Bistranded oxidative clustered DNA lesions are closely spaced lesions (1-10 bp) that challenge the DNA repair mechanisms and are associated with genomic instability. The endogenous levels of oxidative clustered DNA lesions in cells of human cancer cell lines or in animal tissues remain unknown, and these lesions may persist for a long time after irradiation. We measured the different types of DNA clusters in cells of two human cell lines, MCF-7 and MCF-10A, and in skin obtained from mice exposed to either 12.5 Gy or sham X radiation. For the detection and measurement of oxidative clustered DNA lesions, we used adaptations of number average length analysis, constant-field agarose gel electrophoresis, putrescine, and the repair enzymes APE1, OGG1 (human) and Nth1 (E. coli). Increased levels of all cluster types were detected in skin tissue from animals exposed to radiation at 20 weeks postirradiation. The level of endogenous (no radiation treatment) oxidative clustered DNA lesions was higher in MCF-7 cells compared to nonmalignant MCF-10A cells. To the best of our knowledge, this is the first study to demonstrate persistence of oxidative clustered DNA lesions for up to 20 weeks in animal tissues exposed to radiation and to detect these clusters in human breast cancer cells. This may underscore the biological significance of clustered DNA lesions.

ContextLow-grade appendiceal mucinous neoplasm (LAMN) and appendiceal adenocarcinoma are known to cause the majority of pseudomyxoma peritonei (PMP, i.e. mucinous ascites); however, recognition and proper classification of these neoplasms can be difficult despite established diagnostic criteria.ObjectiveTo determine the pathological diagnostic concordance for appendix neoplasia and related lesions during patient referral to an academic medical center specialized in treating patients with PMP.DesignThe anatomic pathology laboratory information system was searched to identify cases over a two-year period containing appendix specimens with mucinous neoplasia evaluated by an outside pathology group and by in-house slide review at a single large academic medical center during patient referral.Results161 cases containing appendix specimens were identified over this period. Forty-six of 161 cases (28.6%) contained appendiceal primary neoplasia or lesions. Of these, the originating pathologist diagnosed 23 cases (50%) as adenocarcinoma and 23 cases (50%) as LAMN; however, the reference pathologist diagnosed 29 cases (63.0%) as LAMN, 13 cases (28.3%) as adenocarcinoma, and 4 cases (8.7%) as ruptured simple mucocele. Importantly, for cases in which the originating pathologist rendered a diagnosis of adenocarcinoma, the reference pathologist rendered a diagnosis of adenocarcinoma (56.5%, 13 of 23), LAMN (39.1%, 9 of 23), or simple mucocele (4.3%, 1 of 23). The overall diagnostic concordance rate for these major classifications was 71.7% (33 of 46) with an unweighted observed kappa value of 0.48 (95% CI, 0.27–0.69), consistent with moderate interobserver agreement. All of the observed discordance (28.3%) for major classifications could be attributed to over-interpretation. In addition, the majority of LAMN cases (65.5%) had potential diagnostic deficiencies including over-interpretation as adenocarcinoma and lacking or discordant risk stratification (i.e. documentation of extra-appendiceal neoplastic epithelium).ConclusionsAppendiceal mucinous lesions remain a difficult area for appropriate pathological classification with substantial discordance due to over-interpretation in this study. The findings highlight the critical need for recognition and application of diagnostic criteria regarding these tumors. Recently published consensus guidelines and a checklist provided herein may help facilitate improvement of diagnostic concordance and thereby reduce over-interpretation and potential overtreatment. Further studies are needed to determine the extent of this phenomenon and its potential clinical impact.

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Merkel cell carcinoma was originally reported as neuroendocrine carcinoma of the skin. Merkel cell carcinoma of the ear canal is extremely rare. The aims of the present study are to report the expression of the Merkel cell polyomavirus in a case of CK20-negative primary Merkel cell carcinoma of the ear canal and to study the expression of CM2B4 (Santacruz Biotechnology, CA) monoclonal antibody in primary and metastatic Merkel cell carcinoma in our database. CM2B4 is a mouse monoclonal antibody to Merkel cell polyoma virus (MCPyV). Nine cases of Merkel cell carcinoma were retrieved from our database from 2007 to 2012. Cases studied were 4 primary Merkel cell carcinomas of skin, 1 primary Merkel cell carcinoma of the ear canal, 1 primary Merkel cell carcinoma of the nose, and 3 cases of metastatic Merkel cell carcinoma. All cases were formalin fixed and paraffin embedded. Immunohistochemistry was performed on 3-µm-thick sections cut from selected paraffin blocks. Immunohistochemistry for cytokeratin 20 and polyoma virus was performed in all cases. All cases were positive for CM2B4 except 1. Merkel cell carcinoma of the ear canal was positive for CK8/18 in a paranuclear dot pattern, negative for CK20, and positive for CM2B4. Because of the rarity of the disease, our cohort is small. However, we find that CM2B4 immunohistochemistry has an important role in the diagnosis of Merkel cell carcinoma and corroborates the histopathologic diagnosis in CK20-negative cases.