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Pleomorphic soft tissue myogenic sarcomas of adulthood. A reappraisal in the mid-1990s
W Schürch1, L R Bégin, T A Seemayer
1Department of Pathology, Hôtel-Dieu Hospital of Montrael, P.Q., Canada.
Abstract:
325 diverse sarcomas, 39 rhabdomyosarcomas (RMS), including all histologic variants, and 135 leiomyosarcomas (LMS) were identified. Within these two groups, 18 (46%) of the RMS and 14 (10%) of the LMS represented pleomorphic variants. These neoplasms were studied by morphology (histology and ultrastructure) and by immunohistochemical methods employing antibodies to intermediate filaments (vimentin and desmin) and actin isoforms [alpha-smooth (sm) and alpha-sarcomeric (sr) actins]. Twenty-four pleomorphic malignant fibrous histiocytomas (MFH) and eight pleomorphic liposarcomas (LS) were examined in a similar fashion. By light microscopy, the pleomorphic RMS, LMS, and MFH were indistinguishable, as each was dominated by pleomorphic cells disposed in a haphazard growth pattern; moreover, many featured fascicular, storiform, and sclerotic zones. The distinction between these neoplasms became apparent only following immunohistochemistry and/or ultrastructural study. All pleomorphic RMS disclosed rudimentary sarcomeres and exhibited the following cytoskeletal profile: vimentin (+) (18 of 18), desmin (+) (14 of 18), alpha-sr actin (+) (18 of 18) and alpha-sm actin (+) (five of 18). All the pleomorphic LMS featured smooth-muscle differentiation of variable degrees in the form of cytoplasmic bundles of microfilaments and associated dense bodies; their cytoskeletal profile was vimentin (+) (14 of 14), desmin (+) (seven of 14), alpha-sr actin (+) (none of 14), and alpha-sm actin (+) (eight of 14). The latter was demonstrated in all moderately differentiated, but absent or only focally expressed in poorly differentiated variants. All pleomorphic MFH and LS were devoid of myogenic (skeletal or smooth) ultrastructural features and expressed vimentin solely. This combined morphological and immunohistochemical study illustrates the following: First, these pleomorphic sarcomas are often indistinguishable by histologic growth pattern alone; thus, an accurate diagnosis requires study with all of these techniques. Second, pleomorphic myogenic sarcomas are restricted to adults and are not uncommon neoplasms among pleomorphic sarcomas: RMS (28%), LMS (21%), MFH (38%), and LS (13%). Third, the study defines desmin-negative and alpha-sm actin-positive pleomorphic RMS, and desmin-negative and alpha-sm-actin-negative pleomorphic LMS.
Insights
Diagnosing pleomorphic sarcomas like rhabdomyosarcomas (RMS) and leiomyosarcomas (LMS) requires advanced techniques, as histology alone is insufficient. Immunohistochemistry and ultrastructural studies are crucial for accurate classification of these challenging tumors.
Area of Science:
- Oncology
- Pathology
- Biochemistry
Background:
- Pleomorphic sarcomas, including rhabdomyosarcomas (RMS) and leiomyosarcomas (LMS), present diagnostic challenges due to overlapping histological features.
- Accurate differentiation is critical for appropriate patient management and treatment strategies.
Purpose of the Study:
- To investigate the utility of combined morphological (histology, ultrastructure) and immunohistochemical methods for distinguishing between pleomorphic RMS, LMS, malignant fibrous histiocytomas (MFH), and liposarcomas (LS).
- To characterize the cytoskeletal profiles of these pleomorphic sarcomas.
Main Methods:
- Histological and ultrastructural examination of 39 RMS, 135 LMS, 24 MFH, and 8 LS.
- Immunohistochemical analysis using antibodies against vimentin, desmin, alpha-smooth actin (α-sm actin), and alpha-sarcomeric actin (α-sr actin).
Main Results:
- Pleomorphic RMS, LMS, and MFH were histologically indistinguishable, showing pleomorphic cells in haphazard patterns.
- Immunohistochemistry revealed distinct cytoskeletal profiles: RMS showed vimentin(+), desmin(+), α-sr actin(+); LMS showed vimentin(+), variable desmin(+), α-sm actin(+); MFH and LS showed vimentin(+) only.
- Specific markers helped define desmin-negative/α-sm actin-positive RMS and desmin-negative/α-sm actin-negative LMS.
Conclusions:
- Histological assessment alone is inadequate for diagnosing pleomorphic sarcomas; a combination of techniques including immunohistochemistry is essential.
- Pleomorphic myogenic sarcomas (RMS and LMS) are primarily adult neoplasms and constitute a significant proportion of pleomorphic sarcomas.
- The study provides clear immunohistochemical criteria for differentiating these challenging sarcoma subtypes.