Different Characteristics of Mitochondrial Microsatellite Instability Between Uterine Leiomyomas and Leiomyosarcomas

Uterine leiomyomas are benign tumors of the uterus that arise clonally from smooth muscle cells of the myometrium and are the most common reason for hysterectomies. The aim of this study was to evaluate mitochondrial microsatellite instability (mtMSI) in uterine leiomyomas and leiomyosarcomas to clarify the molecular pathogenetic distinction between these tumors. DNA was isolated from paired normal and tumoral tissues in 50 patients with uterine leiomyomas and 14 patients with leiomyosarcomas. mtMSI was analyzed by using eight microsatellite markers. Our result showed that mitochondrial microsatellite instability was not found in all uterine leiomyomas. However, 3 (21.4%) of 14 patients with leiomyosarcomas had mtMSI and the frequencies of mtMSI in these tumors were significantly different (p < 0.01). Distinctive characteristics of mitochondrial genetic instability in uterine leiomyomas and leiomyosarcomas suggested the potential of mtMSI as a marker for differential diagnosis between them.     

Chromosome aberrations in uterine smooth muscle tumors: potential diagnostic relevance of cytogenetic instability

Cytogenetic studies were carried out on a low-grade metastatic uterine leiomyosarcoma and on a large degenerating uterine leiomyoma. The leiomyosarcoma and leiomyoma were hyperdiploid and hypodiploid, respectively, and both tumors contained multiple consistent chromosome aberrations. In the patient with leiomyosarcoma, flow cytometric studies of proliferative foci from a previously resected uterine leiomyoma revealed near triploidy, suggesting that the leiomyosarcoma was metastatic from an unrecognized malignant uterine primary lesion. The leiomyosarcoma was characterized by extreme cytogenetic instability, whereas the leiomyoma demonstrated cytogenetic stability. The present cases and review of the literature on leiomyosarcomas and leiomyomas reveal cytogenetic instability to be very common in leiomyosarcomas (present in 8 of 10 cases) and uncommon in leiomyomas (present in 1 of 25 cases). A grading system is described which might be useful in evaluating the diagnostic and prognostic relevance of cytogenetic instability in uterine, and other, malignancies.     

应用比较基因组杂交技术研究外阴鳞癌组织的遗传变异

背景与目的:外阴鳞状细胞癌约占女性外阴恶性肿瘤的80%～90%.但有关其遗传学研究却不多,本研究采用比较基因组杂交(comparative genomichybridization,CGH)技术分析外阴鳞癌组织的遗传变异,了解其遗传改变的特征.以期发现外阴鳞癌相关基因.方法:应用CGH技术检测21例外阴鳞癌基因组的不平衡性即其DNA的扩增或丢失.结果:外阴鳞癌常见的扩增染色体是3q,8q,12q.常见的丢失染色体是4p和3p.结论:外阴鳞癌细胞中存在多条染色体拷贝数的改变,由此引起相应癌基因的扩增和抑癌基因的丢失可能参与了外阴鳞癌的发生、发展.     

Activity of glycolytic enzymes and glucose-6-phosphate dehydrogenase in smooth muscle proliferation

The specific activity of hexokinase, phosphofructokinase, aldolase, enolase, pyruvate kinase and glucose-6-phosphate dehydrogenase was measured in 41 smooth muscle cell tumors: 20 leiomyomas and 21 cases of leiomyosarcoma. Statistical analysis revealed no significant differences in specific activity between normal smooth muscle tissue and the benign and malignant tumors originating from it. Quantification of the isozyme composition of pyruvate kinase showed a significant shift in isozyme pattern towards K-type subunits in leiomyosarcomas as compared to leiomyomas.     

DNA计量图像分析诊断子宫平滑肌肿瘤的特异性及标准化检测

应用电子计算机辅助ＤＮＡ影像计量分析仪（ＣＭ１ＤＮＡＣｙｔｏｍｅｔｅｔ．ＨＵＮＤ，Ｗｅｔｚｌａｒ，Ｇｅｒｍａｎｙ）测量３０例人正常子宫平滑肌、内膜上皮、纤维及淋巴细胞核ＤＮＡＩＯＤ值，以确定子宫组织特异性正常二倍体参照细胞及其校正因子。测量８０例子宫平滑肌瘤细胞核ＤＮＡ含量，发现各ＤＮＡ计量结果与正常平滑肌近似，无１例出现干系ＤＮＡ非整倍体和＞９ｃＥＥ，有４例出现＞５ｃＥＥ。测量３２例生长活跃的子宫平滑肌瘤，１８例检出干系ＤＮＡ非整倍体，１例检出＞９ｃＥＥ，１１例检出＞５ｃＥＥ，测量２７例子宫平滑肌肉瘤，２２例出现干系ＤＮＡ非整倍体，５例出现＞９ｃＥＥ，１８例出现＞５ｃＥＥ。本文结果表明，用于系ＤＮＡ非整倍体和＞９ｃＥＥ作为指标诊断子宫平滑肌瘤的特异性均为１００％，诊断子宫平滑肌肉瘤的敏感性分别为８１％和１９％，对生长活跃的子宫平滑肌瘤恶性性质的预测具有重要意义。＞５ｃＥＥ这一指标阈值不适合用于对子宫平滑肌肿瘤良、恶性质的判断。     

Comparative genetic patterns of glioblastoma multiforme: potential diagnostic tool for tumor classification

Cytogenetic and molecular genetic studies of glioblastoma multiforme (GBM) have shown that the most frequent alterations are gains of chromosome 7, losses of 9p loci and chromosome 10, and gene amplification, primarily of the epidermal growth factor receptor (EGFR) gene. Although this profile is potentially useful in distinguishing GBM from other tumor types, the techniques used tend to be labor intensive, and some can detect only gains or losses of genetic loci. Comparative genomic hybridization (CGH) is a powerful technique capable of identifying both gains and losses of DNA sequences. The present study compares the CGH evaluation of 22 GBM with classic cytogenetics, loss of heterozygosity by allelotyping, and gene amplification by Southern blot analysis to determine the reliability of CGH in the genetic characterization of GBM. The CGH and karyotypic data were consistent in showing gain of chromosome 7 accompanied by a loss of chromosome 10 as the most frequent abnormality, followed by a loss of 9p in 17 of 22 GBM cases. Loss of heterozygosity of chromosomes 10 (19/22) and 9p (9/22) loci confirmed the underrepresentation by CGH. Genomic amplifications were observed by CGH in 5 of the 10 cases where gene amplification was detected by Southern blot analysis. The data show that CGH is equally reliable, compared with the more established genetic methods, for recognizing the prominent genetic alterations associated with GBM and support its use as a plausible adjunct to glioma classification.     

Molecular cytogenetic characterization shows higher genetic homogeneity in conventional renal cell carcinoma compared to other kidney cancers

In this study seven primary kidney tumors out of 13 were cytogenetically characterized by comparative genomic hybridization (CGH) on the surgical specimens as well as by spectral karyotyping (SKY) analysis after short-term culturing. In two of the seven cases only a normal karyotype was identified. Non-clonal aberrations were observed in four of the seven cases. Overall numerical alterations were more frequent than structural changes. The two structural alterations identified constituted of a deletion of the short arm of chromosome 3 in a conventional renal cell carcinoma (RCC), and a ring chromosome derived from chromosome 8 in a papillary RCC. By CGH gains of copy number were revealed on chromosomes 3, 5, 7, 8q, and 20, while the losses encompassed 3p and 17p. In the papillary RCCs only gains were found. Comparison between SKY and CGH data suggests that the conventional RCCs are genetically more homogeneous than the other types of kidney cancer. In the two papillary RCCs, trisomies of chromosomes 7 and 17 were typical findings. In the transitional cell carcinoma different findings by CGH and SKY would suggest that these tumors constitute a heterogeneous population of tumor cells which could represent different steps of somatic evolution of tumors.     

Chromosomal abnormalities in glioblastoma multiforme tumors and glioma cell lines detected by comparative genomic hybridization

Comparative genomic hybridization (CGH) is a recent molecular cytogenetic method that detects and localizes gains or losses in DNA copy number across the entire tumor genome. We used CGH to examine 9 glioma cell lines and 20 primary and 10 recurrent glioblastoma tumors. More than 25% of the primary tumors had gains on chromosome 7; they also had frequent losses on 9p, 10, 13 and Y. The losses on chromosome 13 included several interstitial deletions, with a common area of loss at 13q21. The recurrent tumors not only had gains on chromosome 7 and losses on 9p, 10, 13 and Y but also frequent losses on 6 and 14. One recurrent tumor had a deletion of 10q22-26. Cell lines showed gains of 5p, 7 and Xp; frequent amplifications at 8q22-24.2, 7q2l-32 and 3q26.2-29 and frequent losses on 4, 10, 13, 14 and Y. Because primary and recurrent tumors and cell lines showed abnormalities of DNA copy number on chromosomes 7, 10, 13 and Y, these regions may play a fundamental role in tumor initiation and/or progression. The propensity for losses on chromosomes 6 and 14 to occur in recurrent tumors suggests that these aberrations play a role in tumor recurrence, the development of resistance to therapy or both. Analysis of common areas of loss and gain in these tumors and cell lines provides a basis for future attempts to more finely map these genetic changes.     

Molecular Cytogenetic Characterization in Four Pediatric Pheochromocytomas and Paragangliomas

Pheochromocytomas (PCCs) are rare tumors among children and adolescents and therefore are not genetically well characterized. The most frequently observed chromosomal changes in PCC are losses of 1p, 3q and/or 3p, 6q, 17p, 11q, 22q, and gains of 9q and 17q. Aberrations involving chromosome 11 are more common in malignant tumors. Unfortunately information about gene aberrations in childhood PCC’s is limited. We used comparative genomic hybridization (CGH) and array comparative genomic hybridization (aCGH) to screen for copy number changes in four children suffering from pheochromocytoma or paraganglioma. Patients were diagnosed at the age 13 or 14 years. Bilateral pheochromocytoma was associated with von Hippel-Lindau syndrome (VHL). Multiple paraganglioma was associated with a germline mutation in SDHB. We found very good concordance between the results of CGH and aCGH techniques. Losses were observed more frequently than gains. All cases had a loss of chromosome 11 or 11p. Other aberrations were loss of chromosome 3 and 11 in sporadic pheochromocytoma, and loss of 3p and 11p in pheochromocytoma, which carried the VHL mutation. The deletion of chromosome 1p and other changes were observed in paragangliomas. We conclude that both array CGH and CGH analysis identified similar chromosomal regions involved in tumorigenesis of pheochromocytoma and paragangliomas, but we found 3 discrepancies between the methods. We didn’t find any, of the proposed, molecular markers of malignancy in our benign cases and therefore we speculate that molecular cytogenetic examination may be helpful in separating benign and malignant forms in the future.     

Intratumoral genetic heterogeneity in pilocytic astrocytomas revealed by CGH-analysis of microdissected tumor cells and FISH on tumor tissue sections

Pilocytic astrocytomas are the most frequent gliomas of childhood. The majority of cases show cytogenetic normal karyotypes. Although in diffuse gliomas TP53 gene mutations or deletions occur with significant frequency, the role in pilocytic astrocytomas remains unclear. Histomorphologically different areas of 14 pilocytic astrocytomas were microdissected and analyzed for genetic aberrations and heterogeneity. CGH analysis revealed gains of chromosome arm 4q and 6q mainly in areas of classic biphasic pattern, whereas pleomorphic areas presented gains of chromosome 6 and 8q. Using two-color fluorescence in situ hybridization (FISH) the spatial distribution of aneuploidies for chromosomes 7, 8, 17 and the TP53 gene were assessed on parallel sections. FISH analysis revealed a significant percentage of cells with interspersed heterozygous deletions of TP53 in all tumors (14/14), ten cases showed also monosomy 17. Besides gains of chromosomes 7 and 8, losses of these chromosomes were detected in the majority of tumors. In conclusion, pilocytic astrocytomas show a genetic heterogeneity associated with variations of histologic structure as well as an intratumoral heterogeneity observed on single cell level by FISH.     

Recurrent allelic deletions at mouse chromosomes 4 and 14 in Myc-induced liver tumors

Transgenic mice expressing the c-Myc oncogene driven by woodchuck hepatitis virus (WHV) regulatory sequences develop hepatocellular carcinoma with a high frequency. To investigate genetic lesions that cooperate with Myc in liver carcinogenesis, we conducted a genome-wide scan for loss of heterozygosity (LOH) and mutational analysis of beta-catenin in 37 hepatocellular adenomas and carcinomas from C57BL/6 x castaneus F1 transgenic mice. In a subset of these tumors, chromosome imbalances were examined by comparative genomic hybridization (CGH). Allelotyping with 99 microsatellite markers spanning all autosomes revealed allelic imbalances at one or more chromosomes in 83.8% of cases. The overall fractional allelic loss was rather low, with a mean index of 0.066. However, significant LOH rates involved chromosomes 4 (21.6% of tumors), 14, 9 and 1 (11 to 16%). Interstitial LOH on chromosome 4 was mapped at band C4-C7 that contains the INK4a/ARF and INK4b loci, and on chromosome 14 at band B-D including the RB locus. In man, the homologous chromosomal regions 9p21, 13q14 and 8p21-23 are frequently deleted in liver cancer. LOH at chromosomes 1 and 14, and beta-catenin mutations (12.5% of cases) were seen only in HCCs. All tumors examined were found to be aneuploid. CGH analysis of 10 representative cases revealed recurrent gains at chromosomes 16 and 19, but losses or deletions involving mostly chromosomes 4 and 14 generally prevailed over gains. Thus, Myc activation in the liver might select for inactivation of tumor suppressor genes on regions of chromosomes 4 and 14 in a context of low genomic instability. Myc transgenic mice provide a useful model for better defining crosstalks between oncogene and tumor suppressor pathways in liver tumorigenesis.     

DIAGNOSTIC IMPLICATIONS OF IMMUNOHISTOCHEMICAL MARKERS IN UTERINE SMOOTH MUSCLE TUMORS

Objective: To evaluate the diagnostic implications of immunohistochemieal markers in uterine smooth muscle tumors. Methods: Formalin-fixed paraffin-embedded tissue blocks were selected from 17 uterine leiomyosarcomas, 40 uterine unusual leiomyomas and 25 uterine usual leiomyomas. Utilizing immunohistochemical techniques with antigen retrieval, serial sections of each tumor for immunoreactivity with myogenic markers, ovarian steroid receptors, CD44v3, proliferating cell nuclear antigen and mast cells were assessed. Results: Although the myogenic markers and CD44v3 showed less frequent positivity in uterine leiomyosarcomas than those in unusual leiomyomas,they were not reliable markers for differentiating leiomyosarcoma from leiomyoma. Uterine leiomyosarcoma tended to have lower ovarian steroid receptors immunoreactivity rates than leiomyoma. Leiomyoma tended to have a higher quantity of intratumoral mast cells than leiomyosarcoma, while the expression of proliferating cell nuclear antigen was lower in them. Conclusion: Because the estimation of mitotic count was subject to significant variation, the immunohistochemical expression of ovarian steroid receptors, mast cells and proliferating cell nuclear antigen seemed to be helpful for the discrimination of unusual leiomyoma from leiomyosarcoma.     

Genetic characterization of lung metastases in renal cell carcinoma

Prognosis of patients with renal cell carcinoma (RCC) is mainly determined by metastases. The understanding of the metastatic process will give the basis for a differential diagnosis leading to an individual prognosis and to new therapeutical strategies. In order to define specific genetic alterations which are common in renal cancer metastases of the lung, we performed comparative genomic hybridization (CGH) on metastases and in some cases on their related primary renal tumors. For CGH, DNA was isolated from 2 or 5 paraffin sections (5 micro m). Tumor and normal (control) DNAs were amplified by DOP-PCR and labeled with biotin-dUTP and digoxigenin-dUTP, respectively. Hybridization and detection were carried out according to standard protocols. In 33 out of 40 metastases, genetic alterations were detected, most frequently these were losses of chromosomes 3p (74%), 8p (31%), 9 or 9q (34%), 14 [26%, 18q (40%) and gains of chromosome 5/5q 34%], 7 (31%) and 12 (26%). Combination of loss of 8p and gain of 8q occurred frequently. The mean number of aberrations per tumor was 8.1 (1-11). The comparison of alterations in related primary and metastatic tumors showed identical alterations in 5 out of 8 cases. This study demonstrates, that lung metastases from renal cell carcinoma are characterized by an accumulation of specific genetic alterations which show a clonal relationship to the related primary tumors.     

Chromosomal aberrations in sporadic pituitary tumors

Pituitary adenomas are common intracranial neoplasms that may be hormone-secreting or nonfunctional. Genetic defects associated with some pituitary tumors have been identified, although our understanding of the underlying molecular mechanisms remains incomplete. We have studied 75 sporadic pituitary tumors, representing the major clinical subtypes, by comparative genomic hybridization (CGH) with the aim of assessing for DNA copy number changes. CGH revealed chromosomal imbalances in 34 adenomas (45.3%), whereby gains were 4.9 times more frequently observed than losses. Most of the genetic alterations detected by CGH affected entire chromosomes (108/131, 82.4%). Gain of genetic material was observed predominantly on chromosomes X (24/75, 32%), 19 (12/75, 16%), 12 (6/75, 6.7%), 7 and 9 (5/75, 6.7%), whereas loss of DNA sequences most frequently affected chromosomes 11 (4/75, 5.3%), 13 and 10 (3/75, 4%). There were no significant differences in the CGH results for the individual clinical subtypes of pituitary tumors. These results reveal a nonrandom pattern of chromosomal alterations in pituitary tumors, in particular gains of entire chromosomes, and this may contribute to the development of such neoplasms.     

Array comparative genomic hybridization reveals distinct DNA copy number differences between gastrointestinal stromal tumors and leiomyosarcomas

Leiomyosarcomas are spindle cell tumors showing smooth muscle differentiation. Until recently, most gastrointestinal stromal tumors (GIST) were also classified as smooth muscle tumors, but now GISTs are recognized as a separate entity, defined as spindle cell and/or epithelioid tumors localized in the gastrointestinal tract. Using microarray-based comparative genomic hybridization (array CGH), we have created a detailed map of DNA copy number changes for 7 GISTs and 12 leiomyosarcomas. Considerable gains and losses of chromosomal segments were observed in both tumor types. The most frequent aberration observed in GISTs was loss of chromosomes 14 and 22, with minimal recurrent regions in 14q11.2-q32.33 (71% of the tumors) and 22q12.2-q13.31 (100%). In leiomyosarcomas, frequent loss of chromosome 10 and 13q was observed, with minimal recurrent regions in 10q21.3 (75%) and 13q14.2-q14.3 (75%). Recurrent high-level amplification of 17p13.1-p11.2 was detected in leiomyosarcomas. Expression profiling using cDNA microarrays revealed four candidate genes in this region with high expression (AURKB, SREBF1, MFAP4, and FLJ10847). Altered expression of AURKB and SREBF1 has been observed previously in other malignancies. Hierarchical clustering of all samples separated GISTs and leiomyosarcomas into two distinct clusters. Statistical analysis identified six chromosomal regions, 1p36.11-p13.1, 9q21.11-9q34.3, 14q11.2-q23.2, 14q31.3-q32.33, 15q24.3-q26.3, and 22q11.21-q13.31, which were significantly different in copy number between GISTs and leiomyosarcomas. Our results show the potential of using array comparative genomic hybridization to classify histologically similar tumors such as GISTs and leiomyosarcomas.     

Chromosomal aberrations and genetic relations in benign, borderline and malignant phyllodes tumors of the breast: a comparative genomic hybridization study

Phyllodes tumors are not quite rare fibroepithelial neoplasms of the breast that show a broad spectrum of clinical behaviour. The molecular genetic features of the heterogenous groups of neoplasms have not been studied in detail yet. We have used comparative genomic hybridization to analyze chromosomal copy number changes in 36 cases of phyllodes tumors (including benign, borderline and malignant phyllodes tumors, 12 cases each). The average number of chromosome copy changes (range) in benign, borderline and malignant phyllodes tumors were 5.58 (0–20), 14.08 (3–23), and 12.42 (0–29) respectively. In benign phyllodes tumors the number of gains and losses was in balance (2.50 vs 3.08), while in borderline and malignant phyllodes tumors gains occurred more often than losses (9.25 vs 4.83, 9.5 vs 2.92). The result suggests the molecular cytogenetics of borderline and malignant phyllodes tumors is similar, and the most striking difference with benign phyllodes tumors is an increased number of chromosomal gains in a nonrandom distribution. Gains of 4q12 seem especially to be involved in the progression of benign to borderline and malignant phyllodes tumors, possibly because of overexpression of oncogenes at these loci.     

Patterns of chromosomal imbalances in invasive breast cancer

Invasive breast carcinomas are characterized by a complex pattern of chromosomal alterations. We applied comparative genomic hybridization (CGH) to analyze 105 primary breast carcinomas using histograms to indicate the incidence of DNA imbalances of tumor subgroups and difference histograms to compare invasive ductal carcinomas (IDC) with lobular carcinomas (ILC), well and poorly differentiated carcinomas (G1/G3) and estrogen receptor-positive and -negative tumors (ER(+)/ER(-)). Only single imbalances showed a higher incidence in ILC compared with IDC, i.e., gains on chromosomes 4 and 5q13-q23 as well as deletions on chromosomes 6q, 11q14-qter, 12p12-pter, 16q, 17p, 18q, 19, and 22q. Of these, particularly gains of 4 and losses at 16q21-q23, and 18q12-q21 were statistically significant. For most loci, IDC showed more alterations providing a genetic correlate to the fact that ductal carcinoma overall is associated with a worse prognosis than ILC. Of these, many imbalances showing statistical significance were also observed in G3 and ER(-) tumors, i.e., deletions at 2q35-q37, 3p12-p14, 4p15-p16, 5q, 7p15, 8p22-p23, 10q, 11p, 14q21-q31, 15q, and gains at 2p, 3q21-qter, 6p, 8q21-qter, 10p, 18p11-q11, and 20q, suggesting that they contribute to a more aggressive tumor phenotype. By contrast, gains on chromosome 5q13-q23 as well as deletions at 6q, 16q and 22q were more prevalent in G1 and ER(+) tumors. The ratio profiles of all cases as well as histograms are accessible at our CGH online tumor database at http://amba.charite.de/cgh. Our results highlight distinct chromosomal subregions for cancer-associated genes. In addition, these imbalances may serve as markers for a genetic classification of invasive breast cancer.     

High level amplification of 1p32-33 and 2p22-24 in small cell lung carcinomas

Small cell lung cancer (SCLC) is a frequently occurring, highly aggressive tumor with a generally poor clinical outcome. In order to approach the genetic mechanisms behind the tumor progression, a general screen for DNA copy number alterations was performed using comparative genomic hybridization (CGH). In the series of 23 cases analyzed, CGH alterations were frequently detected ranging from 9 to 22 abnormalities in the individual tumors. The most frequent losses were detected on chromosome arms 3p (23/23), 13q14-21 (23/23), 4p (20/23), 4q (20/23), and 2q22-24 (18/23), while gains preferentially involved chromosome arms 19p (18/23), 19q (17/23), 1p31-35 (15/23), 17q22-25 (11/23), and 5p14-15.3 (9/23). In addition, high level amplification at chromosome arms 1p32-33 and 2p22-24 were found in three and two cases, respectively. Candidate genes for these amplifications include the l-MYC (1p32) and n-MYC (2p24.1) oncogenes, which have been previously found to be overexpressed in SCLC. Taken together, the findings demonstrate a high level of chromosomal instability in SCLC, which is well in agreement with the highly malignant phenotype of this tumor type. Subchromosomal regions involved in gains and losses were delineated and the amplifications of 1p32-33 and 2p22-24 were demonstrated, thus providing starting points for the exact characterization of molecular events involved in SCLC tumor progression.     

Smooth muscle tumors of the gastrointestinal tract. A study of 56 cases followed for a minimum of 10 years

Cases of gastrointestinal smooth muscle tumor seen at M. D. Anderson Hospital and followed for a minimum of 10 years are presented. The tumors were classified as high-grade leiomyosarcoma (41 cases), low-grade leiomyosarcoma (13 cases), and leiomyoma (2 cases). All of the leiomyosarcomas originated in the stomach (21 cases), small intestine (29 cases), or rectum (4 cases) and appeared to have arisen from the muscularis propria. Leiomyosarcomas were considered high-grade when the maximal mitotic rate in ten consecutive high-power fields was ten or more and low-grade when this rate was lower (actual maximal rates in the low-grade group varied from 1-5/10 high-power fields). All patients with high-grade leiomyosarcoma died of tumor after intervals ranging from 5 to 90 months (median, 25 months). All but two with low-grade leiomyosarcoma also died of tumor, but frequently after much longer intervals (range, 42-221 months; median, 98 months; survival difference P = 0.002). Intervals to recurrence and metastasis were correspondingly longer in the low-grade group (up to 188 months). The two leiomyomas were small (less than 2 cm), had no mitotic figures, and were less cellular than any of the leiomyosarcomas. However, they both occurred in locations in which no leiomyosarcomas were seen (muscularis propria of the esophagus and muscularis mucosae of the rectum); therefore, the problem of distinguishing leiomyomas from leiomyosarcomas in sites where the latter did arise could not be resolved, particularly in view of the fact that fatal low-grade leiomyosarcomas had diameters as small as 1 cm and maximal mitotic rates as low as one per ten high-power fields. "Leiomyoblastoma" was not found to be an entity; it is recommended that this term be dropped.