full free access: Absence of microsatellite instability in mucinous carcinomas of the breast (Lynch Syndrome)

Note: some key excerpt; see also Supplemental Tables 1-4

"Microsatellite instability (MSI) is a form of genetic instability that results from defects in DNA mismatch repair. MSI is reported to be rare in unselected breast cancers, however it is a common feature in subsets of colorectal, ovarian and endometrial cancers. In these anatomical sites, MSI-high carcinomas often display a mucinous histology. The aim of this study was to determine whether mucinous carcinomas of the breast would more frequently display MSI-high than invasive ductal carcinomas of no special type (IDC-NSTs). The expression of four MSI markers (i.e. MSH2, MSH6, MLH1 and PMS2) was immunohistochemically assessed in 35 mucinous breast carcinomas and 35 histological grade- and oestrogen receptor (ER) status-matched IDC-NSTs, and in a series of 245 invasive breast cancers...........
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Subsets of colorectal [24], gastric [31], pancreatic [31], ovarian [32] and endometrial tumours [22,31,33], and particularly those occurring in the hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome [31], are characterised by microsatellite instability. Interestingly, however, MSI-H appears to be vanishingly rare in breast cancer [21,34]. Likewise, breast cancers displaying an MSI-L status are remarkably rare, whereas in tumours from other anatomical sites, such as colorectal, endometrial or ovarian cancers [27], this phenomenon is not as uncommon. Of note, in some anatomical sites (e.g. colorectal and ovarian), tumours displaying microsatellite instability often display a mucinous histology [32,35,36]. However, the prevalence of MSI in mucinous carcinomas of the breast has not yet been systematically addressed........
...........All 35 pure mucinous carcinomas of the breast analysed were positive for MLH1 and MSH6 as determined by IHC, and 33 out of 35 (94.2%) and 32 out of 34 cases (94.1%) showed expression of MSH2 and PMS2, respectively (Table 2 and Figure 1)............cont'd