Intrinsic histological abnormalities of aortic root and ascending aorta in tetralogy of Fallot: evidence of causative mechanism for aortic dilatation and aortopathy.

BACKGROUND: Dilatation of the aortic root is a known feature in tetralogy of Fallot (TOF) patients with pulmonary stenosis (PS) or pulmonary atresia (PA). We hypothesized that intrinsic histological abnormalities of the aortic wall present since infancy are an important causative factor leading to aortic root dilatation. METHODS AND RESULTS: We examined the aortic histology of 17 cases with TOF and PS/PA from our cardiac morphology archive and compared them with a control group of normal aortas. Measured circumference of the aortic root at the sinotubular junction and at the ascending aorta was indexed to the left ventricle. Aortic walls were studied by light microscopy with the use of various stains. Seventeen TOF cases (7 with PS, 10 with PA) including 7 infants, 2 children, and 8 adults were compared with 11 hearts with normal aorta. Aortic root circumference to left ventricular index and ascending aortic circumference to left ventricular index were 1.24+/-0.25 and 1.37+/-0.24, respectively, in the TOF group versus 0.89+/-0.10 and 0.88+/-0.11, respectively, in the control group (P<0.001). Histological changes of grade 2 or 3 were present in 29% (medionecrosis), 82% (fibrosis), 35% (cystic medial necrosis), and 59% (elastic fragmentation) in the ascending aorta of the TOF group. Histology grading scores were significantly higher in the TOF group (median score, 7; range, 1 to 12) compared with normal controls (median score, 2; range, 0 to 6) and correlated with the ascending aortic circumference to left ventricular index (r=0.525, P=0.03). CONCLUSIONS: There are marked histological abnormalities in the aortic root and ascending aortic wall of patients with TOF present from infancy, suggesting a causative mechanism for subsequent aortic root dilatation.

An E mu-BCL-2 transgene facilitates leukaemogenesis by ionizing radiation.

Clonogenic murine B cell precursors are normally ultrasensitive to apoptosis following genotoxic exposure in vitro but can be protected by expression of an E mu-BCL-2 transgene. Such exposures are likely to be mutagenic. This in turn suggests that a level of in vivo genotoxic exposure that usually has minimal pathological consequences might become leukaemogenic when damaged cells fail to abort by apoptosis. If this were to be the case, then the cell type that becomes leukaemic and the chromosomal/molecular changes that occur would also be of considerable interest. We tested this possibility by exposing E mu-BCL-2 and wild-type mice of differing ages to a single dose of X-irradiation of 1-4 Gy. Young (approximately 4-6 weeks) transgenic mice developed leukaemia at a high rate following exposure to 2 Gy but adult mice (4-6 months) did not. Exposure to 4 Gy produced leukaemia in both young and adult transgenic mice but at a higher frequency in the former. Leukaemic cell populations showed clonal rearrangements of the IGH gene but in most cases analysed had immunophenotypic features of an early B lympho-myeloid progenitor population which has not previously been recorded in radiation leukaemogenesis. Molecular cytogenetic analysis of leukaemic cells by banded karyotype and FISH revealed a consistent double abnormality: trisomy 15 plus an interstitial deletion of chromosome 4 that was confirmed by LOH analysis.

An improved method for detection of B-lymphoid clonality by polymerase chain reaction.

Several groups have recently described methods for the detection of clonal immunoglobulin heavy chain (IgH) gene rearrangements in B-cell malignancies by polymerase chain reaction (PCR) gene amplification using variable region-(VH) and joining (JH) region-specific primers. The simplest methods utilize a single VH primer specific for sequences present in most VH regions corresponding to the third framework region (FR3). An alternative approach is to use a panel of VH family-specific primers specific for the first framework regions (FR1). In the course of nucleotide sequence analysis of IgH gene rearrangements amplified using a VH FR1 primer panel, these authors previously observed 3' VH region deletion and/or base mis-matches sufficient to prevent efficient priming from the VH FR3 primer target sequence in a significant minority of cases of B-lineage malignancy. An improved PCR method has therefore been developed by using a panel of seven VH FR1 family-specific primers incorporated in a single reaction. By using this method clonal IgH gene rearrangement is detected in 15 of 16 cases of B-lineage malignancy. Significantly, this series included four cases of B-lymphoma in which previous attempts to detect PCR clonal IgH gene rearrangements using a VH FR3 primer were unsuccessful. In two of these cases, nucleotide sequence analysis of the amplified DNA showed that failure to prime with the VH FR3 primer was likely to be attributable to insufficient homology with the target sequence. The use of the approach described in this paper should significantly improve the reliability of detection of B-lymphoid clonality by PCR.

Intratracheal administration of recombinant human factor IX (BeneFix) achieves therapeutic levels in hemophilia B dogs.

The purpose of this paper was to establish proof of concept for administration of human recombinant F.IX (rF.IX) by inhalation for therapy of hemophilia B. The pharmacokinetics of intratracheal (IT) administration of rF.IX was studied in nine hemophilia B dogs randomized into 3 groups that received 200 IU/kg IT, 1,000 IU/kg IT, or 200 IU/kg intravenously (IV). IT rF.IX produced therapeutic levels of F.IX antigen and activity and the pharmacokinetic parameters were consistent with a slow release from a depot site within the lungs. Bioavailability compared to IV administration was 11% for 200 IU/kg IT and 4.9% for 1,000 IU/kg. The whole blood clotting time began to shorten at 2 h but F.IX bioactivity was not detected until 8 h post infusion in both IT groups. In all groups, F.IX activity was detected through 72 h post administration. These data demonstrate that biologically active rF.IX can reach the systemic circulation when given IT. Aerosolization of rF.IX may provide a needle-free therapeutic option for delivery of rF.IX to hemophilia B patients.

Granulocytic sarcoma: misleading immunohistological staining with MT1 and S100 protein antibodies.

Tissue from two patients with granulocytic sarcomas stained positively for MT1 and S100 protein antibodies; both of these cases presented considerable clinical and histological diagnostic difficulties until acute myeloblastic leukaemia spread to the bone marrow. Tissues from a further eight patients with granulocytic sarcoma were also examined retrospectively. Seven of them stained for MT1 and four for S100 protein but the traditional histological markers for myeloid cells--chloroacetate esterase and lysosyme--often stained only weakly and focally. This pattern of staining should raise the possibility of a granulocytic sarcoma in otherwise problematic cases.

Rapid method for distinguishing clonal from polyclonal B cell populations in surgical biopsy specimens.

The polymerase chain reaction (PCR) was used to detect clonal rearrangements of the immunological heavy chain gene in frozen samples of human lymphoid tissue. DNA sequences in rearranged genes were amplified using oligomeric primers predicted from conserved sequences in the variable (VH) and joining (JH) regions. On polyacrylamide gel electrophoresis, polyclonal B cell proliferations showed a "smear", probably due to the variable lengths of the diversity (DH) region genes and the N regions separating the VH and DH and JH regions. In contrast, DNA from B cell lymphomas showed a clear single band in eight out of 10 cases. PCR undertaken on germ line DNA from non-lymphoid tumours showed no detectable bands or smears. The method can be completed within one day of biopsy, compared with several days in the case of conventional DNA blot analysis. Furthermore, it is cheaper, simpler, avoids the need for radioactive materials and requires very small amounts of DNA (about 1 micrograms).

Evaluation of sensitivity, specificity, and reproducibility of an optimized method for detecting clonal rearrangements of immunoglobulin and T-cell receptor genes in formalin-fixed, paraffin-embedded sections.

Following our recent reports of detecting clonal immunoglobulin and T-cell receptor gene rearrangements by the polymerase chain reaction, we have improved and simplified the technique for use in diagnostic histopathology laboratories and determined, on coded samples, the sensitivity, specificity, and reproducibility of the modified methodology in distinguishing malignant lymphoma from reactive lymphoid hyperplasia and nonlymphoid tumors. Using only three primer pairs for the immunoglobulin heavy chain and T-cell receptor beta and gamma chain genes on well-characterized lesions of widely varying morphology and immunophenotype, clonal rearrangements were detected in 65% of B-cell lymphomas, and 77-82% of T-cell tumors. Specificity and observer consistency ranged from 93-97%. The method requires very careful control, particularly to avoid misinterpretation of results because of contamination and nonspecific amplification, but in its present form is relatively simple and inexpensive, and gives results on single paraffin-embedded sections within 24 h.

A simplified method of detection of clonal rearrangements of the T-cell receptor-gamma chain gene.

A series of T-cell proliferations in peripheral blood, bone marrow, or tissue samples, together with seven T-cell lines, were analysed for clonality. The technique used employs the polymerase chain reaction (PCR) to amplify rearranged T-cell receptor gamma genes, using primers recognising conserved sequences in the variable and joining gene segments. Of the 20 cases of T-cell leukaemia or lymphoma analysed, a clone was detected in 14 (70%): Of seven T-cell lines, a clone was detected in 6 (84%). No positive results were recorded in eight non-T-cell disorders (including nonlymphoid malignancies and reactive disorders). When the results of this technique were combined with the results of our previously published method for the detection of clonally rearranged T-cell receptor-beta (TCR-beta) genes using PCR, 9 of 10 (90%) T-cell tumours were detected. This method uses only four primer combinations in two tubes, and is therefore simple and rapid: it requires no radiolabelling, uses only a small amount of tissue, and can be performed on formalin-fixed, paraffin-embedded tissue.

Pulmonary vein stenosis: the UK, Ireland and Sweden collaborative study.

OBJECTIVE: To describe clinical features, morphology, management and outcome of pulmonary vein stenosis (PVS) in childhood. DESIGN AND SETTING: Retrospective international collaborative study involving 19 paediatric cardiology centres in the UK, Ireland and Sweden. PATIENTS: Cases of PVS presenting between 1 January 1995 and 31 December 2004 were identified. Cases where pulmonary veins connected to a morphological left atrium were included. Functionally univentricular hearts and total anomalous pulmonary venous connection were excluded. All available data and imaging were reviewed. RESULTS: 58 cases were identified. In 22 cases (38%) there was premature delivery. 46 (79%) had associated cardiac lesions; 16 (28%) had undergone previous cardiac surgery before PVS diagnosis. 16 children (28%) had a syndrome or significant extracardiac abnormality. 36 presented with unilateral disease of which 86% was on the left. Where there was adequate sequential imaging, disease progression was shown with discrete stenosis leading to diffusely small pulmonary veins. Collateral vessels often developed. 13 patients had no intervention. Initial intervention was by catheter in 17 and surgery in 28. Overall 3-year survival was 49% (95% CI 35% to 63%) with patients undergoing initial surgical intervention having greater freedom from death or re-intervention (hazard ratio 0.44, 95% CI 0.2 to 0.99, p = 0.023). CONCLUSIONS: PVS is a complex disease of uncertain cause and frequently associated with prematurity. Early intervention may be indicated to deter irreversible secondary changes.

Occluding the left atrial appendage: anatomical considerations.

BACKGROUND: Occlusion of the left atrial appendage (LAA) is thought to reduce the risk of thromboembolic events in patients with atrial fibrillation. OBJECTIVE: To examine the LAA and its relationship to neighbouring structures that may be put at risk when intervening to occlude its os. METHODS: 31 heart specimens were examined grossly. Four of the LAAs were processed for histological examination and endocasts were made from 11 appendages. The diameters of the LAA os and proximity to the left superior pulmonary vein, mitral valve and left anterior descending artery were measured and areas of thin atrial wall in the vicinity were noted. RESULTS: The LAA orifice was oval shaped in all cases with a mean (SD) diameter of 17.4 (4) mm (range 10-24.1). The mean (SD) distances of the LAA orifice to the left superior pulmonary vein and mitral valve were 11.1 (4.1) mm and 10.7 (2.4) mm, respectively. The left anterior descending, circumflex artery and, in 6 cases, the sinus node artery, were in close proximity to the LAA. Pits or troughs and areas of thin atrial wall were found in 57.7% of hearts within a 20.9 mm radius from the os. Histology showed small crevices and areas of very thin wall within the trabeculated appendage. CONCLUSIONS: The LAA orifice is oval shaped and thin areas of appendage wall and atrial wall are common. Potentially, the left superior pulmonary vein, mitral valve and anterior descending coronary artery can be at risk during occlusion of the os.

A prospective randomized clinical trial of patellar resurfacing and nonresurfacing in bilateral TKA.

UNLABELLED: We conducted a randomized clinical trial to determine long-term outcome differences of patella resurfacing versus nonresurfacing in patients undergoing bilateral total knee arthroplasty. We questioned whether there were differences with respect to the operative procedure, anterior knee pain, Knee Society scores, patellofemoral-related revision rates, patient satisfaction and preference, and patellofemoral functional activities. Thirty-two patients (64 knees) underwent primary bilateral single-stage total knee arthroplasty for osteoarthritis. All patients received the same cruciate-retaining total knee arthroplasty. Patients were randomized to resurfacing or nonresurfacing of the patella for the first total knee arthroplasty, and the second knee received the opposite treatment. All living patients were followed to a minimum of 10 years. We found no differences with regard to range of motion, Knee Society Clinical Rating Score, satisfaction, revision rates, or anterior knee pain. Thirty-seven percent of patients preferred the resurfaced knee, 22% the nonresurfaced knee, and 41% had no preference. Two patients (7.4%) in the nonresurfaced group and one patient (3.5%) in the resurfaced group underwent revision for a patellofemoral-related complication. Equivalent clinical results for resurfaced and nonresurfaced patellae in total knee arthroplasty were demonstrated in this 10-year randomized clinical trial. LEVEL OF EVIDENCE: Level I, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Spectrum of pathological changes in both ventricles of patients dying suddenly with arrhythmogenic right ventricular dysplasia. Relation of changes to age.

AIMS: To quantify the variation in fibrosis, fat and muscle within the walls of both ventricles and within the different regions of the heart from six patients dying suddenly of arrhythmogenic right ventricular dysplasia (ARVD) aged 20-60 years. METHODS: Seven heart regions were examined both macroscopically and histologically using the Picro-Sirius red stain. Quantification of fibrosis, fat and muscle was performed in each region and transmural layer using grid counting. RESULTS: There were macroscopic changes in all examined hearts. A higher percentage of fat with less fibrosis and muscle was observed within the right ventricle of the older patients. The left ventricle had more pathology in the older age group. Statistical differences in pathology in the heart were found. Fat predominated in the epicardial layer in the right and left ventricles of all patients, while the interventricular septum was the least affected. CONCLUSIONS: In ARVD, the pathology varies with age in both ventricles, fibrosis being the earliest hallmark of disease, with fatty infiltration evolving later. It should be labelled arrhythmogenic ventricular dysplasia because of biventricular involvement. Histopathologists should therefore sample from whole slices of the heart, so that all the changes can be observed.

Development of Z-scores for fetal cardiac dimensions from echocardiography.

OBJECTIVES: Z-scores for cardiac dimensions are well established in postnatal life, but have yet to be developed for fetal cardiac dimensions. These would be of real advantage to the clinician in accurately quantifying size and growth of cardiac dimensions and to the researcher by allowing mathematical comparison of growth in differing subgroups of a disease. The purpose of this observational study, conducted at tertiary fetal medicine and cardiology units, was to produce formulae and nomograms allowing computation of Z-scores for fetal cardiac dimensions from knowledge of femur length (FL), biparietal diameter (BPD) or gestational age (GA) using fetal echocardiography. METHODS: Seventeen fetal cardiac dimensions were measured in 130 pregnant women with singleton fetuses of gestational age 15-39 weeks. Regression equations were derived relating all dimensions to FL, BPD and GA. From the calculations, formulae were then developed allowing fetal cardiac Z-score computation. RESULTS: The relationships between cardiac dimensions and FL, BPD or GA were described following natural log transformation. From this analysis, FL (taken as an expression of fetal size) had the highest correlation to fetal cardiac dimensions. From the developed nomograms, Z-scores of specific fetal cardiac structures could be estimated from knowledge of the FL, BPD or GA and echocardiographically derived measurements. CONCLUSIONS: This study allowed computation of Z-scores in fetal life for 17 cardiac dimensions from FL, BPD or GA. Previous studies of normal data allowed qualitative assessment of where abnormal cardiac dimensions lay with regard to the normal range. Z-scores from this study allow quantitative analysis of where such dimensions lie relative to the mean. This permits exact assessment of growth of fetal cardiac structures in normal hearts and particularly in congenitally abnormal hearts where quantitative assessment of the growth of cardiac structures is important in analyzing and planning treatment strategies.

Molecular diagnosis of lymphomas and associated diseases.

The aim of this review is to explore some of the major ways in which the techniques of molecular biology are affecting individual patient diagnosis with respect to lymphoproliferative disorders. The main impact in this particular sphere has been through the polymerase chain reaction which has enabled clonal analysis, the detection of diagnostically and prognostically important chromosomal abnormalities and the monitoring of therapeutic intervention via the detection of residual disease. This allows increased diagnostic accuracy and enables better targeting of therapeutic intervention. A younger technology, but none the less one with great diagnostic potential, is that of fluorescence in situ hybridisation which has bridged the gap between conventional cytogenetics, with its reliance on living tissues and its relative insensitivity in picking up chromosomal abnormalities, and molecular biology which forsakes morphology and which, in the shape of PCR at least, deals with relatively minute segments of the genome. The main techniques of clonal analysis are compared and contrasted and the usefulness of the detection of some of the major chromosomal abnormalities is discussed. The place of fluorescence in situ hybridisation is also elaborated. The major advantages and disadvantages of each of these techniques are described and their place in the scheme of diagnosis and treatment is briefly elucidated.

The polymerase chain reaction in diagnosing lymphoid disorders.

The application of PCR to lymphoid diagnosis has come a long way in a few years. The technique brings the advantage of rapidity and (relative) ease of use, as well as being inexpensive. Whilst the range of chromosomal abnormalities thus detectable is at present small, the adaptation of PCR to the detection and monitoring of clones is becoming increasingly useful.

14;18 translocation in primary intestinal lymphoma: detection by polymerase chain reaction in routinely processed tissue.

Chromosomal translocations involving the heavy chain immunoglobulin locus on chromosome 14 and a region on chromosome 18 encoding the bcl-2 gene [t(14;18)] are a characteristic and prevalent chromosomal abnormality in nodal malignant lymphoma, particularly follicular lymphoma. Using the polymerase chain reaction on routinely processed tissue, t(14;18) has been demonstrated in 22% of primary intestinal lymphomas, i.e. in two of nine cases of malignant lymphomatous polyposis, in four of 19 cases of polymorphic B-cell lymphoma and in one of four high-grade unclassified tumours. The findings in this study contradict those of other studies which have shown no such translocation in primary gastric and small intestinal lymphoma. The presence of t(14;18) indicates heterogeneity of molecular abnormalities within histopathologically homogeneous tumours and suggests that caution should be employed in using molecular cytogenetic data to support theories of tumour histogenesis. The low prevalence of this translocation in intestinal lymphoma makes the use of such a methodology as a primary diagnostic aid doubtful, although the technique may help to distinguish primary and secondary lymphoma and could also be used to demonstrate secondary spread.

The rapid detection of clonal T-cell proliferations in patients with lymphoid disorders.

A series of T-cell proliferations in peripheral blood, bone marrow, or tissue samples were analyzed for clonality. The technique used employs the polymerase chain reaction to amplify portions of the rearranged T-cell receptor beta chain genes, using primers recognizing conserved sequences of the variable, diversity, and joining region segments. We examined 17 cases of T-cell lymphoma or leukemia; a clone was identified in 13 cases (76%) overall and in 7 of 8 cases (87.5%) in which both beta-chain alleles were known to be rearranged, as shown by restriction enzyme analysis. No clonal rearrangements were detected in samples from 13 non-T-cell disorders, including B-cell lymphomas, reactive lymphoid proliferations, and nonlymphoid tumors. This method is useful for detecting clones in thymic and post-thymic T-cell malignancies and has the advantages of being extremely rapid (a result is obtained within hours of the biopsy procedure), requiring no radiolabeling, using only a small amount of tissue, and being applicable to formalin-fixed, paraffin-embedded tissue.

The polymerase chain reaction in the diagnosis of early mycosis fungoides.

The earliest or patch stage of mycosis fungoides may present diagnostic difficulty both clinically and pathologically. The present study of the polymerase chain reaction (PCR) as a diagnostic tool in early mycosis fungoides was therefore undertaken, using a rapid PCR method for the detection of gamma- and beta-chain T-cell receptor (TCR) gene rearrangements in routine formalin-fixed, paraffin-embedded histological sections. Forty-two biopsies were studied from 26 patients with mycosis fungoides. Twenty-three skin biopsies with a clinicopathological diagnosis of early, or patch stage, mycosis fungoides were investigated. Of these, 18 (78 per cent) showed TCR-gamma or both beta- and gamma-chain TCR gene rearrangements. TCR gene rearrangements were shown in seven of the 14 plaque stage lesions (50 per cent) and also in the single case of tumour stage disease. Where gene rearrangements were identified, these were identical in all biopsies from an individual patient, irrespective of the site of the lesion, the disease stage, or the time lapse between the biopsies. The PCR is therefore a highly sensitive technique, which can be performed on routine pathological material, in cases where the diagnosis of early mycosis fungoides cannot be made with certainty on conventional histopathological and immunohistochemical grounds.

Frequent T and B cell oligoclones in histologically and immunophenotypically characterized angioimmunoblastic lymphadenopathy.

The identification of clonal rearrangements of T cell receptor (TCR) genes is central to the diagnosis of T cell lymphomas. However, in angioimmunoblastic lymphadenopathy (AILD), first described as a nonneoplastic proliferation associated with immunodeficiency, the heterogeneity of TCR and IgH gene rearrangements suggest that some cases may harbor multiple lymphoid clones. In this study we have isolated DNA from archival paraffin biopsy material from 22 cases of AILD identified on the basis of classical histological and immunohistochemical features with the aim of establishing the occurrence of clones and oligoclones, the frequency of TCR and immunoglobulin heavy chain (IgH) variable (v) gene use, and the relationship of these findings to the presence of Epstein-Barr virus. DNA extracted from the biopsies was amplified using the polymerase chain reaction (PCR) and sequenced to detect functional and nonfunctional gene rearrangements. Epstein-Barr virus-encoded short RNA species (EBERs) were detected using in situ hybridization combined with immunochemistry to identify the phenotype of the Epstein-Barr virus-infected cells. Fifty-seven clonal products were found in 20/22 patients: TCRgamma clonal products were identified in 16/22, TCRbeta clonal products in 16/22 and IgH clonal products in 6/22 cases. Oligoclonal PCR products were seen for TCR in 3/22 and for IgH in 3/22 cases. In one biopsy PCR products from all reactions were polyclonal. Sequence analysis revealed functional TCRgamma, TCRbeta, and IgH sequences in 6/12, 9/11, and 8/8 cases, respectively. Functional TCR and/or IgH oligoclones were detected in 6/20 (30%) cases. In addition, nonfunctional TCR and IgH sequences were found in 11 cases. EBERs were identified in 18/20 cases varying from occasional to 25 to 30% nuclei staining and were associated with both T and B cells, although the majority were of indeterminate phenotype. The presence of EBERs was not associated with all clonal IgH gene rearrangements but was associated with B cell oligoclones. Patterns of gene recombinations indicated that the majority of TCRgamma recombinations used GV1 and GJ1S3/2S3 genes. Six out of eleven cases used TCR BV4S1 or BV2S1 genes associated with various BJ and BD1/2 genes. No common IgH gene usage was identified, but 8 clones had varying degrees of replacement and silent mutations (0.6-10.1%), consistent with B cell clones having undergone somatic mutation in the germinal center, and 3 clones harbored unmutated V genes, consistent with naive B cells. Our data do not support the concept of AILD as a clearly defined peripheral T cell lymphoma (PTCL). Rather, they suggest that AILD as defined by histology and immunohistochemistry is either a heterogeneous entity or represents a lymphoproliferation associated with immunodeficiency in which clonal T cell or B cell proliferation may occur.

Expression of desmin and myoglobin in rhabdomyosarcomas and in developing skeletal muscle.

Immunohistochemical staining for desmin and myoglobin was investigated in 35 rhabdomyosarcomas from young people and in skeletal muscle from 16 human fetuses of known gestational age. Twenty-nine of the rhabdomyosarcomas expressed desmin but six undifferentiated or poorly-differentiated tumours were desmin negative. Of the desmin positive cases, most undifferentiated or poorly-differentiated sarcomas expressed desmin alone (12/35). Tumours with increasing rhabdomyoblastomic differentiation co-expressed myoglobin (9/35) and well-differentiated examples also contained cross-striations (7/35). Skeletal muscle from fetuses aged 8 weeks or less consisted mainly of primitive desmin negative round cells. As the cells began to differentiate they quickly expressed desmin and, at approximately 10 weeks, myoglobin was expressed and cross-striations were seen. The combined results strengthen the view that desmin (within a strictly defined context of round cell tumours in young people) is a reliable marker for rhabdomyoblastic differentiation. Support is also given to the notion that very primitive rhabdomyosarcomas may be desmin-negative, although the difficulties of establishing firm diagnoses for some of these tumours is emphasized.