Common Diagnostic Challenges and Pitfalls in Genitourinary Organs, With Emphasis on Immunohistochemical and Molecular Updates

Small round cell sarcomas

Undifferentiated small round cell sarcomas (SRCSs) of bone and soft tissue comprise a heterogeneous group of highly aggressive tumours associated with a poor prognosis, especially in metastatic disease. SRCS entities mainly occur in the third decade of life and can exhibit striking disparities regarding preferentially affected sex and tumour localization. SRCSs comprise new entities defined by specific genetic abnormalities, namely EWSR1-non-ETS fusions, CIC-rearrangements or BCOR genetic alterations, as well as EWSR1-ETS fusions in the prototypic SRCS Ewing sarcoma. These gene fusions mainly encode aberrant oncogenic transcription factors that massively rewire the transcriptome and epigenome of the as yet unknown cell or cells of origin. Additional mutations or copy number variants are rare at diagnosis and, depending on the tumour entity, may involve TP53, CDKN2A and others. Histologically, these lesions consist of small round cells expressing variable levels of CD99 and specific marker proteins, including cyclin B3, ETV4, WT1, NKX3-1 and aggrecan, depending on the entity. Besides locoregional treatment that should follow standard protocols for sarcoma management, (neo)adjuvant treatment is as yet ill-defined but generally follows that of Ewing sarcoma and is associated with adverse effects that might compromise quality of life. Emerging studies on the molecular mechanisms of SRCSs and the development of genetically engineered animal models hold promise for improvements in early detection, disease monitoring, treatment-related toxicity, overall survival and quality of life.

The Challenges and Opportunities of Translational Pathology

Translational pathology has not caught up with the quality and quantity of translational medicine. Thus, challenges and opportunities related to translational pathology are discussed here. Pathologists should actively participate in reverse translational research that seeks mechanistic insights to explain clinical findings and/or solve clinical problems. Challenges in translational pathology include ambiguity in defining translational pathology, pathologists' mindsets about translational research, lack of sufficient workforce and immature publication outlets. However, with collective wisdom and support of various stakeholders, we can expand the pool of pathologist scientists, build a translational pathology community and drive innovations in medicine through computational, molecular genetic/genomic and digital pathology approaches.