation, HGSOC WES data were obtained from The Cancer Genome Atlas (TCGA), including 38 younger (median 45 years, range 34-50) and 30 older women (median 74 years, range 68-84). Mutational profiles, BRCA1/2 status, genomic HRD features, and for TCGA cases RNA-sequencing-based HRD transcriptomic signatures were assessed.

Results:

In the institutional cohort, pathogenic germline BRCA1/2 mutations were more frequent in younger (5/15) than older women (0/15, p=0.042). No somatic BRCA1/2 mutations were identified. HGSOCs from older patients preferentially displayed aging-related mutational signatures and, in contrast to younger patients, harbored CCNE1 amplifications (3/15, 20%). In the TCGA cohort, pathogenic germline BRCA1 (younger 8/38, older 0/30, p=0.007) but not BRCA2 mutations (young 3/38, older 4/30, p=0.691) were more frequent in younger patients. Again, no somatic BRCA1/2 mutations were identified. HGSOCs from younger women more frequently displayed genomic features of HRD (all, p<0.05), a significant HRD gene-signature enrichment, but less frequently CCNE1 amplification (p=0.05). Immunoreactive CLOVAR subtypes were more common in HGSOCs from younger women, and proliferative subtypes in HGSOCs from older women (p=0.041).

Conclusions:

HGSOC patients diagnosed at an older age less frequently harbor pathogenic BRCA1 germline mutations and genomic features of HRD than younger women. Individualized treatment options, particularly pertaining to use of PARP inhibitors, in older women may be warranted.

Keywords: Ovarian cancer, extreme of ages, molecular profiles, BRCA1/2, homologous recombination DNA repair deficiency, PARP inhibitor

1. INTRODUCTION

Ovarian cancer continues to be the deadliest gynecologic malignancy, and the fifth leading cause of all cancer deaths in women, with 21,750 new cases and 13,940 deaths estimated for 2020 in the U.S.1 As a group, high-grade serous ovarian cancers (HGSOCs), which constitute approximately 70% of epithelial ovarian cancers, are characterized by recurrent mutations in TP53, BRCA1 and BRCA2, and alterations in other homologous recombination DNA repair (HR) genes.2-4 Germline and somatic BRCA1 and BRCA2 mutations are found in approximately 23% and 7% of HGSOCs, respectively,3 although the reported rates vary greatly due to patient selection and scope of testing, and the true prevalence of both germline and somatic BRCA1/2 mutations in this population remains unknown.5 In addition, BRCA1 promoter methylation has been found in 11% of HGSOCs in The Cancer Genome Atlas (TCGA) study.3,4 Loss of heterozygosity (LOH) is seen in the majority of tumors bearing BRCA mutations, 81% for BRCA1 and 72% for BRCA23,6

Approximately 50% of HGSOCs exhibit evidence of homologous recombination deficiency (HRD), with alterations across a variety of genes/pathways in addition to BRCA1 and BRCA2, including Fanconi Anemia genes (e.g. PALB2), RAD genes (e.g. RAD51B, RAD51C, RAD51D and RAD50), BRIP1, and BARD1.2-4 Three quantitative metrics are currently being used commercially for determining HRD, (1) telomeric allelic imbalance (TAI), or the number of sub-chromosomal regions with allelic imbalance extending to the telomere; (2) whole genome tumor LOH, or presence of a single allele, and (3) large-scale state transition (LST) scores, which quantifies the number of chromosomal breaks between adjacent regions of at least 10Mb.2,3 These three metrics are combined together for an overall HRD score, each having an equal weight, however, different cut-offs have been used across trials7-10 and no standardized HRD high vs low score has been established as yet.2

Recent results of four large randomized trials have demonstrated improvement in progression free survival (PFS) for women treated with poly (ADP-ribose) polymerase (PARP) inhibitors in the upfront setting, with the most robust improvement in women with germline or somatic BRCA1/2 mutations or those with tumors deemed HRD.7-10 Approvals for PARP inhibitor maintenance therapy include all patients, irrespective of HRD status, and not all patients with ovarian cancer undergo HRD testing. Furthermore, PARP inhibitor therapy may predispose patients to unnecessary toxicities, in particular in older adults.11

The median age of diagnosis for women with HGSOC is 63 years, however, the disease is diagnosed in women of all ages.12 The genomic profiles of HGSOC, in particular the frequency of genomic features of HRD, across specific age groups remains unexplored. The aim of this study was to define whether the mutational landscapes, the frequency of genomic features of HRD and mutations affecting core HR genes, and HRD gene expression signatures would be distinct in HGSOC patients at the extremes of age.

2. METHODS

2.1. Case selection

Two cohorts of women with HGSOC were included in this study. For each cohort, women were stratified by age, comparing “younger” women, defined as those in the bottom age quartile at the time of diagnosis, to “older” women, defined as those in the top age quartile.

Cohort 1: This study was approved by the Institutional Review Board (IRB) of Memorial Sloan Kettering Cancer Center (MSK). All patients treated for advanced stage epithelial ovarian cancer between January 2016 and January 2019 were identified from a prospectively maintained database, and this list was used to define the age at diagnosis for “younger” and “older” women of cohort 1. Younger (n=15) and older (n=15) cases were matched by 2014 International Federation of Gynecology and Obstetrics (FIGO) stage III or IV, high-grade serous histology, and treatment with optimal (residual disease ≤1cm) upfront primary debulking surgery (PDS) followed by 6 cycles of post-operative carboplatin/paclitaxel chemotherapy. Representative hematoxylin and eosin (H&E)-stained sections of each HGSOC were rereviewed by a gynecologic pathologist (LHE). Clinical data and germline mutations, including BRCA1 and BRCA2 status, were abstracted from the electronic medical record.

Cohort 2: Publicly available whole-exome sequencing data of HGSOCs from TCGA were obtained.4 Clinical data of a curated list of 585 HGSOCs4 were obtained from cBioPortal13,14 and used to define the younger and older age at diagnosis cut-offs, and younger (n=38) and older (n=30) were matched by FIGO stage (III or IV) and high-grade serous histology. Whole-exome sequencing-derived MC3 mutational data15 were obtained from cBioPortal.13,14

2.2. Massively parallel sequencing analysis

Following review by two pathologists (FP and MV), DNA extracted from microdissected tumor and normal tissues from 15 younger and 15 older cases were subjected to whole-exome sequencing at the MSK Integrated Genomics Operation (IGO) using validated protocols, as previously described.16,17 Sequencing data were analyzed as previously described.16,17 In brief, somatic single nucleotide variants (SNVs) were detected by MuTect (v1.0), small insertion and deletions (indels) by Strelka (v2.0.15), VarScan2 (v2.3.7), Lancet (v1.0.0), Scalpel (v0.5.3) and Platypus.18-23 Mutations affecting hotspot codons were annotated according to Chang et al.24 Copy number alterations (CNAs) and loss of heterozygosity (LOH) were defined using FACETS25 as previously described.16,17

2.3. Genomics features of HRD

For the MSK cohort, large-scale state transition (LST) scores, the number of small insertions and deletions, deletion microhomology, median deletion length and mutations, and mutational signatures were defined for all cases, whereas for HGSOCs from TCGA, these HRD genomic features were retrieved from Riaz et al.6 Here and in Riaz et al.,6 the levels of LSTs, representative of genomic scars indicative of HRD, were assessed as previously described.6,26,27 The length of small deletions (indels) and microhomology scores were assessed in the HGSOCs as reported in Alexandrov et al28, as HRD cancers are enriched for deletions ≥5bp and indels with ≥3bp of microhomology on each side of the indel.27,28 Mutational signatures were inferred from non-synonymous and synonymous mutations in a given HGSOC using deconstructSigs29-31 at default parameters, as previously described.27 Finally, the presence of bi-allelic pathogenic mutations in a curated list of 102 HR-related DNA repair genes6 was assessed (cohort 1) or obtained from Riaz et al6 (cohort 2).

2.4. Gene signature analysis

RNA-sequencing data were available for 30/38 younger and 23/30 older HGSOCs cases included in the TCGA cohort and were obtained from the NIH GDC Data Portal (https://portal.gdc.cancer.gov/). Genes with absent or low gene expression levels across samples, defined as the total number of raw read counts less than 50, were excluded from further analyses. The status of the 230 gene HRD transcriptomic signature described by Peng et al32 was assessed through single-sample Gene Set Enrichment Analysis (ssGSEA). ssGSEA scores were calculated for a given sample using gsva33 ‘ssgsea’ method based on the RNA-sequencing FPKM values. Furthermore, the “Classification of Ovarian Cancer” (CLOVAR) gene expression signatures/ subtypes were obtained for each HGSOC in the TCGA cohort from Verhaak et al.34

2.5. Statistical analyses

Comparisons of LST scores, median deletion length and other continuous variables were performed using Mann-Whitney U test. Comparison of mutational signatures, frequency of germline BRCA mutations and other nominal variables was done using Fisher’s exact tests, two tailed. Progression-free survival (PFS) was generated using the Kaplan-Meier method and compared by log-rank test. A p-value of <0.05 was considered statistically significant. All statistical analyses were performed using IBM SPSS v24.0.0.0.

3. RESULTS

3.1. Clinical features of HGSOCs diagnosed in younger vs older women

We subjected HGSOCs from patients at the extremes of ages at diagnosis to whole-exome sequencing analyses. The median age at diagnosis of the 15 younger patients was 49 years (range 35 – 53 years) and of the 15 older women 72 years (range 70 – 87 years).

Of these 15 younger women, 10 underwent complete gross resection (CGR) during upfront primary debulking surgery (PDS), whereas 5 had residual disease between 0.1 and 1cm. After a median follow-up of 26 months, 9 younger women recurred, with a median PFS of 19.2 months. Of the 15 older women, CGR was achieved in 10 during PDS, whilst the other 5 has residual disease between 0.1 and 1cm. After a median follow-up of 27 months, 8 older women recurred, with a median PFS of 21.0 months. The median PFS of younger and older women with HGSOC was not statistically different (p=0.766). No patients expired during the follow-up time.

3.2. Genomic features of HRD in HGSOCs diagnosed in younger vs older women

As expected, TP53 was the most recurrently mutated gene in both the younger (100%) and older (87%) histologically confirmed HGSOC patients. TP53 hotspot mutations were more common in HGSOCs of the younger age cohort (13/15 young, 87% vs 7/15 old, 47%, p=0.05, Fisher’s exact test), whereas TP53 indels were more common in HGSOCs from older patients, although this was not statistically significant (2/15 young, 13% vs 5/15 old, 33%, p=0.39, Fisher’s exact test; Figure 1). Furthermore, the total mutation burden between younger (median 86, range 27-360) and older women with HGSOC (median 83, range 56-227) was similar (p=0.885, Figure 2), and no differences in the genes recurrently mutated were identified between the two age groups. We noted, however, that CCNE1 amplification was detected in three HGSOCs from older patients (20%) but in none of the HGSOCs patients in the younger cohort (0%; p=0.22; Fisher’s exact test, Figure 1).

Figure 1. Repertoire of somatic mutations in advanced stage high-grade serous ovarian carcinomas occurring in younger and older patients (MSK cohort).

Figure 1.

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Non-synonymous somatic mutations and CCNE1 amplification identified by whole-exome sequencing, clinically identified germline BRCA1 and BRCA2 mutations and dominant mutational signatures in high-grade serous ovarian cancers occurring in younger (n=15) and older (n=15) women (MSK cohort). Cases are represented by columns and genes by rows. Mutations present in ≥3 cases are shown. Mutation types, dominant mutational signature, and germline BRCA1/2 status are color-coded according to the legend. Percentages in bold, statistically significantly different. *, p-value=0.042, Fisher’s exact test. SNV, single nucleotide variant; HRD, homologous recombination deficiency.

Figure 2. Genomic features of homologous recombination DNA repair deficiency in high-grade serous ovarian cancers occurring in younger and older women (MSK cohort).

Figure 2.

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A, median age at diagnosis (years), and rates of clinically identified germline BRCA1 and BRCA2 mutations (combined for comparison; Fisher’s exact test), B, large-scale state transition (LST) scores, C, number of small insertions and deletions, D, number of deletions with microhomology, E, median deletion length, F, mutational signatures, and G, total number of somatic mutations in HGSOCs from younger (n=15) and older (n=15) women subjected to whole-exome sequencing (MSK cohort). p-values in B-G, Mann-Whitney U test. HRD, homologous recombination deficiency.

Pathogenic BRCA1 and BRCA2 germline mutations were present in three (20%) and two (13%) of the younger women with HGSOC, respectively, whereas none of the older women harbored BRCA1 or BRCA2 germline mutations (p=0.042, Fisher’s exact test, Figures 1 and 2A). No pathogenic somatic BRCA1/2 mutations were identified in the HGSOCs analyzed. Germline mutations in HR genes other than BRCA1/2 were not identified in the younger women, but a mono-allelic pathogenic PALB2 germline mutation was present in one older patient. No other bi-allelic mutations in HR-related genes were identified in either group.

Upon assessment of other genomic features of HRD, we found that HGSOCs in younger women had numerically higher LST scores (median 29, range 14-43) than older women (median 20, range 0-46; Figure 2B), a lower number of small insertions and deletions (median 3, range 1-11) than older women (median 5, range 0-23; Figure 2C) and a lower number of deletions with microhomology (median 0, range 0-4) than older women (median 1, range 0-4; Figure 2D), however none of these reached statistical significance, likely due to the limited number of cases examined. We further observed that the median deletion length was similar in HGSOCs from younger patients (median 4.5, range 0-20) and older patients (median 3, range 0-12.5; p=0.133, Figure 2E). Whilst the majority of HSGOCs from younger patients (10/15, 67%) displayed a dominant mutational signature 3 associated with HRD, only 4/15 (27%) of HGSOCs from older patients did (p=0.066, Figure 2F).

Given the observed difference in the frequency of BRCA1/2 mutations in HGSOCs from younger vs older women, and the trends toward a higher prevalence of HRD in women at the younger than the older end of the age spectrum, we next sought to investigate these findings in a larger series of HGSOCs. As a validation dataset we used whole-exome sequencing-derived data from HGSOCs from 38 younger and 30 older patients from TCGA,4,6 matched for stage (2014 FIGO stage III or IV) and high-grade serous histology. The median age at diagnosis of the younger women was 45 years (range 34 – 50 years) and of the older women 74 years (range 68 – 84 years; Figure 3A). There were no statistical differences between the age distributions in the MSK and TCGA cohorts (MSK vs TCGA young, p=0.238 and MSK vs TCGA old, p=0.430, Mann-Whitney U test).

Figure 3. Genomic features of homologous recombination DNA repair deficiency in high-grade serous ovarian cancers occurring in younger and older women from TCGA.

Figure 3.

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A, median age at diagnosis (years), and rates of clinically identified germline BRCA1 and BRCA2 mutations (combined for comparison; Fisher’s exact test), B, large-scale state transition (LST) scores, C, number of small insertions and deletions, D, number of deletions with microhomology, E, median deletion length, F, mutational signatures, and G, total number of somatic mutations, in HGSOCs from younger (n=38) and older (n=30) women from TCGA (Nature 20114) H, Homologous recombination defect (HRD) gene signature enrichment32 in HGSOCs from younger (n=30) and older (n=23) women with available RNA-Sequencing data from TCGA. H, Classification of HGSOCs from younger (n=38) and older (n=30) women into the Ovarian Cancer (CLOVAR) survival gene signatures/ subtypes (Verhaak et al, 201334). ssGSEA, single sample gene set enrichment analysis. p-values in B-G, Mann-Whitney U test, and in H, Chi square.

Akin to the MSK cohort, the mutational burden was similar between older (median 118.5, range 30-342) and younger patients (median 103, range 48-327, p=0.97, Figure 3G). TP53 somatic mutations were the most common mutations observed (young 35/38, 92%, older 28/30, 93%, Figure 4), although in the TCGA cohort, the number of hotspot mutations was similar between the two age groups (31/38 vs 21/27, p=0.760). As in the MSK cohort, no other recurrent somatic mutations were identified to be distinct between HGSOCs in younger vs older women.

Figure 4. Repertoire of somatic mutations in advanced stage high-grade serous ovarian carcinomas occurring in younger and older women from TCGA.

Figure 4.

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Non-synonymous somatic mutations and CCNE1 amplification identified by whole-exome sequencing (TCGA, MC3 data, obtained from cBioPortal13,14), germline BRCA1 and BRCA2 mutations (Riaz et al6), dominant mutational signatures, and Classification of Ovarian Cancer (CLOVAR) survival gene expression signatures/ subtypes in high-grade serous ovarian cancers occurring in younger (n=38) and older (n=30) women from The Cancer Genome Atlas (TCGA) ovarian cancer study (Nature 20114). Cases are represented by columns and genes by rows. Mutations present in ≥5 cases are shown. Mutation types, dominant mutational signature, CLOVAR survival signature/ subtype, and germline BRCA1/2 status are color-coded according to the legend. Percentages in bold, statistically significantly different. *, p-value=0.028, Fisher’s exact test. SNV, single nucleotide variant; HRD, homologous recombination deficiency.

Next, we assessed the frequency of pathogenic BRCA1/2 mutations in the different age groups, which were more frequent in the younger cohort (p=0.028). Of the 38 younger women, 8 (21%) harbored pathogenic BRCA1 germline mutations and 7 (18%) had pathogenic BRCA2 germline mutations, whereas none of the older women had BRCA1 germline mutation and only 4 harbored BRCA2 germline pathogenic mutations (Figures 3A and 4). No additional somatic or germline bi-allelic pathogenic mutations affecting HR-related genes were identified in this cohort, including somatic BRCA1 or BRCA2 mutations. CCNE1 amplifications were present in HGSOCs of 3/38 younger patients (8%) but were found to be more frequent in older patients (8/30, 27%, p=0.05; Fisher’s exact test), in support of the findings from the analysis of the MSK cohort. We also observed that in HGSOCs from younger women, 2/3 CCNE1 amplifications cooccurred with BRCA1/2 germline alterations, whereas all 8 CCNE1 amplifications were distributed in a mutually exclusive pattern with BRCA1/2 germline alterations in HGSOCs of older women (Figure 4).

All genomic features of HRD assessed in the TCGA cohort were significantly different between HGSOCs occurring in younger versus in older women. Specifically, LST scores were higher in HGSOCs in younger women (median 31, range 2-46) than in older women (median 20, range 5-42, p=0.012, Figure 3B). The number of small insertions and deletions (young median 4.5, range 0-17, older median 2, range 0-10, p=0.005, Figure 3C) as well as the number of deletions with microhomology (younger median 3, range 9-13, older median 1, range 0-5, p=0.001, Figure 3D) were statistically higher in the HGSOCs of the younger cohort. The median deletion length was also higher in younger (median 2.5, range, 0-24) than in older women (median=1, range 1-13.5, p=0.005, Figure 3E). Additionally, the majority of HGSOCs from younger women displayed a dominant HRD-associated mutational signature 3 (25/38, 66%) in comparison to only 12/30 (40%) of older patients displaying this signature. The majority of older patients had a dominant mutational signature 1 (17/30, 57%) associated with aging, as compared to HGSOCs occurring in younger patients (5/38, 13%, p=0.0004, Figure 3F). These data were confirmed at the transcriptomic level. We observed a significantly greater enrichment of an HRD gene expression signature described by Peng et al32 in the HGSOCs of younger than of older women from the TCGA cohort (median ssGSEA score 1.63 vs 1.40, p=0.0111, Mann-Whitney U test; Figure 3H).

Finally, we assessed the distribution of the “Classification of Ovarian Cancer” (CLOVAR) survival signatures/ subtypes in the TCGA HGSOCs.34 There was a statistically significant difference (p=0.041, Chi Squared test) in the frequency of CLOVAR survival signatures/ subtypes (Figure 3I)34; while the frequency of differentiated (9/38, 24% vs 10/30, 33%) and mesenchymal (11/38, 29% vs 6/30, 20%) CLOVAR subtypes was similar between HGSOCs from younger and older women in the TCGA cohort, the immunoreactive CLOVAR subtype was significantly more common in HGSOCs of younger women (11/38, 29% vs 2/30, 7%, p=0.02) and the proliferative CLOVAR subtype in older women (7/38, 18% vs 12/30, 40%, p=0.049). All four CLOVAR survival signatures were found in HGSOCs from patients with germline BRCA1/2 mutations (Figure 4).

4. DISCUSSION

HGSOC is a disease that afflicts women of all ages, however little is known about the genomic differences in women across age strata. Here, we demonstrate important differences in the mutational landscape and frequency of HRD genomic features and gene expression signatures in HGSOC patients at the “younger” and “older” ends of the age spectrum. Older HGSOC patients less frequently harbor BRCA1 germline mutations than patients in the younger end of the age spectrum. HGSOCs affecting younger patients more frequently displayed genomics features of HRD, including mutational signature 3, and an enrichment in HRD gene signature as compared to HGSOCs affecting patients at the older end of the age spectrum. Albeit not statistically significant, we did observe a numerically higher proportion of patients with a CCNE1 amplification in HGSOCs in older patients in both cohorts analyzed, and these were mutually exclusive with germline BRCA1/2 mutations. These results are consistent with the observation that CCNE1 amplification is more frequent in BRCA1/2 wild-type HGSOCs. Furthermore, CCNE1-amplified ovarian cancers have been shown to carry a worse prognosis, mainly because of platinum resistance and likely poor response to PARP inhibition.35,36

Since the discovery of BRCA1 in 1994 and BRCA2 in 1995,37 women with BRCA1/2-deficient HGSOCs have comprised a population of interest. HGSOCs affecting patients with BRCA1 or BRCA2 germline mutations have been shown to have earlier disease onset and improved survival, mainly attributed to better response to platinum-based chemotherapy.37 Such survival benefit has also been seen in HGSOCs with HRD.37 Furthermore, great strides have been made in terms of the therapeutic use of PARP inhibitors since the first pre-clinical data were released in 2005.38-40 Most of the recent trials of PARP inhibitors in the upfront treatment of ovarian cancer have demonstrated a significant improvement in PFS,7,9 leading to the Food and Drug Administration (FDA) approval of niraparib and olaparib with bevacizumab as maintenance regimens after completion of upfront platinum-based chemotherapy irrespective of the underlying genomic subtype. All studies, however, showed the most robust response to PARP inhibition in women with either a BRCA1/2 mutation or a positive HRD score, whereas the benefit in HRD-negative population was either modest with niraparib, or not apparent at all in the case of combinatorial treatment with olaparib and bevacizumab.7-10 Given the side effects of PARP inhibitors, including the risk of therapy-related leukemia,41 and the financial toxicity associated with this long-term treatment,42,43 identifying the women most likely to benefit from PARP inhibitor therapy, especially in the population that does not undergo routine HRD testing, remains of paramount importance. Our data show that HGSOC occurring in older women are less likely to be underpinned by genomics features of HRD/ BRCA1/2 alterations, show lower enrichment for an HRD gene signature, and thus are less likely to derive benefit from PARP inhibitors. Given the different frequencies of HRD genomic features according to age groups identified in this study and the hypothesis that the benefit of PARP inhibitors in the population with HGSOCs would vary according to the frequency of HRD, further studies are warranted to define whether HRD-directed therapies would constitute the optimal choice in “older” HGSOC patients.

In the MSK cohort, no germline BRCA1 or BRCA2 mutations were identified in older women, while three BRCA1 and two BRCA2 germline mutation were found in the 15 younger women. Consistent with this observation, in the larger TCGA cohort, no BRCA1 germline mutations were identified in older women, whereas eight were seen in the 38 younger women. Interestingly, the rate of BRCA2 germline mutations was the similar in younger (n=3, 8%) and older (n=4, 13%) women in the TCGA cohort. Although it is known that ovarian cancer develops approximately 10 years later in women with a BRCA2 mutation, in the 50s instead of in the 40s,44 unlike breast cancer, the age differential between our cohorts should be wide enough to account for this offset. It is possible that with a larger cohort, the difference in rate of germline BRCA1 and BRCA2 mutations would be more pronounced between younger and older women.

Several studies have linked CLOVAR survival signatures to outcomes in women with advanced-stage ovarian cancer, with the mesenchymal subtype having the worst prognosis, given its association with lower rates of complete resection during surgery and worse outcomes.45-47 The small number of younger/ older cases of the TCGA cohort studied does not allow for survival analysis, however we noted that the frequency of HGSOCs of mesenchymal subtype was similar between the age groups in our study. We further found the proliferative CLOVAR subtype more common in HGSOCs of older women, a subtype associated with a lower likelihood of BRCA1 or BRCA2 germline mutations,34 whereas HGSOCs in younger women were more frequently of immunoreactive CLOVAR subtype.

This study has several limitations. Whilst we could identify genomic features of HRD using whole-exome sequencing, whole-genome sequencing would be required to identify other types of DNA repair defects and/or types of genetic instability present in the HGSOCs lacking HRD (e.g. fold-back inversions). Furthermore, although we used the TCGA dataset to confirm findings of the MSK cohort, the number of samples in each group was limited, as we focused on keeping homogeneity within the clinical characteristics, and larger series are required to confirm our observations. Finally, the age groups in this study were defined on the basis of the age distributions in the MSK and TCGA cohorts, given the lack of a generalizable cut-off for “young” or “old” HGSOC patients. Therefore, the results of this study are only comparable to those performed in HGSOC populations with an age distribution similar to that reported in our study.

In conclusion, we demonstrate a predominance of HRD features in HGSOC occurring in younger women, and a higher prevalence of aging-related mutational signatures and fewer BRCA1 germline mutations in older HGSOC patients. These data highlight the importance of accurate HRD evaluation in all women with HGSOC, in particular those diagnosed at an older age, to appropriately allocate treatment with PARP inhibitors without undue adverse effects and financial toxicity, whilst not missing women who would benefit from targeted PARP inhibitor therapy.

HIGHLIGHTS.

  • Germline BRCA1/2 mutations are less common in older women with HGSOC

  • Genomic HRD features are more frequent in HGSOC in younger women

  • HGSOCs in older women more frequently harbor CCNE1 amplification

  • HGSOCs have a dominant HRD signature in younger and aging signature in older women

ACKNOWLEDGEMENTS

F.P. is partially funded by a National Institutes of Health/National Cancer Institute K12 CA184746 grant, J.S.R.-F. is funded in part by a Breast Cancer Research Foundation grant, BW in part by Breast Cancer Research Foundation, Cycle for Survival and Stand Up to Cancer grants. D.Z. is supported by the Ovarian Cancer Research Foundation Liz Tilberis Award, and the Department of Defense Ovarian Cancer Research Academy (OC150111). Research reported in this publication was supported in part by the Cancer Center Support Grant of the National Institutes of Health/National Cancer Institute (P30 CA008748), and by the Weickart Ovarian Cancer Postdoctoral Fellowship.

Footnotes

CONFLICTS OF INTEREST

N.R. reports research support/ grants from Pfizer, BMS and REPARE Therapeutics as well as honoraria from REPARE Therapeutics and lllumina, outside the scope of this study. D.S.C. reports membership of the medical advisory boards and stock options of Bovie Medical Co (now Apyx Medical) and Verthermia Inc, Chief Editor and Shareholder of C Surgeries, and ad hoc membership of the medical advisory board of Biom ‘Up, outside the scope of the submitted work. N.R.A.-R. reports institutional grants from GRAIL and Stryker, outside the scope of this study. D.Z. reports personal/consultancy fees from Merck, Genentech, Synlogic Therapeutics, Biomed Valley Discoveries, Trieza Therapeutics, Tesaro, and Agenus, and institutional research support from Genentech, Astra Zeneca, and Plexxikon, all outside of the scope of the submitted work. J.S.R.-F. reports receiving personal/consultancy fees and is a member of the scientific advisory board of Repare Therapeutics. J.S.R.-F. also declares receiving personal/consultancy fees from Goldman Sachs and Paige.AI, membership of the scientific advisory boards of VolitionRx and Paige.AI, membership of the Board of Directors of Grupo Oncoclinicas, and ad hoc membership of the scientific advisory boards of Roche Tissue Diagnostics, Ventana Medical Systems, Novartis, Genentech and InVicro, all outside the scope of this study. B.W. reports membership of the ad hoc scientific advisory board of REPARE Therapeutics, outside the scope of the submitted work. The remaining authors have no conflicts of interest to declare.

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