Breast cancer associated pathogenic variants among women 61 years and older with triple negative breast cancer

Abstract

Women with triple negative breast cancer (TNBC) have a high prevalence of BRCA1 mutations, and current clinical guidelines recommend genetic testing for patients with TNBC aged ≤60 years. However, studies supporting this recommendation have included few older women with TNBC.

Methods:

Genetic testing results from women aged >60 years with TNBC enrolled in the Clinical Cancer Genomics Community Research Network (CCGCRN) registry were included in this analysis. Prevalence of breast cancer-associated pathogenic variants (PVs) was compared across age groups.

Results:

We identified 151 women with TNBC aged >60 years (median 65 years; SD 5.3). Of these, 130 (86%) underwent genetic testing, and a breast cancer--associated PV was identified in 16 (12.3%; 95% CI 7–19): BRCA1 (n = 6), BRCA2 (n=5), PALB2 (n = 2), ATM (n = 1) and RAD51C (n=2). We found no differences in the proportion of patients with close blood relatives with breast (≤50 years) or ovarian cancer (any age) between PV carriers (37.5%) and non-carriers (34.2%) (p=0.79). Among PVś carriers, the proportion of older women with a BRCA1 PV was lower when compared to younger women (37.5% vs 77.2%; p<0.01).

Conclusion:

Breast cancer-associated PVs were found in an important proportion of women aged >60 years with TNBC undergoing genetic testing, including greater representation of BRCA2. These results suggest that older women with TNBC should be offered genetic testing, and that their exclusion based on chronologic age alone may not be appropriate.

Introduction

Breast cancer (BC) is the most common malignancy among women aged ≥65 years worldwide. In 2018, 591,791 new BC cases were diagnosed and 225, 662 deaths were reported in this age group, representing the second cause of cancer-related deaths after lung cancer. As the population ages, the number of patients with BC is also expected to increase by about 70% over the next twenty years ¹. Older women most commonly present with hormone receptor positive breast cancer. However, a substantial proportion are diagnosed with triple negative breast cancer (TNBC) (estrogen receptor negative, progesterone receptor negative and HER2 negative), which is associated with a more aggressive behavior ². TNBC is often caused by BC-associated germline mutations ^3,4, and its presence is recognized as a criterion for genetic cancer risk assessment (GCRA) according to international guidelines. However, those same guidelines recommend that only women aged 60 years or younger should be considered as candidates for genetic testing and GCRA⁵.

The prevalence of pathogenic variants (PVs) in BC susceptibility genes varies depending on risk factors such as age at diagnosis, family history of breast and ovarian cancer, and BC subtype. While older age is usually considered as an exclusion criteria for genetic testing, some recent publications suggest that the prevalence of BC-associated PVs among older women with BC is larger than previously thought ⁶.

We aimed to characterize the germline mutation profile of women with TNBC aged >60 years at the time of BC diagnosis in the Clinical Cancer Genomics Community Research Network (CCGCRN), a large consortium of collaborating clinics across the United States and Latin America.

Materials and Methods

Women aged 61 years or older at the time of TNBC diagnosis who were enrolled in the CCGCRN between 1997 and 2020 were included in this analysis. The CCGCRN is a large research group of over 40 collaborating sites in the United States and Latin America that serves as a biospecimen repository that includes personal and family medical history. TNBC was defined by the lack of expression of estrogen receptors (< 1% of cells with nuclear positivity), progesterone receptors (<1% of cells with nuclear positivity), and human epidermal growth factor receptor 2 (HER2) by immunohistochemistry (0 or 1+), or lack of amplification by in situ hybridization in the case of HER2. All women received GCRA at cancer centers and community-based clinics from sites in the United States and Latin America. Genetic testing was performed utilizing various methods and depended on availability of specific gene tests in that era and each institution’s practice. Informed consent was obtained from all participants, and the institutional ethics review boards at each institution approved the study protocol.

Sociodemographic characteristics, clinical variables, multigenerational pedigrees, and genetic testing results were obtained from the CCGCRN database. Pathogenic and suspected PVs in genes known to be associated with increased BC risk were tailed according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology standards; and variants of uncertain significance (VUS) were also recorded. The observed prevalence of specific BC-associated PVs among older patients with TNBC was compared to that of the entire CCGCRN TNBC cohort, without age stratification.

Data are presented as medians, means, or proportions, and 95% confidence interval (CI) was calculated. Comparisons between women with and without PVs were performed using Fisher’s Exact Test. A two-sided p-value of <0.05 was considered as statistically significant.

Results

From January 1997 to June 2020, a total of 1610 women with TNBC were identified in the CCGCRN registry database, of which 151 were aged >60 years (median 65 y; range 61–87) at the time of BC diagnosis and 19.2% (95%CI 12.8–27) were ≥ 70y. One-hundred and thirty (86%) participants underwent genetic testing, including multigene panel testing in 82 (63.0%) and BRCA testing in 48 (36.9%) women. Forty-eight (36.9%) patients reported a first or second-degree relative with breast or ovarian cancer. (Table 1)

Table 1.

Clinico-demographic characteristics

	N = 130 (%)	95% CI
Median age at TNBC (range)	65 (61–87)
≥70 years	25 (19.2)	(12.8–27)
Second BC	12 (9.2)	(4.8–15.5)
Family history of cancer	48 (36.9)	(28.6–45.8)
FDR breast cancer	17 (13.0)	(7.8–20.1)
SDR breast cancer	20 (15.3)	(9.6–22.7)
FDR/SDR ovarian cancer	20 (15.3)	(9.6–22.7)

BC: breast cancer; CI: confidence interval; FDR: first degree relative; SDR: second degree relative; TNBC: triple negative breast cancer.

A BC-associated PV was identified in 16 (12.3%; 95% CI 7–19) older women, while 22 (16.9%; 95% CI 10.4–23.3) had a VUS. Among women 61–69 y 11.4% (95% CI 6–19.1) carried a PV, while in women ≥70 y 16% (95% CI 4–36) were carriers. BC-associated PVs were identified in the following genes: BRCA1 (n = 6), BRCA2 (n = 5), PALB2 (n = 2), ATM (n = 1) and RAD51C (n = 2). The characteristics of patients with TNBC harboring PVs are shown in Table 2. We found no differences in the proportion of patients with close blood relatives with breast (≤50 years) or ovarian cancer (any age) between PV carriers (37.5%) and non-carriers (34.2%) (p = 0.79). Among 1374 women aged ≤60 y, 373 (27.1%; 95% CI 24.8–29.5) carried a PV. Frequency of specific gene PVś were included in Table 3. Older women (aged >60 years) harboring BC-associated PVs had a significantly lower proportion of BRCA1 PVs compared to younger women (37.5% vs 77.2%; p< 0.01). In contrast, the proportion of BRCA2 PVs (31.2% vs 15.5%; p = 0.09) and of non-BRCA PVs (31.2% vs 7.2%; p<0.01) was higher among older women.

Table 2.

Breast cancer associated PVs and patients’ characteristics

Gene	Nucleotide change	Age at diagnosis	Family history
ATM	c.1402_1403delAA	63	None
BRCA1	c.2463G>T	65	2 FDR w/OC
BRCA1	c.5123C>A	68	FDR and SDR w/OC
BRCA1	c.3756_3759del	74	None
BRCA1	c.68_69delAG	67	None
BRCA1	exon16-17del	78	2 SDR w/ BC
BRCA1	c.2498T>A	61	SDR w/ BC
BRCA2	c.5073dupA	63	FDR w/OC
BRCA2	c.3058A>T	65	None
BRCA2	c.6352C>T	61	None
BRCA2	c.5946delT	73	None
BRCA2	c.8837T>T	68	None
PALB2	c.509_510delGA	67	None
PALB2	c.3113G>A	66	SDR w/OC
RAD51C	c.709C>T	66	None
RAD51C	c.404+2T>C	70	None

FDR: first degree relative; SDR: second degree relative; BC: Breast cancer; OC: ovarian cancer.

Table 3.

Comparison of BC-associated PVs prevalence among older and younger women with TNBC

Gene	Total n= 389 (%)	≤60 y n=373 (%)	>60 y n = 16 (%)	P (≤ 60 vs > 60 y)
BRCA1	294 (75.5)	288 (77.2)	6 (37.5)	< 0.01
BRCA2	63 (16.1)	58 (15.5)	5 (31.2)	0.09
Non-BRCA:	32 (8.2)	27 (7.2)	5 (31.2)	< 0.01
ATM	1 (0.2)	0	1 (6.25)
BARD1	2 (0.5)	2 (0.5)	0
BRIP1	2 (0.5)	2 (0.5)	0
CHEK2	3 (0.7)	3 (0.8)	0
PALB2	13 (3.3)	11 (2.9)	2 (12.5)
PTEN	1 (0.2)	1 (0.2)	0
RAD50	1 (0.2)	1 (0.2)	0
RAD51C	4 (1.0)	3 (0.8)	2 (12.5)
RAD51D	3 (0.7)	3 (0.8)	0
TP53	1 (0.2)	1 (0.2)	0

Discussion

In this study, we report the frequency of PVs in BC susceptibility genes among women aged >60 years with TNBC. Overall, 12.3% (95% CI 7–19) of older women with TNBC carried a BC-associated germline PV, most of which were located in BRCA genes.

The frequency found in our series is similar to previous studies reporting the prevalence of PVs in TNBC (9.4–18.2%) ⁷. One clinical laboratory cohort, for example, reported a frequency of 12% in a large number of patients with TNBC of all age groups, while a multicenter study reported a prevalence of 14.6% ⁴. However, in contrast with our study, in which the median age at diagnosis was 65 years, most series included patients with a median age at diagnosis of around 50 years. The finding of a similar prevalence of PVs among an older population shows that older women with TNBC are also at risk of carrying germline PVs. BRCA1 and BRCA2 were the most frequent BC-associated PVs in our study, although the relative proportion was shifted toward BRCA2 among older patients. Interestingly, although BRCA2 PVs are known to cause later onset disease, they have traditionally been associated with hormone receptor positive disease rather than TNBC. In addition, previous reports have described that the occurrence of TNBC among BRCA1 carriers ⁸ decreases with age. Our results suggest that BRCA2 may play a role in the development of TNBC at older ages and warrants further investigation.

In addition to BRCA mutations, we also found other PVs among older women; including PALB2, RAD51C and ATM. Previous studies have reported a frequency of non-BRCA mutations among patients with TNBC of 4%, which is consistent with our results (3.8% PVs in non-BRCA genes). However, we found a higher proportion of non-BRCA PVs among older women, which might be explained by a decrease in the frequency of BRCA1 PVs. Although PALB2 and RAD51C are less well characterized as TNBC-associated genes, both have been found to be enriched among women with this disease ⁹. On the other hand, ATM is commonly found in other BC subtypes, and we have previously described ATM PVs in 3% of women 65 years and older with BC.

The proportion of older women with TNBC that has been included in genetic studies is small, and the range of reported PVs is wide (5.4 to 11.4%) depending on the selection criteria used for genetic testing ⁷, and on the number of genes studied. Couch et al. found that, among women aged ≥60 years, the risk of harboring a PV ranged from 4.7% among those without a family history of breast or ovarian cancer to 14.3% for those with a family history of ovarian cancer ⁴. On the other hand, a study that selected women with TNBC who reported not to have any relatives with breast or ovarian cancer found a mutation frequency of 6.9% in BRCA genes among women aged >60 years at the time of diagnosis³.

Although NCCN guidelines recommend testing all patients with TNBC aged ≤60 years our results, as well as other reports, have consistently shown that older women with TNBC are at higher risk of carrying PVs, and that clinicians should consider them as candidates for GCRA and genetic testing. Moreover, older women who carry PVs might be candidates for risk reducing strategies, as well as cascade testing in family members, who might also benefit from preventive strategies. Additionally, finding PVs in women with BC might guide therapy selection, such as the integration of platinum-based chemotherapy or poly ADP ribose polymerase (PARP) inhibitors.

Our study has some limitations that should be considered when interpreting our results including the sample size of older women and wide confidence intervals. In addition, only 82 older patients had multigene panel testing. However, this would only cause an underestimation of the burden of non-BRCA PVs among participants.

Overall, this study found a 12% prevalence of PVs in BC-associated genes among women with TNBC aged 60 years and older, with a high proportion of BRCA2 PVs. We believe our results support a change in clinical recommendations and in clinical practice, such that all women with TNBC should receive genetic testing regardless of their chronological age.