Impact of BRCA mutation on the survival and risk of contralateral breast cancer in Asian breast cancer patients

Breast cancer is increasing around the globe, including Asia. We aimed to examine the survival and risk of contralateral breast cancer (CBC) in Asian breast cancer patients with BRCA mutations. A total of 128 breast cancer patients with germline BRCA mutations and 4,754 control breast cancer patients were enrolled. Data on clinical–pathologic characteristics, survival, and CBC were collected from the medical record. The rates of survival and CBC were estimated by Kaplan–Meier method. The mean age of onset in BRCA mutation carriers was significantly younger than control patients (BRCA vs. Non-BRCA: 43.9 vs. 53.2 years old). BRCA mutation carriers had a higher proportion of triple-negative breast cancer (TNBC) (52%) than control patients (12%, p < 0.001). The risk of CBC was significantly higher in BRCA mutation patients than in control cases (hazard ratio (HR) = 3.95, 95% CI 2.71–5.75); when stratified by genotype, the HRs (95%CI) were 4.84 (3.00–7.82) for BRCA1 and 3.13 (1.78–5.49) for BRCA2 carriers, respectively. Moreover, BRCA1 mutation patients with triple-negative breast cancer (TNBC) as their first breast cancer had the highest risk of CBC (HR = 5.55, 95% CI 3.29–9.34). However, we did not observe any differences in relapse-free survival and overall survival between mutation carriers and control patients. Our study suggest that BRCA patients had a significantly higher risk of developing CBC, particularly for BRCA1 mutation carriers with TNBC as the first breast cancer.


Introduction
Breast cancer, the most common type of malignancy, is the leading cause of cancer-related death of women in Taiwan and worldwide [1]. One phenomenon of Asian breast cancer patients is that they have a relatively younger onset age than Western patients [2,3], which suggests that a proportion of Asian breast cancer patients is being affected by the genetic mutation of inherited genes such as BRCA1 and BRCA2 [2,3].
Women with germline BRCA mutations have extremely high lifetime risks of developing breast and ovarian cancers [4][5][6][7]. Previous studies have shown that the cumulative incidence of breast cancer for BRCA1 and BRCA2 mutation carriers by 80 years old was about 72% [confidence interval (CI) 65% -79%] and 69% (61% -77%), respectively [7]. More specifically, reports from Asian BRCA studies revealed that BRCA1 and BRCA2 mutation carriers have a 49 -54% and 35 -48% chance of developing breast cancer, respectively [6,7]. The risk of recurrent or contralateral breast cancer (CBC) also significantly increases in BRCA mutation carriers compared to non-BRCA carrier patients [4,[8][9][10]. The prognostic impact of germline BRCA mutations in breast cancer patients is controversial. A prospective study revealed similar prognoses in patients with and without BRCA mutations [11]. In contrast, another large cohort and meta-analysis studies suggested that BRCA mutations were associated with worse overall survival [12,13].
However, the majority of studies to date focused on the clinical manifestation of BRCA mutations are from European, North American, African or African-American populations. Although the number of reports from Asian populations have been increasing, most are focused on the prevalence and epidemiology of BRCA [2,3,[14][15][16][17][18]. The clinical characteristics, pathologic features, prognosis, and risk of CBC remain uncertain in Asian patients with BRCA -mutated breast cancer. To estimate the survival and risk of CBC, we used information from a total of 4,882 Taiwanese (ethnic Han Chinese) breast cancer patients. Among them, one-hundred and twenty-eight cases were carriers of germline BRCA1 or BRCA2 mutations.

Patient
We collected 128 breast cancer patients who carried germline BRCA1 or BRCA2 mutations during the period 1995 -2019 from previous academic studies and hospital-based gene diagnoses [2,3]. The criteria used to select patients for genetic studies or to recommend them for genetic diagnosis was based mainly on NCCN guidelines, which consider factors such as young-onset age, significant familial history, and whether age at TNBC diagnosis is less than 60 years old [19]. Ninety patients were diagnosed in National Taiwan University Hospital (NTUH); the remaining were diagnosed at other Taiwanese hospitals.
The control group came from NTUH breast cancer patients. In NTUH's cancer registry database, we found a total of 6,948 patients during the period 1995-2019. First, we excluded 1,470 patients who had incomprehensive data, which means that some fields, such as tumor size or lymph node status, may have been lacking. Second, we excluded patients with BRCA mutations and patients who had family history of breast cancer and/or ovarian cancer in their first/ second relatives. This strategy eliminates BRCA mutations in control patients as much as possible. A final total of 4,754 breast cancer patients were enrolled as the control patient group.
All clinical, pathologic data, and survival information were recorded from medical charts. The presence of estrogen receptors (ER), progesterone receptors (PR), and Her2 were determined by immunohistochemical staining. The presence of ER or PR was considered negative when less than 1% of the tumor cells showed positive staining. Positive expression of hormone receptors was classified as luminal type breast cancer, which can be further divided into luminal A and B classifications. We classified breast tumors with PR expression less than 20%, Ki67 more than 20%, and/or histologic grade III as Luminal B type [20,21]. For Her2 staining, a score of 0 or 1 + was considered negative; specimens with a score of 2 + were confirmed by fluorescence in situ hybridization analysis. The tumor histological grade was defined using the Nottingham combined histological grading system.

Statistics
We used the chi-squared test and Fisher's exact test to calculate the significance of variances between each group. We calculated and compared the survival by different groups using Kaplan-Meier analysis. Followup (in years) was considered as the time interval between the date of breast cancer diagnosis and the date of these endpoints: date of CBC diagnosis, date of death, latest date of follow-up, or end of followup (December 31, 2019), whichever came first. Cox proportional hazards regression analysis was used to estimate the hazards ratios of survival and second breast cancer and corresponding 95% confidence interval (CI) for various factors, including tumor size, lymph node status, molecular types, and genotype of BRCA. Statistical analyses were performed using SPSS software (version 17.0) and all p-values are two-sided, and p-values less than 0.05 are considered statistically significant.
There was no difference in the distributions of tumor size and LN status between BRCA and non-BRCA mutation patients. BRCA mutation patients had a significantly higher risk of developing second non-breast cancer (p < 0.001). The main second malignancy was ovarian cancer, whose incidence was similar between BRCA1 and BRCA2 patients. For the 17 patients with ovarian cancer, twelve (70.6%) of them developed ovarian cancer after breast cancer and 5 cases had ovarian cancer before breast cancer. The types of the second malignancy for the control cases were significantly different from that of BRCA patients; the most common cancer of the control patients was lung cancer (p < 0.001).  (Fig. 1B).
The prognostic factors for RFS in both BRCA and control patients were the tumor size and LN classification (Fig. 1C  -F). Large tumor sizes and advanced LN classification resulted in poor RFS. When stratified by molecular types, the control patients with ER( +) Her2(-) LuminalA breast cancer had the best RFS out of all other types of breast cancer. Patients with ER(-) Her2( +) breast cancer had the worst RFS (Fig. 1G). For BRCA mutation carriers, patients with TNBC had a better RFS trend than those with other types of breast cancer (Fig. 1H), probably because most TNBC patients had stage I breast cancer.

Characteristics of CBC risk in BRCA mutation carriers
Previous studies reported that patients younger than 40 years old had a higher risk of having CBC [9], so we divided patients into two groups: people at or younger than 40 years old and people older than 40 years old. However, the CBC risk was similar between BRCA patients younger and older than 40 years old (Fig. 3A). We found that there was a higher trend of CBC risk in BRCA1 mutation patients (HR = 1.814, 95% CI 0.865 -3.805, p = 0.115) compared to that of BRCA2 mutation carriers. Similarly, TNBC patients had a higher trend of developing CBC than ER( +) BRCA patients (HR = 1.657, 95% CI 0.778 -3.530, p = 0.185, Fig. 3B). When genotype and molecular types were integrated, BRCA1 patients with TNBC had the highest risk of CBC compared to other BRCA mutation patients (Fig. 3C  and D). The CBC risk of BRCA1 patients with TNBC was 39.3% (95% CI 19.9% -58.7%) and 63.6% (95% CI 39.0% -88.1%) at 10 and 15 years, respectively. In comparison to the control patients, BRCA1 patients with TNBC had a greater than five-fold risk of developing CBC (HR = 5.550, 95% CI 3.295 -9.349, p < 0.001).

Discussion
This is, to the best of our knowledge, the first study to investigate the clinical-pathologic characteristics, survival, and risk of CBC in Asian BRCA -mutated breast cancer patients. The characteristics of early onset and molecular type of breast cancer in our patients are compatible with results in Western ethnic patients [4,22]. We observed similar survival between BRCA -mutated and non-mutated breast cancer patients. However, a significantly elevated risk of CBC was noted in BRCA -mutated breast cancer patients, especially BRCA1 patients with TNBC. The risk of CBC was about four times higher in BRCA mutation carriers than noncarriers. The cumulative 10-year risk of CBC was about 26.0%. Prior studies estimated the 10-year risk of CBC to be about 21% -30%. When the observation period lengthened to 20 years, the risk of CBC could increase up to about 40% [9,23]. Many studies have investigated CBC risk factors. Graeser MK et al. and van den Broek AJ et al. reported that a younger onset age of the first breast cancer was associated with a significantly elevated risk of CBC in patients with BRCA mutations [9,24]. However, we did not find an elevated risk of CBC in BRCA patients younger than 40 years old in our present cohort, which may be due to ethnic differences or limited followup time. Additionally, the small number of youngonset patients in our cohort may be another reason why our results showed no difference in CBC risk between patients younger and older than 40 years old. In our cohort, only 39% of patients were younger than 40 years old when they had their first breast cancer; the median onset age of the first breast cancer in BRCA1 and BRCA2 patients were 42.2 and 45.6 years old, respectively. We are continuing enrolling early onset of Taiwanese breast cancer patients to better understand the epidemiology as well as risk factors of CBC in Asian breast cancer patients.
However, in concordance with previous studies [9], our data revealed that BRCA1 patients had a higher trend of developing CBC than BRCA2 patients. When classified by genotype and molecular types, BRCA1 patients with TNBC had the highest risk of getting CBC; the CBC risk of these patients was up to 63.6% (95% CI 39.0% -88.1%) at 15 years, about a five-fold increase in comparison to control patients. BRCA1 patients with ER( +) breast cancer had similar risk of developing CBC compared to whole BRCA2 patients (Fig. 3C).
The ASCO consensus and NCCN guidelines suggest that risk-reducing mastectomy and contralateral prophylactic mastectomy (CPM) should be considered for BRCA mutation carriers [19,25]. CPM can reduce the risk of CBC. Some studies even reported that CPM can reduce mortality for BRCA mutation patients in the long-term follow-up [26][27][28]. However, the CPM rate was relative lower in Asian countries [29]. In our study, only two BRCA mutation patients received CPM; this is one of the reasons of the high CBC risk in our cohort. Therefore, CPM will be considered for our patients to reduce the risk of CBC, especially for BRCA1 patients with TNBC.
The impact of germline BRCA mutations on the survival of breast cancer patients is controversial. A prospective study revealed that patients with young-onset breast cancer who carry a BRCA mutation have similar survival as noncarriers [11]. Another large cohort study showed that BRCA1 mutation carriers, independent of clinical-pathological and therapy characteristics, had a worse overall survival (OS) than noncarriers [13]. Subsequent ovarian cancer in BRCA1 breast cancer survivors may contribute to the lower OS. The breast cancer mortality rate was not significantly superior in BRCA mutation patients [13]. Our study demonstrated that BRCA breast cancer patients had a similar RFS in comparison to that of control patients. However, the risk of nonbreast second malignancies, especially ovarian cancer, was significantly higher than that of control patients. Besides from ovarian cancer, we also saw two cases of endometrial cancer. One patient's endometrial cancer received multigene sequencing and the result showed loss-of-heterozygosity of the BRCA1 gene, indicating that BRCA1 mutation was involved in tumorigenesis. Furthermore, several recent studies found an increased risk of uterine cancer in BRCA mutation carriers [30,31]. These facts suggested that the prevention of second malignancies is an important issue in BRCA breast cancer survivors.
Asians comprise 60% of the world's population and this number is still increasing; this fact suggests that significant numbers of breast cancer patients are Asian or Asianancestry women. Contrasting (United State) US population, the Asian breast cancer have a distinct age-specific incidence and clinicopathological patterns [32]. Breast cancer incidence of Asian women peaked at 45-49 years, and higher proportions of ER( +) breast cancer and lower proportions of TNBC at a younger age, whereas the highest incidence of US women was at 75-79 years, and ER( +) breast cancer increased with age [32]. Breast cancer-specific survival of Chinese women in the US is better than that of Western ethnicity [33]. However, Asian BRCA patients had a similar epidemiology, mutation spectrum, and pathology, compared to Western countries [15]. For example, mutation prevalence of BRCA was similar in between Asian and Western women [34]. We found that BRCA1 was highly associated with TNBC which was similar to the finding from the Western studies [22].
A limitation of this study was a short median follow time. The median follow time was 4.67 (range of 0.1 to 22.9) years; however, some results examined were set at a 10-year time frame. In the present study, 718 patients had a follow time more than 10 years. We are following all patients in this cohort and will understand better the impact of BRCA mutation status on the long-term prognosis.
In this study, we provided evidence that our BRCA patients had an increased risk of CBC and second malignancies. The phenomena resemble the cancer risks of other ethnic groups, suggesting that Asian BRCA carriers are a high-risk population susceptible to breast cancer, CBC, and second malignancies. In particular, we found that BRCA1 patients with TNBC as their first cancer had a greater than five-fold risk of developing CBC. Thus, genetic counseling and management of Asian BRCA mutation carriers needs to improve in the future.