Effect of germline mutations in homologous recombination repair genes on overall survival of patients with pancreatic adenocarcinoma

Abstract

Purpose:

To compare the clinical characteristics and overall survival (OS) of germline mutation carriers in homologous recombination repair (HRR) genes and non-carriers with pancreatic ductal adenocarcinoma (PDAC).

Methods:

Germline DNA from 3,078 patients with PDAC enrolled in a prospective registry at Mayo Clinic between 2000 and 2017 was analyzed for mutations in 37 cancer predisposition genes. Characteristics and OS of patients with mutations in 8 genes (ATM, BARD1, BRCA1, BRCA2, BRIP1, PALB2, RAD51C, and RAD51D) involved in HRR were compared to patients testing negative for mutations in all 37 genes.

Results

The 175 HRR mutation carriers and 2,730 non-carriers in the study had a median duration of follow-up of 9.9 years. HRR mutation carriers were younger (Median age at diagnosis: 63 vs. 66 years, p<0.001) and more likely to have metastatic disease at diagnosis (46% vs. 36%, p=0.004). In a multivariable model adjusting for sex, age at diagnosis, and tumor staging, patients with germline HRR mutations had a significantly longer OS compared to non-carriers (HR: 0.83, 95% CI: 0.70 to 0.97, p= 0.02). Further gene-level analysis demonstrated that germline ATM mutation carriers had longer OS compared to patients without germline mutations in any of the 37 HRR genes (HR: 0.72, 95% CI: 0.55 – 0.94, p=0.01).

Conclusions

This study demonstrates that germline mutation carrier status in PDAC is associated with longer OS compared to non-carriers. Further research into tumor biology and response to platinum-based chemotherapy in germline mutation carriers with PDAC are needed to better understand the association with longer OS.

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy with a five-year survival of less than 10% (1, 2). There is an ongoing effort to improve the overall survival of PDAC by identifying potentially targetable somatic or germline mutations. In recent years, it has been demonstrated that germline mutations in several cancer predisposition genes may confer an increased risk of PDAC, and are detected in approximately 5–15% of patients with PDAC (3–6). Some studies have also demonstrated that the biological characteristics of PDAC tumors in germline mutation carriers of homologous recombination repair (HRR) are different from sporadic PDACs (7, 8). In addition, germline mutations in HRR genes are known to confer higher sensitivity to DNA-damaging agents and/or ionizing radiation (4, 9–11). Furthermore, a new oral class of therapeutic agents called poly-adenosine diphosphate-ribose polymerase (PARP) inhibitors has been developed to take advantage of impaired HRR in tumor cells to induce synthetic lethality. Recently, maintenance therapy with a PARP inhibitor was shown to improve progression free survival in patients with germline BRCA1 or BRCA2 (BRCA1/2 hereafter) mutations and metastatic PDAC compared to placebo (12).

Despite the improved understanding of differences in tumor biology and response to therapy in mutation carriers of HRR genes, the impact of mutation status on overall survival (OS) is still unclear. Prior studies on the impact of germline mutations on OS in PDAC had demonstrated mixed results, but these were mostly restricted to BRCA1/2 mutations and were limited by small sample sizes (13–16). Since several genes involved in HRR have similar biological functions, the differences in tumor biology and response to therapy may not be limited to BRCA1/2 mutation carriers. In this context, we evaluated the clinical characteristics of PDAC in germline mutation carriers of HRR genes and implications of these mutations on OS in large prospective hospital-based cohort of patients with PDAC.

Materials and Methods

Patient selection and Follow-up:

The study sample was derived from the Mayo Clinic Biospecimen Resource for Pancreas Research, a prospective registry offering participation to patients evaluated at Mayo Clinic Rochester for initial diagnosis of pancreatic cancer. Patients enrolled in this registry between October 12, 2000 and October 6, 2017 with PDAC were included. Patients who were enrolled in the registry more than 3 months after their initial diagnosis and those who had no further follow-up after their diagnosis were excluded. While the results of germline sequencing have previously been reported (3), the present analysis focused on OS and included 454 additional cases enrolled after the prior publication. This study was approved by the Institutional Review Board (IRB) at Mayo Clinic, and all aspects of the study were in accordance with the Declaration of Helsinki. . All patients signed written, informed consent.

Patients consenting to the study completed a baseline questionnaire on personal and family history and provided a blood sample. In addition, patient demographics, tumor characteristics, family history, and clinical outcomes were abstracted from electronic medical records to verify existing information reported by patients. For patients who did not follow up at Mayo Clinic, medical records from local institutions were requested at 1 year post diagnosis, 3 years post diagnosis and at death. A medical oncologist or trained nurse abstractor reviewed each record for abstraction of information pertaining to any treatment the patient received. Furthermore, additional follow up questionnaires were sent to patients to obtain information on treatment and outcomes while participating in the study. The abstraction of information on treatment was complete on approximately two-thirds (64.4%) of the study participants at the time of last follow up or death. For the purpose of this study, patients treated with cisplatin, oxaliplatin or carboplatin at any point during the course of treatment were considered to have received platinum-based chemotherapy.

Germline sequencing and Bioinformatics Analysis:

Germline DNA extracted from peripheral blood mononuclear cells was analyzed for germline pathogenic variants in the coding regions and consensus splice sites of 37 genes (Supplemental information and Supplemental Table 1) using a custom amplicon-based QIAseq panel (QIAGEN, Hilden, Germany). Pooled sample libraries from 768 samples were subjected to paired-end 150-base pair sequencing in each lane of a HiSeq4000 (Illumina, San Diego, CA) with a median coverage of 200X. Reads were trimmed with Cutadapt version 1.10(17) and aligned with BWA-MEM (18). Sequence realignment, recalibration, haplotype calling, and depth of coverage were conducted using Genome Analysis Toolkit (GATK) version 3.4–46 (19). Large genomic rearrangements were detected with Pattern CNV v1.1.3 (20). Annotation of mutations was provided through the BioR toolkit(21) leveraging dbNSFP v3.0(22), ClinVar (23), Clinical Annotation of Variants (24), and population frequencies from Genome Aggregation Database (gnomAD) (11) and Exome Aggregation Consortium (ExAC) (25). Pathogenic mutations were viewed with VCF-Miner (26). A 5-tier system was used to classify mutations based on the American College of Medical Genetics and the Association for Molecular Pathology guidelines (27). Pathogenic and likely pathogenic variants were analyzed together as pathogenic variants.

Statistical Analysis:

Patients with a germline mutation in one of the eight genes (ATM, BARD1, BRCA1, BRCA2, BRIP1, PALB2, RAD51C, and RAD51D) involved in HRR were considered as carriers whereas those who tested negative for germline mutation in all 37 genes were considered non-carriers. These 8 genes were selected based on prior studies demonstrating association with homologous recombination deficiency (28). Since other genes in the QIAseq panel may be associated with HRR, mutation carriers in genes other than the 8 HRR genes were excluded from primary analysis to mitigate their effect. Baseline characteristics between carriers and non-carriers were compared using Fisher’s exact test for categorical variables and ANOVA for continuous variables. OS between carriers and non-carriers was compared in a multivariable cox-proportional hazard regression model including age, sex, and stage at diagnosis as covariates along with subset analysis by specific chemotherapy regimens, year of diagnosis, and specific gene mutations. Separate sensitivity analyses for differences in baseline characteristics and OS were performed in patients with germline mutations in the 8 HRR genes (carriers) and in those who tested negative for mutations in the 8 HRR genes (non-carriers). All statistical tests were performed using SAS 9.4 statistical software (SAS Institute, Cary, NC).

Results

Out of the 3,078 patients included in the final analysis, 175 (5.7%) were found to carry a mutation in one of the 8 HRR genes: 67 (2.2%) in BRCA2, 65 (2.1%) in ATM, 20 (0.6%) in BRCA1, 12 (0.4%) in PALB2, 4 (0.1%) in BRIP1, 4 (0.1%) in RAD51C, 2 (0.1%) in BARD1, and 1 (0.03%) in RAD51D (Table 1). The non-carriers included 2730 (88.7%) patients without mutations in any of the 37 genes evaluated. The median age at diagnosis of the cohort was 65.8 years with a median duration of follow-up of 9.9 years.

Table 1:

Frequencies of germline mutations in the cohort

Gene	Number of mutation carriers (N=3078)	Percent
APC	2	0.1%
ATM	65	2.1%
BARD1	2	0.1%
BLM	9	0.3%
BRCA1	20	0.6%
BRCA2	67	2.2%
BRIP1	4	0.1%
CDKN2A	10	0.3%
CHEK2	22	0.7%
EPCAM	1	0.0%
ERCC2	13	0.4%
ERCC3	7	0.2%
FANCC	8	0.3%
FANCM	8	0.3%
KRAS	1	0.0%
MLH1	6	0.2%
MRE11A	2	0.1%
MSH2	1	0.0%
MSH6	9	0.3%
MUTYH	6	0.2%
NBN	4	0.1%
NF1	2	0.1%
PALB2	12	0.4%
PMS2	10	0.3%
PPM1D	23	0.7%
PRSS1	5	0.2%
RAD50	6	0.2%
RAD51C	4	0.1%
RAD51D	1	0.0%
RECQL	8	0.3%
RINT1	5	0.2%
SLX4	5	0.2%
TP53	6	0.2%
XRCC2	3	0.1%

Baseline Characteristics of Mutation Carriers and Non-Carriers:

Baseline characteristics of 175 mutation carriers in 8 HRR genes and 2,730 non-carriers are presented in Table 2. Mutation carriers were diagnosed with PDAC at a younger age (62.8 vs. 65.8 years, p<0.001) and were more likely to present with metastatic disease at diagnosis (46.2% vs. 35.6%, p<0.001) compared to non-carriers (Table 2). In addition, a higher proportion of mutation carriers had PDAC in the body or tail of the pancreas compared to non-carriers. Among patients with resectable PDAC, the rate of surgery was similar between the two groups. Furthermore, there were no statistically significant differences in the rates of chemotherapy between mutation carriers and non-carriers. The demographic and tumor characteristics of ATM carriers, which is one of the largest group of mutation carriers in this cohort is presented in supplemental table 2.

Table 2:

Baseline and clinical characteristics of mutation carriers of 8 HRR genes and non-carriers

	Carrier (N=175)	Non-Carrier (N=2730)	P-value
Mean age at Diagnosis (SD)	62.78 (10.69)	65.82 (10.70)	<0.001
Gender:			0.34
Male	106 (60.6%)	1553 (56.9%)
Female	69 (39.4%)	1177 (43.1%)
Ethnicity:			0.87
Non-Hispanic White	165 (95.9%)	2616 (96.2%)
Other	7 (4.1%)	104 (3.8%)
Missing	3	10
Mean BMI (SD)	28.74 (5.58)	28.59 (5.69)	0.51
Patient reported diabetes:			0.63
Yes	42 (24.0%)	700 (25.6%)
No	133 (76.0%)	2030 (74.4%)
Ever Smoker:			0.66
Yes	91 (55.2%)	1493 (56.9%)
No	74 (44.8%)	1132 (43.1%)
Missing	10	105
Mean pack years in ever smokers (SD)	26.00 (20.64)	28.18 (25.33)	0.82
Site of Pancreas Mass:			0.002
Head and adjacent parts	94 (55.6%)	1789 (67.2%)
Body/Tail	75 (44.4%)	872 (32.8%)
Missing	6	69
Pancreas cancer stage grouping:			0.004
Resectable	46 (26.6%)	692 (25.4%)
Locally Advanced	47 (27.2%)	1059 (38.9%)
Metastatic	80 (46.2%)	969 (35.6%)
Missing	2	10
Pancreas cancer surgery:			0.62
Pancreatico-duodenectomy	41 (71.9%)	611 (73.5%)
Distal pancreatectomy	15 (26.3%)	188 (22.6%)
Total pancreatectomy	1 (1.8%)	32 (3.9%)
No-surgery or missing	118	1899
Chemotherapy:			0.56
Yes	119 (83.8%)	1590 (81.9%)
No Chemotherapy	23 (16.2%)	352 (18.1%)
Missing	33	788
Radiation:			0.03
Yes	64 (50.0%)	769 (40.0%)
No radiation	64 (50.0%)	1152 (60.0%)
Missing	47	809

BMI: Body Mass Index; SD: Standard Deviation

Overall Survival:

The median OS for mutation carriers was 14.6 months (95% CI: 13.2 – 16.1 months) compared to 11.7 months (95% CI: 11.2 – 12.4 months) for non-carriers (Figure 1). In univariate analysis, the difference in the OS between mutation carriers and non-carriers did not reach statistical significance (HR: 0.86, 95% CI: 0.73 – 1.01, p= 0.07). However, in multivariable analysis adjusting for age, sex, and stage at diagnosis, mutation carrier status was associated with a significantly longer OS compared to non-carriers (HR: 0.83, 95% CI: 0.70 – 0.97, p= 0.02) (Table 3). Among surgically resectable patients, the median OS was 23.7 months in mutation carriers and 23.5 months in non-carriers (Supplemental Figure 1) whereas among non-resectable/metastatic patients, the median OS was 11.5 months in mutation carriers and 9.6 months in non-carriers (Supplemental Figure 2).

Figure 1:

Kaplan-Meier curves for overall survival in homologous recombination repair gene mutation carriers and non-carriers

Table 3:

Multivariable analysis for overall survival comparing the 8 HRR gene mutation carriers to non-carriers^#.

	Number of Events/Total	Median Survival in months (95% CI)	Multivariable Analysis
			Hazard Ratio (95% CI)	P-value
Overall:				0.02
Non-Carrier	2441/2730	11.7 (11.2–12.4)	Reference
Carrier	154/175	14.6 (13.2–16.1)	0.83 (0.70–0.97)
Subset Analysis:
Non-resectable or metastatic				0.02
Non-Carrier	1839/2028	9.6 (9.1 – 10.2)	Reference
Carrier	118/127	8.0 (5.8–12.2)	0.81 (0.67 – 0.97)
Surgically resected				0.49
Non-Carrier	565/692	23.5 (21.7 – 25.2)	Reference
Carrier	34/46	23.7 (18.4 – 45.8)	0.89 (0.63 – 1.25)
Diagnosed prior to May 2011				0.22
Non-Carrier	1650/1741	10.4 (9.7–11.0)	Reference
Carrier	105/114	13.8 (10.6–16.1)	0.89 (0.73–1.08)
Diagnosed May 2011 or later				0.04
Non-Carrier	791/989	13.7 (13.1–14.3)	Reference
Carrier	49/61	15.7 (12.4–20.5)	0.75 (0.56–1.00)
Received platinum-based chemotherapy				0.18
Non-Carrier	597/700	16.3 (15.6–17.2)	Reference
Carrier	54/61	17.8 (16.0–22.1)	0.83 (0.63–1.10)
Did not receive platinum-based chemotherapy				0.20
Non-Carrier	1838/2022	9.7 (9.1 – 10.2)	Reference
Carrier	98/112	11.5 (8.3 – 14.0)	0.88 (0.72 – 1.08)
Diagnosed prior to May 2011 and did not receive platinum-based chemotherapy				0.34
Non-Carrier	1402/1485	9.3 (8.6 – 9.9)	Reference
Carrier	81/89	10.1 (8.0 – 14.0)	0.90 (0.72 – 1.13)
Diagnosed prior to May 2011 and received platinum-based chemotherapy				0.43
Non-Carrier	243/249	15.6 (14.5–17.4)	Reference
Carrier	22/23	17.8 (15.0–45.8)	0.84 (0.54–1.31)
Diagnosed May 2011 or later & received platinum-based chemotherapy				0.24
Non-Carrier	354/451	16.7 (15.9–17.5)	Reference
Carrier	32/38	19.7 (15.4–22.3)	0.81 (0.56–1.17)
Diagnosed May 2011 or later and received FOLFIRINOX				0.43
Non-Carrier	246/322	17.4 (16.6–20.0)	Reference
Carrier	28/32	17.7 (12.4–28.5)	0.85 (0.57–1.27)
Diagnosed May 2011 or later and received irinotecan				0.41
Non-Carrier	291/382	17.3 (16.6–19.3)	Reference
Carrier	30/35	17.7 (12.4–25.0)	0.85 (0.58–1.25)
Non-resectable/metastatic and received platinum-based chemotherapy				0.12
Non-Carrier	490/591	15.4 (14.1 – 16.6)	Reference
Carrier	42/47	17.5 (14.6 – 21.8)	0.78 (0.57 – 1.07)
Surgically resected and received platinum-based chemotherapy				0.86
Non-Carrier	106/107	22.9 (20.1 – 27.1)	Reference
Carrier	12/14	23.7 (17.7 – NE)	1.06 (0.57 – 1.95)
Subset analysis by mutation carrier status in each gene€
Non-carriers	2441/2730	11.7 (11.2–12.4)	Reference
ATM carriers	57/65	15.7 (14.4–21.1)	0.72 (0.55–0.94)	0.01
BRCA1 carriers	19/20	9.2 (5.8–16.1)	1.26 (0.80–1.98)	0.34
BRCA2 carriers	58/67	15.0 (11.5–20.0)	0.81 (0.62–1.05)	0.10
PALB2 carriers	10/12	14.2 (12.4–66.9)	0.74 (0.40–1.38)	0.33
Subset analysis by receipt of platinum-based chemotherapy among mutation carriers
Did not receive platinum-based chemotherapy	76/80	7.7 (5.8 – 10.1)	Reference
Received platinum-based chemotherapy	42/47	17.5 (14.6 – 21.8)	0.46 (0.30 – 0.68)	<0.001

CI: Confidence Interval; FOLFIRINOX: Regimen consisting of fluorouracil, leucovorin, irinotecan and oxaliplatin;

^#: Analyses were adjusted for age at diagnosis, sex, and stage at diagnosis (where appropriate);

^€: Survival in carriers of germline mutations in each of the 8 homologous recombination repair genes compared to non-carriers; Hazard ratios for genes with less than 5 mutation carriers not estimated.

NE not estimable

Subgroup Analyses:

Further exploratory analyses were performed by stage of diagnosis, year of diagnosis, and type of chemotherapy (Table 3). Among patients with metastatic or non-resectable PDAC, mutation carriers were observed to have a significantly longer OS compared to non-carriers (HR: 0.81, 95%CI: 0.67 – 0.97, p=0.02). In addition, mutation carrier status was also significantly associated with longer OS among patients diagnosed after May 2011 (when FOLFIRINOX use started) compared to non-carriers diagnosed during the same time period (HR: 0.75, 95% CI: 0.56 – 1.00, p=0.04). However, specific chemotherapy regimens including platinum agents and FOLFIRINOX were not associated with OS. Similarly, on separate analysis of metastatic/non-resectable and surgically-resectable PDAC cases receiving platinum-based chemotherapy, mutation carriers were not noted have a statistically significant difference in OS compared to non-carriers (Table 3). Furthermore, no difference in OS by mutation carrier status was noted among patients not receiving platinum-based chemotherapy. However, restricting the analysis to mutation carriers with metastatic or non-resectable disease, patients who received platinum-based chemotherapy had better OS compared to mutation carriers who did not receive platinum based chemotherapy (HR:0.46, 95%CI:0.30 – 0.68, p<0.001) (Supplemental Figure 3).

Further gene-level analysis demonstrated that germline ATM mutation carriers had longer OS compared to patients without germline mutations in any of the 37 HRR genes (HR: 0.72, 95% CI: 0.55 – 0.94, p=0.01). Significant differences in OS were not noted for BRCA1, BRCA2, or PALB2 carriers compared to non-carriers (Table 3 and Supplemental Figures 4–5).

Sensitivity Analysis:

In sensitivity analysis including 175 mutation carriers in 8 HRR genes compared to the remaining 2,903 patients negative only for a mutation in these 8 genes, the overall differences in baseline characteristics and OS were similar to the primary analysis (Supplemental Tables 3 and 4).

Discussion

In a large prospective registry of patients with PDAC, we observed an association between germline HRR mutations and improved OS. Prior studies primarily focused on OS in PDAC with BRCA1/2 mutations and exposure to platinum based chemotherapy (13, 14, 29–33). These studies have demonstrated mixed results, with some studies demonstrating longer OS (29, 33) while others demonstrated shorter or similar OS (13, 14). Fewer studies have evaluated the role of other DNA-damage repair or HRR genes (15, 33–36). However, the majority of the prior studies were limited by their retrospective nature and small sample. In contrast, the present study is the largest to date, to the best of our knowledge, for carriers of HRR genes in patients with PDAC. In addition, the present study included a large number of non-carriers. Furthermore, the prospective collection of clinical outcomes is a significant strength of this study. The findings of our study have significant implications for future research, primarily in understanding the differences in tumor biology and response to standard treatments in germline mutation carriers with PDAC. In addition, these findings will aid in appropriate counseling of prognosis in mutation carriers with PDAC.

The difference in OS observed in this study could be due to differences in tumor biology and/or responses to standard treatments in germline mutation carriers with PDAC. Differences in OS due to unique tumor biology would be suggestive of prognostic nature of HRR mutations while OS difference due to response to therapy, e.g. platinum-based chemotherapy, would point towards predictive nature of HRR alterations. The prognostic versus predictive nature of HRR defect deserves special attention. Molecular studies involving sporadic PDAC have identified a complex mutational landscape with a high frequency of somatic mutations in KRAS, TP53, SMAD4, CDKN2A, and in genes involved in cell cycle regulation, TGF-β signaling, HRR, chromatin regulation, and axonal guidance pathways (7, 8, 37–39). It is not entirely clear if germline mutation associated PDACs have similar landscapes of somatic mutations and mutational signatures as sporadic PDAC, but differences in tumor biology have been reported from smaller series. For example, significant enrichment for germline mutations in HRR genes in KRAS wild-type PDAC (8) and among patients with the mutational signature associated with high genomic instability (7) have been observed. While this study did not evaluate somatic mutations in PDAC, it does establish a foundation for future studies to evaluate if differences in tumor biology may explain the association with improved survival observed in this study.

Prior studies have demonstrated increased responsiveness to radiation and chemotherapy, particularly platinum-based chemotherapies, in PDAC associated with germline mutations (9, 14, 36, 40, 41). In addition, among patients with advanced PDAC treated with platinum based chemotherapy, OS has been shown to be longer for patients with HRR defect (33, 42, 43), which is suggestive of a predictive effect of HRR mutation on OS with platinum-based chemotherapy. While we observed that mutation carriers with advanced (non-resectable or metastatic) PDAC who received platinum-based chemotherapy had better OS compared to mutation carriers who did not (Supplemental Figure 1), we did not observe an association between OS and mutation carrier status among patients receiving platinum-based chemotherapy (Table 3). These findings highlight the importance of platinum-based chemotherapies in mutation carriers but do not confirm the predictive effect of HRR mutations on OS with platinum-based chemotherapy. Similarly, the association with improved OS in mutation carriers after platinum based therapy became standard of care in May 2011and in non-resectable/metastatic cases (in whom platinum-based chemotherapy is more likely to be administered) suggest, but do not confirm, that HRR defect may be predictive of differential response to platinum-based therapies. In contrast, the observation of no significant difference in OS between mutation carriers and non-carriers with specific chemotherapy regimens such as FOLFIRINOX argues against predictive effect of platinum-based chemotherapy. However, the lack of predictive effect of HRR mutation on OS with platinum-based chemotherapy in this study may be due to smaller numbers of patients in the analyzed subsets, and does not rule out this possibility.

Ultimately, this study is not adequately powered to delineate whether the improvement in OS in germline mutation carriers is due to higher response to chemotherapy or inherent differences in tumor biology or a combination of both. However, similar to other studies (41–43), this study suggests that platinum-based therapies are important in treatment of mutation carriers with advanced PDAC. The current National Comprehensive Cancer Network guidelines on PDAC supports the use of cisplatin in BRCA1/2 mutation carriers, but the use of these agents in PDAC associated with other HRR genes has not been well-studied. Our study suggests that the sensitizing effects of platinum agents may extend beyond BRCA1/2 to other HRR genes. Larger randomized studies are needed to identify if mutation carriers in HRR genes other than BRCA1/2demonstrate significant responseto particular chemotherapy regimens. Biomarkers predictive of differential therapeutic response are also urgently needed. In addition, with the availability of PARP inhibitors, future clinical trials could include rational combinations of PARP-inhibitors with chemotherapeutic agents, immunotherapy and/or radiation therapy to leverage the germline mutation status to further improve OS (10).

The present study also demonstrated significant difference in OS between ATM mutation carriers and non-carriers. This is in contrast to a prior study that demonstrated poor survival with tumoral loss of ATM by immunohistochemistry in PDAC (44). The biological characteristics of PDAC tumors associated with germline ATM carriers are understudied. In a small study of 24 breast cancer tumors from germline ATM carriers, none of the tumors displayed high activity of mutational signature 3 associated with HRR defect (45). In addition, it has been noted that germline ATM mutations and TP53 somatic mutations may be epistatic (41, 45). Somatic mutation in TP53 is known to be associated with poor prognosis in multiple malignancies including PDAC (46–48). These findings raise the possibility that germline ATM associated PDAC might be a distinct entity compared to BRCA1/2 associated PDAC or sporadic PDAC. Further evaluation of tumor biology of ATM associated PDAC tumors through DNA sequencing and RNA expression studies are needed to fully understand the unique nature of these tumors and implications on OS. In contrast, this study did note a difference in OS for BRCA1 or BRCA2. These analyses at gene-level may be underpowered to detect a difference in OS. However, further evaluation of differences in tumor biology and response to therapy between ATM, BRCA1/2 and PALB2 carriers should also be evaluated in larger studies in the future.

In addition to the survival differences, this study also showed that germline mutation carriers with PDAC are more likely to be younger and present with metastatic disease at diagnosis. Germline mutation carriers of HRR genes are diagnosed with breast and ovarian cancers at an earlier age (49) and are also more likely to have metastatic rather than localized prostate cancer compared to the general population (50). Similar associations in PDAC, although suspected, had not been observed previously and are novel findings of this study.

Limitations

Because this study was performed using a prospective registry from a single institution, it has several strengths compared with similar prior studies. However, a number of limitations exist. Since we only analyzed patients who consented to participate in the registries, a selection bias cannot be ruled out. We evaluated combined outcomes for 8 clinically relevant HRR genes, but it is possible that not all of the HRR genes may have similar biological properties. In addition, we did not take into account somatic mutations in tumors, which can independently affect outcomes as patients with somatic HRR defect are known to respond to platinum based chemotherapy and PARP inhibitors (41, 51, 52). Furthermore, the lack of ethnic/racial diversity and incomplete information on treatment is an important limitation of this study. Finally, even though we evaluated a large number of patients, the total number of germline mutation carriers was relatively small, and we may not have had power to detect differences in sub-group analyses.

Conclusions

This study demonstrates that germline mutation carriers with PDAC have a longer OS compared to non-carriers after adjusting for age, sex, and stage at diagnosis. Further research into tumor biology and therapeutic response to chemotherapy in PDAC associated with germline mutations in HRR genes are needed to identify not only prognostic but also predictive biomarkers in order to develop personalized treatment options for this unique patient population.

Translational Relevance of the study:

In this prospective study of patients with pancreatic cancer, an association between germline mutations in homologous recombination repair genes and improved overall survival was noted , possibly related to distinct tumor biology or increased response to therapy in mutation carriers.. Molecular studies involving sporadic pancreatic cancer have identified a complex mutational landscape with a high frequency of somatic mutations in KRAS, TP53, SMAD4, CDKN2A. However, it is not entirely clear if pancreatic tumors associated with germline mutations have similar landscapes of somatic mutations and mutational signatures as sporadic pancreatic cancer. In smaller studies, differences in tumor biology have been reported between sporadic pancreatic cancer and germline mutation associated pancreatic cancers. This study establishes a foundation for future studies to further investigate whether differences in tumor biology between sporadic and germline mutation associated pancreatic cancer may explain the association with improved survival observed in this study.