To the Editor.-I would like to point out an interpretational error in a recent article on epithelioid leiomyosarcoma of the deep soft tissues.1 The authors describe the tumor as containing "thin microfilaments," and the reader is referred to Figure 3. This term is generally used to mean the actin filaments or myofilaments typical of smooth muscle cell differentiation. Abundant filaments are indeed illustrated in Figure 3, but these are unambiguously of intermediate filament type. Given the immunostaining results in this case (including desmin negativity), they are probably composed of vimentin.
This point is important for 2 reasons. First, the misinterpretation gives a false perception of the nature of this tumor. Well-differentiated leiomyosarcomas can be expected to have all or most of the organelles and marker proteins characteristic of smooth muscle differentiation, including abundant cytoplasmic myofilaments (actin filaments) with focal densities. In line with decreasing levels of differentiation, these features tend to be lost. At the cellular level, therefore, the tumor in question is a poorly differentiated leiomyosarcoma. The diagnosis rests significantly on immunostaining for alpha-smooth muscle actin, and the tumor has no demonstrated ultrastructural features of smooth muscle differentiation, contrary to the authors' view ("some [tumor] cells exhibited ultrastructural evidence of true smooth muscle differentiation"). In its cellular differentiation, this tumor would be similar to those epithelioid gastrointestinal tumors referred to in the past as leiomyoblastoma,2 showing no or very little smooth muscle ultrastructure.
Second, the misinterpretation is a disservice to electron microscopy, whose value as a technique giving information on phenotype continues to be documented.3-7 Successful use of the technique, however, depends on appropriate levels of interpretational expertise.
BRIAN EYDEN, PhD
Department of Histopathology
Christie Hospital NHS Trust
Manchester M20 4BX
In Reply.-I thank Dr Eyden for his astute review of our article, "Epithelioid Leiomyosarcoma of the External Deep Soft Tissue,"1 and for sharing his expertise in the interpretation of the filament type in Figure 3. I have reviewed the article, including Figure 3 and all electron micrographs in the case, and concur with his opinion that this is a poor demonstration of actin-type filaments, and in fact, more likely represents intermediatetype filaments.
As mentioned by Dr Eyden and in our "Comment" section, our diagnosis of leiomyosarcoma also rests on positive immunoreactivity for alphasmooth muscle actin and ot-sarcomeric actin (Figure). As described in the "Comment" section of the article, metastatic gastrointestinal stromal tumor was excluded by negative immunoreactivity for c-Kit protein and CD34, as well as by clinical findings.
I am sure that further work into the value of electron microscopy and the interpretation of its results will continue to confirm its importance and accuracy as a technique for giving information on phenotype.
TETSUJI YAMAMOTO, MD
Department of Orthopaedic Surgery
Kobe University School of Medicine
Kobe 650-0017, Japan
1. Yamamoto T, Minami R, Ohbayashi C, Inaba M. Epithelioid leiomyosarcoma of the external deep soft tissue. Arch Pathol Lab Med. 2002;126:468470.
2. Miettinen M, Lasota J. Gastrointestinal stromal tumors: definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch. 2001;438:1-12.
3. Kandel R, Bedard Y, Fan Q-H.Value of electron microscopy and immunohistochemistry in the diagnosis of soft tissue tumors. Ultrastruct Pathol. 1998;22:141-146.
4. Mierau G. Electron microscopy for tumour diagnosis: not redundant-resurgent! [part of "Expert Opinion" feature: "Electron Microscopy for Tumour Diagnosis: Is It Redundant?"l. Histopathology. 1999; 35:99-102.
5. Eyden B. Electron microscopy in tumour diagnosis: continuing to complement other diagnostic techniques [part of "Expert Opinion" feature: "Electron Microscopy for Tumour Diagnosis: Is It Redundant?"]. Histopathology. 1999;35:102-108.
6. Lloreta Trull J, Ferrer L, Ribalta T, et al. Electron microscopy in pathology articles: a retrospective appraisal. Ultrastruct Pathol. 2000;24:105-108.
7. Tucker JA. The continuing value of electron microscopy in surgical pathology. Ultrastruct Pathol. 2000;24:383-389.
1. Yamamoto T, Minami R, Ohbayashi C, Inaba M. Epitheloid leiomyosarcoma of the external deep soft tissue. Arch Pathol Lab Med. 2002; 126:468470.
Copyright College of American Pathologists Apr 2003
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