The purpose of the present study was to compare the cytotoxicity of mineral trioxide aggregate (MTA) to other commonly used retrofilling materials, Super-EBA and amalgam. This was accomplished using a cell viability assay for mitochondrial dehydrogenase activity in human periodontal ligament fibroblasts after 24-hr exposure to extracts of varying concentrations of the test materials, in both freshly mixed and 24-hr set states. Methyl methacrylate 2% (vol/vol) served as the positive control, and complete culture medium served as the negative control. Differences in mean cell viability values were assessed by ANOVA (p < 0.05). In the freshly mixed state, the sequence of toxicity was amalgam > Super-EBA > MTA. In the 24-hr set state the sequence of toxicity at a low extract concentration was Super-EBA > MTA, amalgam, and Super-EBA > amalgam > MTA at a higher extract concentration. This study supports the use of MTA in the root-end environment.

Molar gestations are defined at the genetic level by their unique parental chromosomal compositions. Their diagnosis, however, currently relies largely on histologic features and on the occasional support of ancillary immunohistochemical and DNA ploidy analyses. We sought to validate DNA genotyping for the routine diagnosis and subtyping of hydatidiform moles (HMs) by analyzing 52 cases of molar pregnancy and their morphologic mimics. DNA was extracted from microdissected chorionic villi and paired maternal endometrial tissue from unstained paraffin sections and analyzed by AmpFlSTR Identifiler PCR Amplification system (Applied Biosystems, Inc). DNA genotyping was informative in all cases with input template DNA amounts ranging from 1.5 to 2.5 ng. Among 38 cases of HMs confirmed by DNA genotyping, there were 26 complete moles with diandric paternal-only genomes (24 homozygous and 2 heterozygous) and 12 partial moles with diandric, monogynic genomes (11 heterozygous and 1 homozygous). All nonmolar cases, including 10 cases of mimics of HM, demonstrated a balanced, biallelic profile of both maternal and paternal origin. Our study demonstrates the applicability of DNA genotyping, the molecular approach for the diagnosis, and subtyping of molar pregnancy, to the daily clinical practice.

RET/PTC1 and RET/PTC3 are the markers for papillary thyroid carcinoma. Their reported prevalence varies broadly. Nonrearranged c-RET has also been detected in a variable proportion of papillary carcinomas. The published data suggest that a wide range in expression levels may contribute to the different frequency of c-RET and, particularly, of RET/PTC detection. However, quantitative expression analysis has never been systematically carried out. We have analyzed by real-time RT-PCR 25 papillary carcinoma and 12 normal thyroid samples for RET/PTC1, RET/PTC3 and for RET exons 10-11 and 12-13, which are adjacent to the rearrangement site. The variability in mRNA levels was marked and four carcinoma groups were identified: one lacking RET/ PTC rearrangement with balanced RET exon levels similar to those of the normal samples (7/25 cases, 28%), the second (6/25 cases, 24%) with balanced RET expression and very low levels of RET/PTC1, the third with unbalanced RET exons 10-11 and 12-13 expression, high RET/PTC1 levels but no RET/PTC3 (7/25 cases, 28%), and the fourth with unbalanced RET expression, high RET/PTC1 levels and low levels of RET/PTC3 (5/25 cases, 20%). Papillary carcinomas with high RET/PTC1 expression showed an association trend for large tumor size (P ¼ 0.063). Our results indicate that the variability in c-RET and RET/PTC mRNA levels contributes to the apparent inconsistencies in their reported detection rates and should be taken into account not only for diagnostic purposes but also to better understand the role of c-RET activation in thyroid tumorigenesis. Oncogenic c-RET activation in thyroid tumors composed of follicular cells is the result of chromosomal rearrangements resulting in the fusion of the RET tyrosine-kinase (RET-TK) domain to the 5 0 -terminal region of heterologous genes. The rearrangements are a molecular marker for papillary thyroid carcinoma as their very name, RET/PTC for papillary thyroid carcinoma, implies, 1 and consist of balanced inversions or translocations that involve the 3.0 kb intron 11 of c-RET. To date, at least 16 chimeric mRNAs affecting 11 different genes have been reported (Saenko et al, 2 reviewed in Tallini and Asa 3 ), of which RET/PTC1 (consisting of the fusion of RET with H4) and RET/PTC3 (consisting of the fusion of RET with RFG/ELE1) are by far the most common. 3 Their prevalence varies broadly from zero to more than 60% in nonradiation-associated cases 3 and is close to 90% in some series of papillary carcinomas from the Chernobyl area diagnosed after the 1986 nuclear disaster. 4 While the high prevalence of RET/PTC in radiation-associated thyroid tumors is consistent with misrepair of radiationinduced double-strand DNA breaks, 5,6 the high variability in the prevalence of RET/PTC in sporadic tumors has no specific explanation. In addition to rearranged RET forms, c-RET expression has also been identified in a highly variable proportion of papillary carcinoma samples. Although its signifi-

Poorly differentiated carcinoma of the thyroid gland (PDC) represents an heterogeneous group of epithelial neoplasms with morphologic features and clinical characteristics intermediate between well differentiated and anaplastic (undifferentiated) carcinomas. Unlike well differentiated tumors, PDCs are associated with significant morbidity and mortality. The general prevalence of RET/PTC rearrangement in thyroid PDC and its impact on patient outcome are unknown. To address these issues and to identify prognostically relevant clinicopathologic parameters, we have investigated a series of 62 PDCs. RET/PTC rearrangement, analyzed by RT-PCR and immunohistochemistry using antibodies specific for the tyrosine kinase and juxtamembrane portions of the RET protein, was identified in 8/62 (12.9%) PDCs. RET/PTC was more common in cases with histologic evidence indicating coexistence with or possible evolution from a well differentiated papillary carcinoma (5 of 25 tumors, 20%) but did not correlate with other clinicopathologic parameters. The relatively low prevalence of RET activation in PDCs argues against a major role for RET/PTC in the progression from well to poorly differentiated thyroid tumor phenotypes. Survival analysis demonstrates that poor survival in PDC is associated with old age, male sex, invasion of extrathyroidal soft tissues, coexistence in the same tumor of oncocytic features with insular growth pattern, and distant metastases but not RET activation.

Histological separation of synovial sarcomas from malignant peripheral nerve sheath tumors can be difficult and available immunohistochemical markers sometimes give rise to overlapping staining patterns. Additional markers are needed to better define the two entities in the routine surgical pathology practice. To this end, we explored diagnostic applications of HMGA (HMGA1 and HMGA2) protein immunohistochemistry in comparable groups of synovial sarcoma and malignant peripheral nerve sheath tumors. The histological diagnosis of these cases was confirmed by the presence or absence of synovial sarcoma specific SYT-SSX fusion transcript analyzed by real-time reverse transcription polymerase chain reaction. In all, 13 malignant peripheral nerve sheath tumors and 15 synovial sarcomas were included in this study. Immunohistochemically, most malignant peripheral nerve sheath tumors expressed both HMGA1 and HMGA2 protein (12/13 and 12/13 cases, respectively) with moderate to strong nuclear staining patterns. Most cases of synovial sarcomas demonstrated variable expression of HMGA1. However, significant immunoreactivity for HMGA2 was present in the glandular component of a biphasic tumor (1/1) and rarely detected in monophasic synovial sarcomas (1/14). In summary, expression of HMGA2 is a feature of MPNST but not of synovial sarcoma and immunohistochemical staining of HMGA2 may be a useful marker to separate malignant peripheral nerve sheath tumor from synovial sarcoma. Modern Pathology (2005) 18, 1519-1526.