Background is white when cutting out a picture with the pen tool instead of transparent

The Background layer is a special type of layer which does not support transparency. You can convert it to a regular layer via Layer > New... > Layer from Background, or by double-clicking on it in the Layers panel (but not on the thumbnail).

Is there a white layer below the images layer you cut out?  Post a screen capture with your document open in photoshop where the layer palette is visible and has your layer visible in it.