Background

Women carrying a pathogenic germline mutation in the BRCA1 and BRCA2 genes have an increased lifetime risk of develo** breast, ovarian, and several other cancers [1]. The identification of women harboring mutations in these genes is clinically important and has a significant socio-cultural impact. A major challenge faced by physicians is to identify most appropriate candidates for genetic BRCA1/2 testing since the cost of comprehensive genetic testing can be high and only 3 % of all breast cancers are attributed to BRCA1/2 germline mutations.

The decision to offer genetic testing to a breast cancer patient is currently based on family history of breast/ovarian cancer and age of disease onset. Several prediction models, which consider age of onset and family history of cancer, can be used to estimate the prior probability of having a BRCA1 or BRCA2 mutation [2]. In addition, histopathological tumor parameters can be considered to help predict the presence of a mutation.

Triple negative breast cancer (TNBC) is defined by the absence of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and accounts for 12–15 % of all invasive breast cancer [3]. It occurs most frequently in young women and African-Americans. In Pakistan, 10-year outcome analysis of 636 breast cancer patients registered at a tertiary-care cancer center (Shaukat Khanum Memorial Cancer Hospital and Research Centre - SKMCH & RC) showed that 30.5 % (194/636) of the cases had TNBC; and majority (56.2 %) had their diagnosis made at less than 40 years of age [4]. Patients with TNBC are known to have unfavorable survival compared to patients with other breast cancer subtypes [5].

A large proportion of tumors in women with BRCA1 mutations are associated with the TNBC phenotype [6]. BRCA1/2 mutations have been identified with frequencies varying from 9.4 to 15.4 % in unselected, 17.4 to 49.1 % in younger age and 11.6 to 62 % in high risk patients with TNBC [7–15]. Studies reporting the frequency of BRCA1/2 mutations in TNBC patients from Asia have had several deficiencies including small population size [42] and 11.6 to 62 % [7, 8, 10–13, 15], respectively. The varying mutation frequencies obtained in these studies may be explained by differences in sample size, mutation detection assays used, or ethnic origin of study participants.

The low frequency of BRCA2 mutations detected in our study is in kee** with prior reports and suggests that BRCA2 may not play an important role in the development of early-onset TNBC. With the exception of one small German study that included 30 patients with TNBC [11], BRCA2 mutations were less common than BRCA1 mutations in several studies among patients of European or North-American origin [9, 14, 15, 28] and patients from Asia [7]. As in the study reported by Couch and colleagues, no mutations in the CHEK2 and TP53 genes were observed in two Pakistani studies among 374 (including 103 with TNBC) [46] and 105 (including 47 with TNBC) breast/ovarian cancer patients [47], respectively. Recently, a deleterious mutation (c.5101C > T) in the FANCM gene was identified in BRCA1/2-negative familial patients with TNBC from Finland [48]. This mutation was not detected in a Pakistani study that included 117 patients with TNBC [49].

There are several limitations of our study. First, we have screened only patients with TNBC, who were selected for early-age of onset (≤ 30 years) or family history of breast/ovarian cancer. Hence the selection of high-risk patients may explain the higher BRCA1/2 mutation frequency observed in our study compared to those that evaluated unselected TNBC patients. Secondly, we did not use BRCA1/2 prediction models. However, given the previously observed inaccuracy of these algorithms in predicting risk precisely in Asian populations, limits the usefulness of these algorithms and warrants further investigation [50, 51]. Strengths of the present study include the sample size (N = 523) comprising sufficiently larger number of early-onset breast cancer (≤ 30 years) women (n = 303) with TNBC (n = 131) or non-TNBC (n = 172) compared to studies reported from Asia previously. Additionally, our study evaluated the complete coding regions of the BRCA1 and BRCA2 genes that were comprehensively screened for both, small-range mutations and large genomic rearrangements. Screening for both types of mutations has only been reported in few studies performed previously [10, 26]. Yet another strength was that all data were generated at a single institution, therefore no variability was introduced by using different methods for tumor grading and IHC analysis and evaluation and the pathologist, who evaluated the ER, PR, and HER2 status, was blinded to the mutation status. Finally, the majority of study participants (73.4 %) were recruited within one year of disease presentation, which minimizes the likelihood of survival bias.

Conclusions

We found high prevalence and predominance of BRCA1 germline mutations in Pakistani women with TNBC compared to patients with non-TNBC presenting before or at age 30 irrespective of family history of breast/ovarian cancer and before or at age 50 with familial breast cancer or familial breast and ovarian cancer. The association between TNBC status and presence of BRCA1 mutations was independent of the simultaneous consideration of family phenotype, tumor histology, and tumor grade in a multiple logistic regression model. Our data suggest that TNBC status should be incorporated as a criterion for genetic BRCA1 testing in Pakistan. Identification of individuals with BRCA1 germline mutations will enable physicians to optimize cancer management for this high risk phenotype.