American Society for Clinical Pathology: Molecular Testing in Colorectal Cancer (Lynch Syndrome/MLH1, MSH2, MSH6, PMS2/MSI-H/KRAS/BRAF.....)

Blogger's Note: focus (obviously) on colorectal cancer, however, the cancer spectrum of Lynch Syndrome is noted in this paper as well as the shortcomings of the Bethesda Guidelines

 Molecular Testing in Colorectal Cancer

Conclusion

In summary, current standard-of-care molecular testing of CRC is aimed at detecting Lynch syndrome and KRAS mutations. However, with recent rapid development of biological agents targeted against components of the EGFR signaling cascade in the treatment of CRCs, mutational analysis of the genes in the EGFR signaling pathway may become a standard of care for patients with CRC in the near future. Ideally, identifying molecular prognostic and predictive factors may allow us to identify high-risk patients with stage II CRC who will benefit from chemotherapy after surgery. In addition, this may allow us to determine patients’ eligibility for targeted biological therapies.

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

full access 2008: Systematic Review and Meta-analysis of Ovarian Cancers: Estimation of Microsatellite-High Frequency and Characterization of Mismatch Repair Deficient Tumor Histology

Translational Relevance:

This systematic review and meta-analysis estimates the frequency of high-level microsatellite instability (MSI-H) in unselected ovarian cancers as 12%, suggesting that defects in the mismatch repair (MMR) pathway account for a relatively large proportion of ovarian cancers. In the era of personalized medicine, MSI-H status may provide valuable etiologic and diagnostic information, which may eventually be of prognostic and therapeutic utility, as seen in MSI-H colorectal cancers.

The results of this meta-analysis also reveal an overrepresentation of nonserous histologies in MMR-deficient tumors. The clinical relevance of these findings is that they may increase clinical awareness of MMR-deficient tumors; such awareness may aid in the identification of this subtype of tumors, having potential implications for medical management.