Novel Evidence That Neuroblastoma and Rhabdomyosarcoma, Two Types of Small Round Blue Cell Tumors, Frequently Infiltrate Bone Marrow and Express Functional Erythropoietin Receptor (EpoR)—therapeutic Implications
Authors: Poniewierska-Baran Agata , Schneider Gabriela , Ratajczak Janina , Kucia Magdalena , Ratajczak Mariusz Z 
Published: October 2019

Abstract
Background : The erythropoietin receptor (EpoR) is expressed by cells from the erythroid lineage; however, evidence has accumulated that it is also expressed by some solid tumors, and recently our group demonstrated the presence of functional EpoR on human and murine germline-derived cell lines, including teratocarcinomas and ovarian cancer cells (J Ovarian Res. 2014 Jun 17;7:66). Neuroblastoma (NRB) and rhabdomyosarcoma (RMS), the most common soft-tissue sarcomas of adolescents and children and described as “small round blue cell tumors”, frequently infiltrate the BM to such a degree that they mimic acute lymphoblastic leukemia. These tumors express several cancer testis antigens (CTAs), which are characteristic of germline-derived cells. This is intriguing because of the 150-year-old “embryonic rest hypothesis of cancer development” by Rudolf Virchow and Julius Conheim, in which malignancies may develop from dormant embryonic/germ cells residing in adult tissues. Small round blue cell tumors, including in NRB and RMS, are potential candidates for such malignancies.
Hypothesis . Based on our observations that germline-derived tumors express functional EpoR and that NRB and RMS express CTAs, we asked whether these pediatric sarcomas express functional EpOR as well.
Materials and Methods . In our studies we employed four human NRB, eight RMS cell lines (4 embryonal-type RMS cell lines and 4 alveolar-type RMS cell lines), and mRNA samples obtained from patients. Expression of EpoR was evaluated by RT-PCR and FACS. The functionality of EpoR in NRB and RMS cell lines was evaluated by chemotaxis, adhesion, and direct cell proliferation assays. In some of the experiments, RMS and NRB cells were exposed to vincristine (VCR) in the presence or absence of EpO to test whether EpO may impair the therapeutic effect of VCR.
Results . We found expression of EpoR mRNA in all tested cell lines and patient samples. Importantly, EpoR has been found to be functional in all NRB and RMS cell lines tested, responding to stimulation by erythropoietin (EPO) by an increase in chemotaxis, adhesion, and phosphorylation of MAPKp42/44 and AKT. Moreover, we found that EPO stimulates proliferation of NRB and RMS cells and increases their resistance to VCR.
Conclusions . Our data for the first time indicates that human pediatric sarcomas express functional EpoR. This finding has important clinical implications, as EPO is frequently employed to ameliorate chemotherapy-related anemia. The presence of functional EpoR on pediatric sarcoma cells indicates that EPO supplementation may have the unwanted side effect of tumor progression. Finally, the presence of functional EpoR on both NRB and RMS cells and germline-derived tumors as well as expression of CTA antigens by these cells supports the hypothesis that pediatric sarcomas may develop in developing tissues from embryonic remnants with germline potential.

Disclosures
No relevant conflicts of interest to declare.