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The utility of immunohistochemical detection of DNA mismatch repair proteins in screening colorectal cancer for hereditary nonpolyposis colorectal cancer (HNPCC) is being widely investigated. Currently, in both research and clinical settings, a 4-antibody panel that includes the 4 most commonly affected proteins (MLH1, MSH2, MSH6, and PMS2) is being used generally. On the basis of the biochemical properties of these proteins, we hypothesized that a 2-antibody panel, comprising MSH6 and PMS2, would be sufficient to detect abnormalities in all 4 proteins. We tested this hypothesis on a series of 232 colorectal carcinoma samples derived from 2 patient cohorts: (1) a prospectively accrued series of patients who were judged to carry a higher-than-average risk for HNPCC based on the revised Bethesda guidelines (n=190); and (2) a retrospective series of patients who were 40 years of age or younger (n=42). Immunohistochemical stains were regarded as negative (protein lost), when there was no nuclear labeling in tumor cells (with positive internal control). Overall, 70 of the 232 tumors demonstrated loss of at least one protein. The most common abnormality was concurrent loss of MLH1 and PMS2 (observed in 17% of the cases), followed by concurrent loss of MSH2 and MSH6 (6%). All MLH1 and MSH2-abnormal cases were also abnormal for PMS2 and MSH6, respectively, whereas 9 of 50 (18%) PMS2 and 6 of 20 (30%) MSH6-abnormal cases showed only isolated loss of PMS2 or MSH6 (with normal staining for MLH1 and MSH2). As such, our findings provide evidence that a 2-antibody panel (PMS2 and MSH6) is as effective as the current 4-antibody panel in detecting DNA mismatch repair protein abnormalities. Such a cost-effective approach carries significant implication, as immunohistochemistry is being widely used as first-line screening for HNPCC.

Background: Over 80% of breast cancers in women with germline BRCA1 mutations are estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2-negative ("triple negative") and most of these have a basal-like phenotype by expression profiling and immunophenotypic analysis. However, whether or not expression of biomarkers characteristic of basal-like breast cancers helps to define a subset of women with triple-negative breast cancers who are likely to harbor BRCA1 mutations is an unresolved issue., Methods: We randomly identified 165 women from the Dana-Farber/Harvard Cancer Center SPORE annotated specimen bank with primary invasive, triple-negative breast cancers. Tissue microarrays were constructed by obtaining triplicate 0.6 mm cores from available paraffin blocks from 130 cases: only unstained slides were available for immunostaining from 35 cases. Slides cut from the tissue microarrays and the unstained slides were immunostained for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (to confirm triple-negative status) and for several markers that have been reported to be useful in defining the basal-like phenotype, including basal cytokeratins CK5/6, CK14, and CK17 and epidermal growth factor receptor (EGFR). Full sequencing analysis for BRCA1 germline mutations was performed on blood specimens from all cases. The final study population consisted of 144 cases in which (1) triple-negative status was confirmed; (2) there was sufficient material for analysis of basal cytokeratins and EGFR; and (3) germline BRCA1 mutation status was known., Results: Among these triple-negative breast cancer cases, 97 (67%) expressed one or more basal cytokeratins and 102 (71%) showed EGFR expression. Basal cytokeratin expression was detected in 65% of the tumor from the 20 BRCA1 mutation carriers and in 68% of the cancers from women without mutations (P=NS). EGFR expression was identified in a similar proportion of tumors from women with and without BRCA1 mutations (75% vs. 72%, P=NS)., Conclusions: Basal cytokeratin and EGFR expression are both highly prevalent among triple-negative breast cancers. The frequency of expression of basal cytokeratins and EGFR was similar in women with and without BRCA1 mutations. Therefore, although the expression of basal cytokeratins and/or EGFR can be used to identify triple-negative breast cancers that have a basal-like phenotype, expression of these markers alone is not sufficient to distinguish which women with triple-negative breast cancers are likely to harbor BRCA1 germline mutations.

Despite advances in the treatment of early-stage breast cancer, physicians still lack the ability to accurately predict which individual patients will relapse and would benefit from adjuvant chemotherapy. Traditional clinicopathologic factors are important in helping to determine risk of relapse, but do not fully account for the biologic complexity of breast cancer. Gene-expression profiling has provided us with insight into the heterogeneity of breast cancer and led to the development of prognostic and predictive molecular gene signature models designed to aid in clinical decision-making. However, it remains to be determined how much refinement in prognosis genomic models provide over standard clinicopathologic features and whether these refinements translate into improvements in clinical practice. On-going large prospective multi-center clinical trials will provide us with information regarding the clinical utility of two of these assays, but for now, implementation of these models into widespread clinical practice remains limited.