Loren E. Clarke

Robust activation of the human but not mouse telomerase gene during the induction of pluripotency

Pluripotent stem cells (PSCs) express telomerase and have unlimited proliferative potential. To study telomerase activation during reprogramming, 3 classes of embryonic stem cell (ESC)‐like clones were isolated from mouse fibroblasts containing a transgenic hTERT reporter. Class I expressed few pluripotency markers, whereas class II contained many, but not Oct4, Nanog, and Sox2. Neither class of cells differentiated efficiently. Class III cells, the fully reprogrammed induced PSCs (iPSCs), expressed all pluripotency markers, formed teratomas indistinguishable from those of mESCs, and underwent efficient osteogenic differentiation in vitro. Interestingly, whereas the endogenous mTERT gene expression was only moderately increased during reprogramming, the hTERT promoter was strongly activated in class II cells and was further elevated in class III cells. Treatment of class II cells with chemical inhibitors of MEKs and glycogen synthase kinase 3 resulted in their further reprogramming into class III cells, accompanied by a strong activation of hTERT promoter. In reprogrammed human cells, the endogenous telomerase level, although variable among different clones, was dramatically elevated. Only in cells with the highest telomerase were telomeres restored to the lengths in hESCs. Our data, for the first time, demonstrated that the hTERT promoter was strongly activated in discrete steps, revealing a critical difference in human and mouse cell reprogramming. Because telomere elongation is crucial for self‐renewal of hPSCs and replicative aging of their differentiated progeny, these findings have important implications in the generation and applications of iPSCs.—Mathew, R., Jia, W., Sharma, A., Zhao, Y., Clarke, L. E., Cheng, X., Wang, H., Salli, U., Vrana, K. E., Robertson, G. P., Zhu, J., Wang, S. Robust activation of the human but not mouse telomerase gene during the induction of pluripotency. FASEB J. 24, 2702–2715 (2010). www.fasebj.org

Clinical validation of a gene expression signature that differentiates benign nevi from malignant melanoma

Histopathologic examination is sometimes inadequate for accurate and reproducible diagnosis of certain melanocytic neoplasms. As a result, more sophisticated and objective methods have been sought. The goal of this study was to identify a gene expression signature that reliably differentiated benign and malignant melanocytic lesions and evaluate its potential clinical applicability. Herein, we describe the development of a gene expression signature and its clinical validation using multiple independent cohorts of melanocytic lesions representing a broad spectrum of histopathologic subtypes.

Interstitial granulomatous drug reaction to anakinra

Interstitial granulomatous drug reactions are an uncommon entity presenting as asymptomatic, annular, erythematous to violaceous plaques. The incidence of such reactions has been increasing with the use of biologic agents. We report, to the best of our knowledge, the first such reaction to the interleukin (IL)-1 inhibitor anakinra. Our patient presented with pink dermal plaques and nodules in the periaxillary region which resolved with discontinuation of anakinra and recurred upon restarting anakinra. Biopsy revealed a diffuse dermal infiltrate of lymphocytes and histiocytes with interspersed neutrophils and eosinophils. Fragmentation and degeneration of collagen and elastic fibers was also present. Withdrawal of anakinra led to complete resolution of the lesions. Interstitial granulomatous drug reactions are increasing in frequency and we add anakinra to the list of causative agents.

Myxofibrosarcoma in the skin

Myxofibrosarcoma, also known as myxoid malignant fibrous histiocytoma, is increasingly recognized as a distinct malignant neoplasm of fibroblastic origin with variable clinical and histopathologic features. Myxofibrosarcomas are among the most common malignant mesenchymal neoplasms of older adults, and approximately two thirds develop within the dermis or subcutis. Herein, we describe the clinicopathologic features of four cases of myxofibrosarcoma involving the skin. Three of these cases were initially misdiagnosed as benign cutaneous neoplasms, two as myxoid neurofibroma. These cases illustrate the clinicopathologic spectrum encompassed by myxofibrosarcoma in the skin and highlight the diagnostic difficulties it may present.

Cutaneous CD34+ Spindle Cell Neoplasms: Histopathologic Features Distinguish Spindle Cell Lipoma, Solitary Fibrous Tumor, and Dermatofibrosarcoma Protuberans

Spindle cell lipoma (SCL), dermatofibrosarcoma protuberans (DFSP), and solitary fibrous tumors (SFT) are cutaneous CD34+ spindle cell tumors that may exhibit histopathologic and immunophenotypic overlap. We sought ways to reliably distinguish among these lesions even in small or superficial biopsies. Ten morphologic characteristics were analyzed in a group of 5 SCLs, 6 cutaneous SFTs, and 12 DFSPs. SFT and DFSP exhibited extensive histopathologic overlap in small or partial biopsies. However, adnexal entrapment, defined as diffuse proliferation of tumor cells around pilosebaceous and eccrine structures with minimal disruption or expansion of the dermis, was a feature seen in 10 of the 12 DFSPs and in none of the SFTs or SCLs. Even when only superficial portions of a lesion were present, this feature was identifiable. Spindle cell lipomas posed little diagnostic difficulty, in part because excisional biopsies were performed in all cases of SCL. The number of samples included in the study is relatively small, in part due to the rarity of cutaneous solitary fibrous tumors. We conclude that careful attention to these histopathologic features enables reliable distinction among these tumors.

CD10‐positive myxofibrosarcomas: a pitfall in the differential diagnosis of atypical fibroxanthoma

CD10 is now commonly used to differentiate atypical fibroxanthoma (AFX) from melanoma, spindle cell and dedifferentiated variants of squamous cell carcinoma and leiomyosarcoma. However, we have encountered CD10‐positive tumors that mimicked AFX but proved to be myxofibrosarcomas. The purpose of this study was to evaluate CD10 expression in a wide range of mesenchymal neoplasms that may involve the skin using tissue microarrays. Our results indicate that in addition to AFX, CD10 expression is common in myxofibrosarcomas, undifferentiated pleomorphic sarcomas, dermatofibromas and dermatofibrosarcoma protuberans. Myxofibrosarcomas commonly present in the skin and may be difficult to distinguish from AFX on small biopsies and CD10 positivity may confound the diagnostic difficulty.

Cutaneous B-cell lymphoma with loss of CD20 immunoreactivity after rituximab therapy

Background:  Antibodies to the B‐cell‐specific antigen CD20 are widely used for immunohistochemical identification of B‐cell lymphomas, approximately 95% of which are strongly CD20‐positive.

Persistent melanocytic nevi: a review and analysis of 205 cases.

Background: Melanocytic nevi can recur or persist if not completely excised and are capable of mimicking malignant melanoma, both clinically and histologically.

Cdc7 expression in melanomas, Spitz tumors and melanocytic nevi.

Background:  Cdc7 is a serine‐threonine kinase required for initiation of DNA replication that may play a role in the development and progression of melanoma.

Basal cell carcinoma characteristics as predictors of depth of invasion.

BACKGROUND Pretreatment risk stratification of basal cell carcinoma (BCC) is largely based on histologic subtype reported from biopsy specimens. OBJECTIVE We sought to determine the degree of concordance between characteristics identified on biopsy specimen and excision and to determine if histologic characteristics other than subtype correlated with depth of invasion. METHODS Histologic specimens of 100 BCC biopsy specimens and corresponding excisions were reviewed. Anatomic site, histologic subtype, maximum depth of extension, contour of the lobules at the leading edge, elastosis characteristics, presence of necrosis, calcification, and ulceration were recorded. Concordance between biopsy specimens and their excisions with relation to depth of tumor lobules was analyzed. RESULTS The concordance between the subtype of biopsy specimen and excision was 62%. Micronodular tumors had the greatest mean depth, followed by infiltrative, nodular, and superficial subtypes. Subtype reported from biopsy specimen (P = .0002) and excision (P < .0001) correlated to depth and was superior to age, contours of excision specimens, the presence of necrosis, and the extent of excisional solar elastosis. Gender, anatomic site, contours of biopsy specimens, elastosis color, elastosis type, the presence of ulceration, and calcification did not correlate with depth. LIMITATIONS Selection bias is present as only standard excisions were included; BCCs treated by other methods were not examined. CONCLUSIONS BCC subtype identified on biopsy specimen may not correlate with subtype identified on excision. Morphologic subtype has the highest correlation with depth and reporting should reflect the highest risk growth pattern if a biopsy specimen contains more than one pattern. Consideration should be given to reporting necrosis and degree of solar elastosis.