Peripheral neuroectodermal tumors (PNET) have an unsatisfactory outcome when treated with standard approaches. Among novel treatments, the use of biological response modifiers has rarely been reported in this group of malignancies. We have previously demonstrated that both all-trans retinoic acid (ATRA) and interferon á (IFNá) can inhibit proliferation of human PNET cells and that ATRA can up-regulate IFNá receptor expression in vitro. In this study we evaluated the anti-tumor effects of ATRA and IFNá in PNET cells in vitro and in a human PNET xenograft model, using CHP100 cells. A synergistic inhibitory effect of ATRA and IFNá was observed on CHP100 cells in vitro. On the contrary, a significant inhibition of tumor growth was observed in mice treated with ATRA alone, whereas neither IFNá nor the combination of ATRA and IFNá, reached a statistically significant anti-tumor effect. Histologic examination of tumors revealed the presence of necrosis upon treatment with IFNá, whereas almost no necrosis, but a more differentiated morphology, confirmed by electron microscopy analysis, was associated with the ATRA containing treatments. Taken together these data show an in vitro and in vivo anti-tumor activity of ATRA in human PNET cells, although no synergism of ATRA and IFNá was observed in our xenograft model.

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