What is 'refractile' cell morphology?
From the Biology Online Dictionary, refractile refers to:


  ... the ability of cellular granules to refract or scatter light.


Tumor cells can be more "dense", as they are usually rapidly dividing, and so need extra ribosomes to maintain protein production, may have a higher DNA/RNA content reflecting increased transcription and duplication, more mitochondria to power the cells, etc. This can alter the refractive index of a suspension of tumor cells as compared to organ-matched normal cells, for example.