[Rhabdomyosarcomas: structural distribution and analysis of an immunohistochemical profile].

Unlabelled: Rhabdomyosarcoma (RMS) is a malignant soft tissue tumor originating from primitive mesenchymal cells, which is most common in children.

Objective: To qualitatively and quantitatively assess the expression of myogenic transcription factors on a large sample, to identify potential phenotypic differences, and to estimate the distribution and frequency of aberrant markers, such as ALK, PAX5, WT1, PCK, CAM5.2, SIX1, and Synaptophysin.

Material And Methods: The investigation included 202 tumor tissue samples. Five tissue microarrays were assembled from the obtained material for subsequent histological and immunohistochemical studies.

Results: Embryonal RMS (ERMS) was diagnosed in 103 cases; alveolar RMS (ARMS) was detected in 80; spindle-cell/sclerosing RMS (SRMS) was found in 16 cases; epithelioid RMS (EpiRMS) was diagnosed in 2 patients. The expression of Myogenin and MyoD1 was detected in all the examined RMS tissue samples. ARMS was more characterized by staining at 1+ and 2+ intensities; at the same time, more than 50% of ERMS, SRMS, and EpiRMS cases showed staining at 1+ intensity. ALK expression was investigated using the D5F3 and p80 clones. The D5F3 clone displayed a higher staining intensity than the p80 clone (<0.05). The expression of PAX5 was observed in 13 of 75 ARMS cases. That of WT1 and SIX1 was found in all RMS groups.

Conclusion: The morphological diagnosis of RMS requires a careful assessment of all of the above factors, especially taking into account the variability in the expression of myogenic transcription factors and the high level of phenotypic aberration.