CYCLIN D1 AND WILMS TUMOR TRANSCRIPTION FACTOR-1 (WT1): POTENTIAL DIAGNOSTIC AND THERAPEUTIC MARKERS IN SMALL ROUND BLUE CELL TUMORS OF CHILDHOOD

Wilms tumor 1 (WT1) gene, firstly cloned in 1990 in the childhood kidney cancer Wilms tumor, is a gene located on chromosome 11p13, which encodes zinc-fingers protein characterized by multiple alternative isoforms, with important regulatory functions in cell growth and development. The protein Cyclin D1 (CD1), encoded by the CCND1 gene, belongs to the highly conserved cyclin family, whose members function as regulators of CDKs (cyclin-dependent kinase) through-out the cell cycle. CD1 serves as a key sensor and integrator of extracellular signals of cells to promote progression through the G1 S phase of the cell cycle, playing several biological roles in promoting cellular proliferation/differentiation, apoptosis/survival, migration, metabolism, and neuronal regeneration. We focused on the immunohistochemical expression profile of WT1 protein and CD1 in: i) human fetal tissues in order to provide suggestions about their role in the development of tissues and organs; ii) a large series of pediatric small round blue cell tumors, including peripheral neuroblastic tumors (neuroblastomas, ganglioneuroblastoma, ganglioneuromas), Ewing s sarcoma/pPNET (EWS/pPNET), embryonal and alveolar rhabdomyosarcomas, lymphoblastic lymphoma and Wilms tumor, to assess the potential utility of these markers in the differential diagnosis of these tumors; iii) Ewing Sarcoma derived by culture of human Ewing Sarcoma cell lines, inoculated in a group of mice, in order to establish if the immunohistochemical expression of WT1 and Cyclin D1 is comparable to that observed in human neoplastic tissues. All cases of rhabdomyosarcoma regardless of subtype exhibited strong and diffuse cytoplasmic staining (>50% of neoplastic cells) for WT-1. In contrast, this marker was absent from lymphoblastic lymphoma (either B- or T-cell precursors), EWS/pPNET, neuroblastoma. All cases of EWS/pPNET and the undifferentiated/poorly differentiated neuroblastomatous component of all peripheral neuroblastic tumors exhibited strong and diffuse nuclear staining (>50% of neoplastic cells) for cyclin D1. In contrast, this marker was absent from rhabdomyosarcoma (regardless of subtype) and lymphoblastic lymphoma (either B- or T-cell precursors), whereas it was only focally detected (<5% of neoplastic cells) in some cases of Wilms tumor (blastemal component) and desmoplastic small round cell tumor. WT1 protein is a useful marker for diagnosis of malignant tumors in children and adolescents. However, it should be emphasized that not only Wilms tumor, but also other neoplasms, including desmoplastic small round cell tumor, malignant rhabdoid tumor, can express WT1 protein at nuclear level. WT1 is helpful as an additional immunomarker to conferming the diagnosis of both embryonal and alveolar rhabdomyosarcoma, being strongly and diffusely expressed in these tumors. The present study first shows that CD1 is an additional, highly sensitive immunomarker of EWS/pPNET, along with CD99 and FLI-1. The common CD1 overexpression in pediatric/adolescent soft tissue EWS/pPNETs and its absence in rhabdomyosarcoma (embryonal/alveolar subtypes) make this marker suitable for their differential diagnosis [160]. The expression of cyclin D1 in the Human Ewing sarcoma mouse xenograft could be the basis for new experiments on animals in order to planning new target therapies.