Electron microscopic evidence suggesting the myogenous derivation of the so-called alveolar soft part sarcoma

Abstract

Electron microscopic study has revealed distinctly different granules in cells comprising alveolar soft part sarcoma, carotid body tumor (nonchromaffin paraganglioma), malignant melanoma, and granular cell myoblastoma which allow for their differential diagnosis. This, as well as other pertinent information, militate against views that implicate a histogenetic relationship between alveolar soft part sarcoma and anatomical analogues of these alveolated neoplasms or those of neutral origin. On the other hand, the cytoplasmic crystalloids encountered in alveolar soft part sarcoma exhibit a striking morphological similarity to the rods observed in cells of benign rhabdomyoma and nemaline myopathy as well as Z‐band material and tropomyosin B. Differences noted between these structures, as well as rods observed in examples of alveolar or pleomorphic rhabdomyosarcoma, do not appear sufficiently significant to compromise the conclusion that the alveolar soft part sarcoma most likely represents a unique type of rhabdomyosarcoma.

Alveolar soft-part sarcoma: a review and update

“…10 12 23-25 The composition of these crystals was interpreted as a product similar to renin 24 or aggregates of actin filaments, 25 and it was suggested that they could be similar to the inclusions seen in rhabdomyoma or nemaline rod myopathy. 26 However, elegant recent work by Ladanyi et al, 27 including ultrastructural immunohistochemistry, has convincingly shown that the crystals consist of aggregates of the monocarboxylate transporter protein MCT1 and its cellular chaperone CD147. 27 …”

“…25 61 Similarly, the suggestion that ASPSs were malignant angioreninomas has been disproved by negative immunohistochemical studies for renin, as well as by the absence of clinical signs of hyperreninism in patients with ASPS. 25 Perhaps the longest lived hypothesis has been that ASPS is an unusual myogenous tumour, on the basis of some ultrastructural similarity of a component of the ASPS crystal to actin filaments, 25 overlap between the appearance of these crystals and those seen in nemaline myopathy and rhabdomyoma, 26 and variable expression of muscle-related proteins, such as actins and desmin. 28 However, as discussed in the section Immunohistochemical findings, the specificity and significance of these immunohistochemical findings have been questioned, and there is no convincing evidence of expression of truly muscle-specific proteins in ASPS.…”

Cytogenetic abnormalities of alveolar soft-part sarcomas using interphase fluorescent in situ hybridization: trisomy for chromosome 7 and monosomy for chromosomes 8 and 18 seem to be characteristic of the tumor

“…Rare sites, such as the uterus, the mediastinum, and bones have also been described [14,34,38]. The majority of the pathologists dealing with this tumor tried to present evidence for its myogenic origin [3,7,13,15,16,19,27,30,31,32,36]. Some other "lines of differentiations" (paraganglioma, granular cell myoblastoma, neural neoplasm, and angioreninoma) -although only transiently -have also been raised in the literature [9,23,32].…”

“…Numerous attempts have been made to define its tissue or cell origin. Ultrastructural analyses revealed the presence of the highly specific crystalloids, consisting of characteristically arranged actin filaments [3,13,31]. This fact raised the possibility of its muscle origin.…”

“…This fact raised the possibility of its muscle origin. However, some authors regarded the neoplasm as neurogenic [13,23,48]. The immunohistochemical analysis has also led to controversial results.…”