Is the Mirror Image Method Really Useful in Tumor Tissue Bank Quality Control?

Oncology research projects are highly dependent on the quality of tumor samples stored in the biobank. Microscopic control is important to ensure the quality of the frozen sample (Does the sample correspond to tumor tissue? Does the sample contain a sufficient number of tumor cells for molecular analysis?). The aim of this study was to evaluate the value of the mirror image method in quality control of colonic adenocarcinoma samples stored in a tumor bank. Microscopic concordance for the differentiation grade, malignant and normal cell percentages, necrosis, mucinous component, and ulceration was assessed on 82 colon adenocarcinoma banked samples and their paired, formalin-fixed, paraffin-embedded mirror controls. Molecular concordance for KRAS status was evaluated in 76 of these 82 cases. Morphological correspondence between frozen and mirror samples was good for the mucinous component (intraclass correlation coefficient [ICC] = 0.81), moderate for differentiation (Cohen's kappa coefficient [k] = 0.67), fair for malignant cells (ICC = 0.44), and poor for ulceration (k = 0.08), normal tissue (ICC = 0.36), and necrosis (ICC = 0.13) percentages. Molecular correspondence for KRAS status was almost perfect (95% correspondence, k = 0.88) between frozen and mirror samples. In conclusion, the mirror sample method is not a good alternative for microscopic and molecular control of frozen colonic adenocarcinoma samples.

BRAFV600E Gene Mutation in Colonic Adenocarcinomas. Immunohistochemical Detection Using Tissue Microarray and Clinicopathologic Characteristics: An 86 Case Series.

The detection of BRAF mutation in colorectal cancer has several clinical applications: enabling the discrimination between sporadic and Lynch syndrome-related colorectal carcinoma, and providing warning of a poorer prognosis. Few immunohistochemical studies using whole-tissue tumor section staining have recently been performed on colorectal cancer. The aim of this study was to evaluate the detection of BRAF mutation by immunohistochemistry (IHC) on tissue microarray (TMA). IHC was performed with the BRAF-specific antibody using TMA on a retrospective series of 86 colonic adenocarcinomas with known BRAF status. IHC using BRAF-specific antibody allowed to detect 20/21 BRAF mutated colonic adenocarcinomas and 60/65 BRAF wild-type cases. The staining was equivocal because of equivocal staining in 4 cases and heterogeneity in 3 cases. When compared with TaqMan real-time PCR, the sensitivity and specificity were 95.2% and 92.3%, respectively. Comparison with the whole section immunostaining improved sensitivity to 100% and specificity to 95.4%. Furthermore, in this study we found that BRAF mutated colonic adenocarcinoma were significantly more frequent in women, older patients, and right-sided. Moreover, morphologic features significantly associated with BRAF mutation were: serrated adenocarcinoma subtype, adenocarcinomas with a mucinous component, high histologic grade, pushing margins, stromal inflammation. BRAF-specific antibody can be used on TMA to screen BRAF-mutated colorectal carcinomas. Cases with equivocal or heterogenous staining must be compared with whole section staining. Moreover, BRAF mutated colonic carcinomas have distinct clinical and histopathologic features.

Merkel cell carcinoma: histopathologic and prognostic features according to the immunohistochemical expression of Merkel cell polyomavirus large T antigen correlated with viral load.

Merkel cell carcinoma (MCC) is a neuroendocrine skin malignancy frequently associated with Merkel cell polyomavirus (MCPyV), which is suspected to be oncogenic. In a series of MCC patients, we compared clinical, histopathologic, and prognostic features according to the expression of viral large T antigen (LTA) correlated with viral load. We evaluated the LTA expression by immunohistochemistry using CM2B4 antibody and quantified viral load by real-time polymerase chain reaction. We analyzed formalin-fixed, paraffin-embedded (FFPE) tissue samples (n = 36) and corresponding fresh-frozen biopsies when available (n = 12), of the primary tumor and/or metastasis from 24 patients. MCPyV was detected in 88% and 58% of MCC patients by real-time polymerase chain reaction and immunohistochemistry, respectively. The relevance of viral load measurements was demonstrated by the strong consistency of viral load level between FFPE and corresponding frozen tissues as well as between primary tumor and metastases. From FFPE samples, 2 MCC subgroups were distinguished based on a viral load threshold defined by the positivity of CM2B4 immunostaining. In the LTA-negative subgroup with no or low viral load (nonsignificant), tumor cells showed more anisokaryosis (P = .01), and a solar elastosis around the tumor was more frequently observed (P = .03). LTA-positive MCCs with significant viral load had a lower proliferation index (P = .03) and a longer survival of corresponding patients (P = .008). Depending on MCPyV involvement, 2 MCC subgroups can be distinguished on histopathologic criteria, and the CM2B4 antibody is able to differentiate them reliably. Furthermore, the presence of a significant viral load in tumors is predictive of better prognosis.