<p>Materials and method for treating cancer and screening for anti-neoplastic agents are provided. These materials and methods can include sphingosine 1 -phosphate antagonists that bind to sphingosine- 1 phosphate receptor subtype 3. Antibodies and aptamers that selectively bind to an epitope in the extracellular loop between transmembrane domains two and three of sphingosine- 1 -phosphate receptor subtype 3 are provided.</p>
