L'hybridation in situ en fluorescence (FISH) utilisant le kit multisonde UroVysion® dans les cytologies urinaires atypiques

The search for biological and clinical significance of equivocal urinary cytology has emerged as the most promising application of fluorescence in situ hybridization (FISH). Using the multiprobe UroVysion assay, a negative FISH result in the presence of atypical urothelial cells favors the presence of reactive, benign alterations and helps to avoid unnecessary invasive procedures. However, a negative FISH result in case of a negative or equivocal cytology does not exclude low-grade urothelial neoplasia. Equivocal findings are a notorious problem after conservative treatment, particularly after BCG immunotherapy of carcinoma in situ, where even benign reactive changes can appear worrisome. In this situation, a positive FISH result in spite of non-high grade cytology independently indicates persistent or recurrent urothelial carcinoma. However, chromosomal abnormalities are not restricted to malignancy but may also occur in benign cells. Tetraploidy with a balanced duplication of the whole genome, or polyploidy can occur in non-neoplastic conditions of the bladder such as Decoy cells, radiotherapy-induced changes and urolithiasis. Thus, a positive FISH result in a patient with a history of pelvic irradiation does not prove cancer unless there is unequivocal 9p21 deletion. Recent studies show that an aggressive workup of patients with a suspicious cytology + positive UroVysion result and negative cystoscopy is not currently justified. However, multi-target UroVysion FISH remains an excellent tool to improve diagnosis in urinary cytopathology, provided that FISH results are interpreted in the light of the clinical situation, and that one reminds that FISH adds no diagnostic value in case of clearly positive, high-grade cytology.