Aberrant promoter methylation of tumor suppressor genes has not been fully investigated in pediatric tumors. Therefore, we examined the methylation status of nine genes (p16 INK4A , MGMT, GSTP1, RASSF1A, APC, DAPK, RARb, CDH1 and CDH13) in 175 primary pediatric tumors and 23 tumor cell lines using methylation-speci®c PCR. We studied the major forms of pediatric tumors ± Wilms' tumor, neuroblastoma, hepatoblastoma, medulloblastoma, rhabdomyosarcoma, osteosarcoma, Ewing's sarcoma, retinoblastoma and acute leukemia. The most frequently methylated gene in both primary tumors and cell lines was RASSF1A (40, 86%, respectively). However, the rates of RASSF1A methylation in individual tumor types varied from 0 to 88%. RASSF1A methylation was tumor speci®c and was absent in adjacent non-malignant tissues. Methylation of the other genes was relatively rare in tumors and nonmalignant tissues (less than 5%). Neuroblastoma patients with methylation of RASSF1A were signi®-cantly older than patients without methylation (P=0.008). There was no relationship between methylation status and other clinico-pathologic parameters. We treated six cell lines lacking RASSF1A mRNA with 5-aza-2'deoxycytidine to examine the relationship between methylation and transcriptional silencing. In ®ve of six cell lines, restoration of RASSF1A mRNA was con®rmed by RT ± PCR. Our ®ndings indicate that aberrant promoter methylation of RASSF1A may contribute to the pathogenesis of many di erent forms of pediatric tumors.

Key Points Question What is the current state of the US pathologist workforce compared with the Canadian pathologist workforce? Findings In this cross-sectional study, a 17.53% decrease in the number of US pathologists was identified from 2007 to 2017. During the same period, there was a 20.45% increase in the number of Canadian pathologists. Meaning Adjusted for population, the US pathologist workforce is now smaller relative to other countries that have experienced major adverse events in clinical laboratory quality and delays in diagnosis.

The unbalanced translocation, der(17)t(X;17)(p11.2;q25), is characteristic of alveolar soft part sarcoma (ASPS). We have recently shown that this translocation fuses the TFE3 transcription factor gene at Xp11.2 to ASPL, a novel gene at 17q25. We describe herein eight morphologically distinctive renal tumors occurring in young people that bear the identical ASPL-TFE3 fusion transcript as ASPS, with the distinction that the t(X;17) translocation is cytogenetically balanced in these renal tumors. A relationship between these renal tumors and ASPS was initially suggested by the cytogenetic finding of a balanced t(X;17)(p11.2;q25) in two of the cases, and the ASPL-TFE3 fusion transcripts were then confirmed by reverse transcriptase-polymerase chain reaction. The morphology of these eight ASPL-TFE3 fusion-positive renal tumors, although overlapping in some aspects that of classic ASPS, more closely resembles renal cell carcinoma (RCC), which was the a priori diagnosis in all cases. These tumors demonstrate nested and pseudopapillary patterns of growth, psammomatous calcifications, and epithelioid cells with abundant clear cytoplasm and well-defined cell borders. By immunohistochemistry, four tumors were negative for all epithelial markers tested, whereas four were focally positive for cytokeratin and two were reactive for epithelial membrane antigen (EMA) (one diffusely, one focally). Electron microscopy of six tumors demonstrated a combination of ASPS-like features (dense granules in four cases, rhomboid crystals in two cases) and epithelial features (cell junctions in six cases, microvilli and true glandular lumens in three cases). Overall, although seven of eight tumors demonstrated at least focal epithelial features by electron microscopy or immunohistochemistry, the degree and extent of epithelial differentiation was notably less than expected for typical RCC. We confirmed the balanced nature of the t(X;17) translocation by fluorescence in situ hybridization in all seven renal tumors thus analyzed, which contrasts sharply with the unbalanced nature of the translocation in ASPS. In summary, a subset of tumors previously considered to be RCC in young people are in fact genetically related to ASPS, although their distinctive morphological and genetic features justify their classification as a distinctive neoplastic entity. Finally, the finding of distinctive tumors being associated with balanced and unbalanced forms of the same translocation is to our knowledge, unprecedented.

Malignant rhabdoid tumors are high-grade neoplasms of the central nervous system (CNS), kidneys and soft tissue that usually occur in children. The histologic diagnosis of malignant rhabdoid tumor depends on identification of characteristic rhabdoid cells-large cells with eccentrically located nuclei and abundant, eosinophilic cytoplasm-and immunohistochemistry with antibodies to vimentin, keratin and epithelial membrane antigen. In most malignant rhabdoid tumors, the SMARCB1/INI1 gene, located in chromosome band 22q11.2, is inactivated by deletions and/or mutations, so genetic diagnosis is often possible. However, tissue may not be available for genetic analysis or studies not confirmatory. We assessed SMARCB1/INI1 expression in 17 rhabdoid tumors and 57 other tumors of the CNS, kidney or soft tissue using immunohistochemistry. In total, 12 brain, three renal and two soft tissue rhabdoid tumors were examined along with four glioblastomas, four pilocytic astrocytomas, four oligodendrogliomas, two ependymomas, two choroid plexus papillomas, five pituitary adenomas, four germinomas, four renal carcinomas with Xp11.2 translocations, two clear cell sarcomas, two Wilms' tumors, one renal medullary carcinoma, two desmoplastic small round cell tumors, two alveolar rhabdomyosarcomas, two embryonal rhabdomyosarcomas, one lowgrade chondrosarcoma, two extraskeletal myxoid chondrosarcomas, one mesenchymal chondrosarcoma, four malignant peripheral nerve sheath tumors, five metastatic carcinomas and four epithelioid sarcomas, two primary and two metastatic. The neoplastic cells of all rhabdoid tumors, the four epithelioid sarcomas and the renal medullary carcinoma did not express SMARCB1/INI1 by immunohistochemistry; neoplastic cells of all other tumors expressed SMARCB1/INI1. Immunohistochemistry to assess expression of SMARCB1/INI1 may be useful in the diagnosis of rhabdoid tumors of the CNS, kidneys and soft tissue.

Two young patients with subacute measles encephalitis are described: a 20-year-old male hemophiliac infected with human immunodeficiency virus (HIV) and a 4-year-old girl with acute leukemia. Both patients were afebrile and had persistent focal seizures and slurred speech beginning 2 and 7 months, respectively, after the onset of uncomplicated acute measles. The diagnosis of subacute measles encephalitis was established by demonstration of paramyxovirus nucleocapsid on electron microscopy of brain tissue in one case and by detection of measles virus genome with the polymerase chain reaction in both. Treatment of the HIV-infected man with intravenous ribavirin was begun when the patient lost consciousness after several weeks of seizures; he died. The girl with leukemia was treated early after the onset of symptoms and recovered after a 15-week course. Review of 31 previously published cases revealed a typical clinical presentation. Cerebrospinal fluid (CSF) analysis, electroencephalography, measurement of measles antibody in serum and CSF, and computed tomography of the brain were not helpful in the diagnosis of subacute measles encephalitis. In contrast, histologic examination of brain tissue proved useful in establishing the diagnosis. On the basis of our experience and our literature review, we conclude that histologic and polymerase chain reaction studies of brain tissue are required for the early diagnosis of subacute measles encephalitis and that therapy with intravenous ribavirin is effective when administered early.

Atypical teratoid-rhabdoid tumor presents at a younger age than medulloblastoma. Although atypical teratoid-rhabdoid tumor and medulloblastoma display similar imaging characteristics on conventional MRI, CPA involvement and intratumoral hemorrhage are more common in atypical teratoid-rhabdoid tumor. If a pediatric posterior fossa mass that displays restricted diffusion is involving the CPA, atypical teratoid-rhabdoid tumor is a more likely consideration than medulloblastoma.

The reappraisal of genetically defined subsets of renal tumors can help to highlight the key pathologic features of specific neoplastic entities. We report the morphologic, immunophenotypic, ultrastructural, and molecular features of 11 renal carcinomas bearing a t(X;1)(p11.2;q21) and/or the resulting PRCC-TFE3 gene fusion. The male/female ratio was 4:7. Ten patients were in the age range of 9-29 years and one was 64 years old (mean 21.3 years, median 15 years). The predominant histologic pattern was nested, with islands of tumor cells compartmentalized by thin-walled capillary vasculature. Minor variations on this pattern yielded solid, acinar, alveolar, and tubular architecture. Papillary architecture was seen in nine cases, usually as a minor component. Neoplastic cells were typically characterized by irregularly shaped nuclei with vesicular chromatin and small nucleoli not visible with a 10x objective, and cytoplasm that ranged from clear to densely granular and eosinophilic. Mitoses were extremely rare; 5 were found in 900 high power fields examined from the 11 neoplasms. The most distinctive immunohistochemical feature of these neoplasms was moderate to intense nuclear labeling for TFE3 protein. These tumors were also consistently immunoreactive for the RCC antigen (10 of 11) and CD10 (9 of 9), whereas cytokeratin and epithelial membrane antigen were negative in four cases and were positive focally in the others. Ultrastructurally, all of the six neoplasms examined showed features consistent with conventional-type (clear cell) renal carcinoma, although two demonstrated distinctive intracisternal microtubules. Both tumors tested contained PRCC-TFE3 fusion transcripts. The differential diagnosis includes conventional-type papillary renal cell carcinoma, conventional-type (clear cell) renal carcinoma, and the ASPL-TFE3 renal carcinomas associated with the t(X;17)(p11.2;q25), with the latter two being morphologically the most similar to the t(X;1) renal carcinomas. Aside from their distinctive clinicopathologic features described here, there is experimental evidence suggesting that these tumors may show differential sensitivity to certain chemotherapeutic agents.

Background. Leiomyosarcoma, a mesenchymal malignancy with smooth muscle differentiation, is extremely rare in children. Immunosuppression, due to either antirejection medication in organ transplantation recipients or human immunodeficiency virus infection (HIV), appears to constitute a predisposition. Methods. Two cases of leiomyosarcoma in pediatric liver transplantation recipients were investigated and compared clinically with respect to site of origin and course of the disease and pathologically by routine histology and electron microscopy, by forensic DNA methodology for origin from donor or recipient tissue, and by EBER‐1 in situ hybridization for evidence of latent Epstein‐Barr virus (EBV) infection. Results. A 9‐year‐old male developed a high grade, poorly differentiated leiomyosarcoma in his allografted liver 2 years after transplantation, and despite antineoplastic chemotherapy, he died of metastatic disease. The genotype of his tumor indicated an origin from allografted tissue. A 12‐year‐old female had a low grade retroperitoneal leiomyosarcoma involving the superior mesenteric vein. After resection, she remained disease free without chemotherapy. The genotype of her tumor indicated an origin from native tissue. In both tumors, latent EBV infection was documented. Conclusions. Neoplastic smooth muscle proliferation in immunosuppressed liver transplantation recipients is analogous to the more common posttransplantation lymphoproliferative disorder in involving transformation of either engrafted donor tissue or recipient tissue elsewhere in the body, in displaying a wide spectrum of histologic differentiation, grade and clinical behavior, and in exhibiting evidence of latent EBV infection.