Basal-like breast carcinoma represents a distinctive group of invasive breast carcinomas with specific genotype and immunoprofile. It is associated with poor prognosis and currently no targeted therapy is available. There are limited numbers of studies investigating morphological features of BLBCs and to date, detailed clinicopathologic characteristics of the basal-like carcinomas have not been described in Turkish population [9, 10, 22, 23].
Genetic, ethnic and racial factors influence breast carcinoma molecular subtypes, possibly by determining intrinsic differences in tumor biology . Basal-like breast carcinomas are more frequent in African Americans (26.5%) and in African women (34%) than Non-African Americans (16.0%) [7, 24]. The incidence was lower in studies from Asia, including Korea, China and Japan (14.7%, 12.6% and 8.4%, respectively) [25–27]. This study, in which we believed that the Turkish population can be reflected, only 45 out of 468 patients with invasive breast carcinomas (9.6%) exhibited basal-like immunophenotype. This incidence rate was similar to the reported incidences from the east part of the world and an earlier study from Turkey .
Invasive ductal carcinoma was the most frequent histological subtype identified for the BLBCs in this study (76.59%), in accordance with the literature [7, 10, 27, 28]. Although basal-like tumors were usually shown to have worse prognosis [4, 16], several studies have also revealed that carcinomas known to have a good prognosis, such as invasive lobular carcinoma, adenoid cystic carcinoma and tubular carcinomas, may also show basal-like phenotype [29–31]. Most of the medullary carcinomas with their favourable outcome, also, had basal-like phenotype with both GEP and immunohistochemistry [32–34]. The incidence of metaplastic carcinomas showing basal-like features ranges from 75 to 95% in the literature [27, 35, 36]. In this study, none of the invasive lobular carcinoma and tubular carcinoma cases was BLBC, but all of the medullary carcinomas (100%) and 56% of the metaplastic carcinomas had basal-like immunophenotype. A pleomorphic carcinoma was also classified as BLBC according to IHC results.
In two studies, using GEP, average age of basal-like carcinomas was detected as 46 and 59 years, respectively [7, 37]. In this study, the youngest patient with BLBC was 19 and the oldest was 78 years old. We observed that BLBCs were seen in slightly younger patients compared to NBBCs (49.3 versus 53.3 years, p=0.04).
Tumor size, lymph node metastasis, local invasion are important prognostic factors for breast carcinomas. In most of the studies, it has been shown that BLBCs had larger tumor size and a tendency for visceral metastases instead of lymph node metastases [27, 28, 38–44]. However, contradictory observations were also present [9, 37, 45]. In this study, the size of BLBCs was ranged from 1 to 8 cm, with an average of 2.8 cm, with no difference from NBBCs (p=0.47). Lymph node metastasis rate for BLBCs and NBBCs were similar (54.6% versus 56.4%, respectively, p=0.51).
Identification of multifocality or bilaterality in breast carcinomas is not uncommon [46, 47]. Patients with multiple tumor foci display higher incidence of lymph node positivity than unifocal tumors [46, 48]. Tot et al. found that basal-like carcinomas and basal keratin positive breast tumors are often multifocal (28% and 48%, respectively) . There is only one study that investigated the relationship between bilateral breast carcinomas and molecular subtypes and found that basal-like tumors are frequently discordant with their contra lateral counterparts . Another study showed that contra lateral breast cancer occurred in 25% of recurrences of basal-like tumors . In this study, among 468 patients, 13 had bilateral breast carcinomas, containing 11 synchronous and 2 metachronous tumors; and another 15 patients had multifocal tumor foci in the same breast. In 2 synchronous bilateral breast carcinomas, there were discordance between tumor pairs; one side had basal-like immunophenotype while the contra laterals did not. One of these NBBCs was ER and PR positive, while the other one was TN, and both of them did not express basal keratins, EGFR or vimentin. Two patients with more than one tumor foci in the ipsilateral breast had multifocal BLBC. One of these patients had 4 foci, 2 of which were BLBCs while the other two were TN carcinomas without expression of basal keratins, EGFR or vimentin. Other patient had 2 tumor foci and both were BLBCs. Despite of same hormonal and environmental influences on the ipsilateral and/or contralateral breast, this heterogeneity may support a stem cell hypothesis on carcinogenesis in which continuing mutations may result in development of different types of carcinomas. We believe that studies in which stem cell surface markers are being investigated should be constructed to highlight this issue.
The typical histological appearance of BLBCs has been reported to be a circumscribed, solid lesion with pushing border and a large central ‘geographic’ necrosis or sclerosis. They have nuclear pleomorphism with high histological grade and high mitotic rate (usually more than 40–45 mitosis per 10 HPFs), consistent with their aggressive behavior [7, 9, 10, 27, 28, 37, 50]. Other common morphological features are stromal lymphocytic response, tumor cells with high nucleus to cytoplasmic ratio, vesicular chromatin and prominent nucleoli [9, 10, 23, 42, 45].
All basal-like tumors, we have analyzed in this study, were grade 3 with a specificity of 70.2%. The mitotic rate was also prominently increased, 93% of basal-like tumors had 15 mitoses and more per 10 HPFs (ranging from 8 to 60 mitoses/10 HPFs). Most of the tumor cells were generally disposed in nests, ribbon like and solid structures with a tubular score of 3 (93.6%). All except one (97.9%), BLBCs had a nuclear grade of 3. All of the grading factors were statistically determinant for BLBC (p<0.0001), supporting that BLBCs are solid, high-grade tumors with high mitotic count and pleomorphic-atypical nuclei. In this study, both geographic and central necroses were more common in BLBC than NBBC (respectively, 40.4% vs. 14.5% and 66% vs. 16.1%, p<0.0001). We observed that large, central acellular zones can be found in BLBCs, in contrast to the findings of Livasy et al. , although it was not a discriminator morphology for them (p=0.68). Consistent with the literature [9, 10, 23], any degree of stromal lymphocytic response was the most common morphological feature for BLBCs among others investigated in this study (91.5%). Similarly, patients with basal-like carcinoma had increased tendency to grow with pushing borders than NBBC (57.5% versus 15.9% respectively, p<0.0001). Although CIS is regarded as a precursor lesion for most of the invasive breast carcinomas , the reported incidence of accompanying CIS in BLBCs is low [23, 48, 51]. Compatible with these data, CIS did not accompany to 57.4% of the BLBCs in this study, supporting the idea that BLBC transforms to invasive cancer in an early period, without remaining in pre-invasive CIS stage. The amount of the cytoplasm of the tumor cells did not show a meaningful difference between BLBCs and NBBCs in this study (p=0.27). As a summary, BLBCs exhibits these main histological characteristics: high histologic and nuclear grade, lack of tubule formation, frequent mitotic figures, central and geographic necrosis, pushing tumor borders and lymphocytic infiltrate. Cytologically, they have prominent nucleoli and nuclear vesicular chromatin. Carcinoma in situ usually does not accompany to the tumor. Among these features, on multivariate analyses, the most important factors were mitotic number (OR: 1.098, p<0.0001), vesicular chromatin (OR: 4.250, p=0.004), tubule grade (OR: 5.361, p=0.011), stromal lymphocytic response (OR: 4.177, p=0.031) and absence of CIS (OR: 2.344, p=0.039). Fulford et al. also performed multivariate analyses and reported that presence of squamous metaplasia, central scar, tumor necrosis, high mitotic count and absence of prominent cytoplasm are strongly associated with BLBC .
Although most of the BLBCs are TN, approximately 71-85% of TN carcinomas have basal-like phenotype [11, 52–54]. In this study, BLBCs constituted 79.7% of TN carcinomas and this proportion was in the reported range from previous studies.
Immunohistochemical markers, such as mammoglobulin, ER, PR and CK7, can be used for the detection of breast origin of a tumor . Some other markers, such as CK5/6 and CK14, have been shown to be independently associated with poor outcome when expressed in breast carcinomas. In non-neoplastic breast ducts, these two markers are also expressed in the basal layer, so called basal CKs [56–59]. In this study, 27.6% of the BLBCs were immunoreactive to CK14 and 95.7% were to CK5/6. It should be noted that CK5/6 and CK14 expressions were also identified 46.8% and 7.7% of NBBCs. Restricted expression of CK14 to mature myoepithelial cells and the broader expression of CK5/6 in bi-potential progenitor cells may explain the difference in basal keratin expression in the tumors . However, the frequency of CK5/6 expression in our study was much higher than the reported series in the literature [28, 56, 57]. On the other hand, it has been known that basal CKs are not expressed in all basal-like tumors classified by gene microarray analysis . Therefore, we actually need additional IHC markers to identify basal-like tumors. Epidermal growth factor receptor (EGFR) is a member of the c-ERB-B family of tyrosine kinase receptor proteins, and has a role in tumor cell survival and proliferation . An association between EGFR expression and the basal like phenotype has been demonstrated in several studies [10, 11]. The expression rates for EGFR ranged from 5% to 65% in breast carcinomas and from 45% to 72% in BLBCs, depending on the methodology used in different studies [10, 11, 27, 62–64]. Shao et al. also showed that immunohistochemical expression of EGFR correlated with and predicted EGFR amplification . In this study, 51.3% of BLBCs were EGFR positive, whereas only 11% of NBBC cases expressed EGFR. This high percentage of EGFR expression in BLBCs is important, not only for the diagnosis of BLBCs, but also in the treatment of this high grade and TN cancers . Lv et al. showed that EGFR gene amplification is more frequent than EGFR gene mutations . We believe that potentially promising anti-EGFR therapies should be introduced for the cases in which gene copy numbers were examined by molecular studies for now, similar to c-ERB-B2.
Vimentin expression in breast carcinomas may have an association with poor prognosis, hormone receptor negativity and co-expression of EGFR, which are consistent features for basal-like tumors [66, 67]. In several studies, more than 90% of the basal-like carcinomas were found to have diffuse and strong vimentin expression [10, 68]. In our series, 53.2% of BLBCs were immunoreactive to vimentin, while 9.5% of NBBCs also showed positivity (p<0.0001). In accordance with the basal CKs, myoepithelial or stem cell origin and epithelial to mesenchymal transition can explain the vimentin expression in basal-like tumors . In this study, vimentin had a concordance of 54.2% with CK5/6 and 79.4% with EGFR (p<0.0001) for BLBCs. If vimentin or CK14 were included in the IHC panel for identifying basal-like tumors, three more TN cases would be considered as BLBCs. Moreover, these high-grade tumors had similar architectural and/or cytological features to BLBCs. Therefore; we suggested that vimentin and CK14 could be added to the diagnostic panel of antibodies to increase the diagnostic accuracy of basal-like tumors. Moreover, using integrating digital image analysis, while evaluating multiple IHC markers, can help to determine subgroups of breast carcinomas more accurate .