Entitäten der Weichteilsarkome

Classification and Treatment of Diseases in the Age of Genome Medicine Based on Pathway Pathology

The focus of pathology as a biomedical discipline is the identification of the pathomechanisms of diseases and the integration of this knowledge into routine diagnosis and classification. Standard tools are macroscopic and microscopic analysis complemented by immunohistochemistry and molecular pathology. So far, classification has been based on the paradigm of cellular pathology established by Rudolf Virchow and others more than 150 years ago, stating that diseases originate from diseased cells. This dogma is meanwhile challenged by the fact that cells can be fully reprogrammed. Many diseases are nowadays considered to originate from undifferentiated stem cells, induced into a diseased state by genetic or epigenetic alterations. In addition, the completion of the Human Genome Project, with the identification of more than 20.000 genes and a much higher number of gene variants and mutations, led to the concept that diseases are dominated by genetics/epigenetics rather than cells of origin. The axiom of cellular pathology, however, still holds true, as cells are the smallest animate units from which diseases originate. Medical doctors and researchers nowadays have to deal with a tremendous amount of data. The International Classification of Diseases will expand from 14.400 entities/codes in ICD-10 to more than 55.000 in ICD-11. In addition, large datasets generated by “genomics“, e.g., whole-genome sequencing, expression profiling or methylome analysis, are meanwhile not only applied in research but also introduced into clinical settings. It constitutes a major task to incorporate all the data into routine medical work. Pathway pathology may help solve this problem. It is based on the realization that diseases are characterized by three essential components: (i) cells of origin/cellular context and (ii) the alteration of cellular as well as (iii) molecular/signal transduction pathways. The concept is illustrated by elaborating on two key cellular pathways, i.e., the cellular senescence of normal cells and the immortality of cancer cells, and by contrasting single cell/single pathway diseases, such as mycoplasma and coughing pneumonia, with complex diseases such as cancer, with multiple cell types as well as multiple affected cellular and signaling pathways. Importantly, the concept of pathway pathology is not just intended to classify disease, but also to conceive new treatment modalities. This article is dedicated to Dr. Leonard Hayflick, who made basic discoveries in pathway pathology not only by identifying cells causing disease (Mycoplasma pneumoniae) and establishing cell strains for treating disease (WI-38 for viral vaccines), but also by first describing cellular senescence and immortality.

Stem cell transcription factor SOX2 in synovial sarcoma and other soft tissue tumors

BACKGROUND

SOX2 has gained considerable interest as a pluripotency inducing gene. Co-transfection of SOX2 together with NANOG, KLF4 and c-MYC into adult fibroblasts was able to generate pluripotent stem cells. SOX2 has been reported to be expressed in synovial sarcoma, a tumor being characterized by the SS18-SSX gene fusion forming part of the SWI/SNF chromatin remodeling complex that affects histone methylation. The role of SOX2 in this tumor type as well as other soft tissue tumor entities however is still poorly characterized. We analyzed SOX2 protein expression in soft tissue tumors. Alongside we tested Histone H3 expression (H3K27me3) in SOX2 positive cases to investigate this epigenetic mark and its correlation with the SOX2 status and clinicopathological parameters.

METHODOLOGY

In total, 60 samples of synovial sarcomas from the reference center for soft tissue tumors at the institute of pathology of the Jena University hospital were included into the study along with 343 other tissue tumors. Protein analysis was done by immunohistochemistry of tissue microarrays. All synovial sarcoma cases were confirmed by molecular testing using SS18 FISH break apart probes.

RESULTS

SOX2 reactivity was detectable in 35 synovial sarcoma cases (58.3%) while 25 (41.7%) were negative. Only 13 cases of the other 343 soft tissue tumors, varying from nodular fasciitis to undifferentiated pleomorphic sarcoma, revealed a SOX2 expression, 12 out of these were undifferentiated high grade sarcoma. There was no obvious correlation with the clinicopathological data. H3K27me3 immunohistochemistry of the synovial sarcoma cases revealed a high statistically significant correlation between SOX2 and H3K27me3 expression (p < 0,0005, Chi square test). Similar to SOX2, there was no correlation between H3K27me3 expression and tumor grade. Six SOX2 positive synovial sarcoma cases were analyzed by FISH using a SOX2/CEN3 dual color FISH probe. None of these cases revealed an amplification of the SOX2 gene.

CONCLUSION

The data confirms previous studies reporting SOX2 and H3K27me3 expression in synovial sarcoma and reveals that both biomarkers are related to each other. It strengthens the notion that the tumor type is driven by epigenetic processes similar to those that are operating in pluripotent stem cells. The relevance of these parameters in the pathway pathology of synovial sarcoma, i.e. the timing and dosing of SOX2 and H3K27me3 expression initiated by the SS18-SSX driver mutation together with the interplay of these events with other signaling pathways, cellular mechanisms and additional mutations in tumor progression, will require further studies.