I have a small white pimple on my nipple – not the areola, my nipple. I squeezed it and a moist white substance came out. Is this something to be concerned about?
We have oil glands on our nipple called Montgomery glands, and these keep the nipples lubricated and soft. It sounds to me like one of your oil glands got blocked, and perhaps a tiny infection built up underneath. Just as you can get pimples on similar oily spots – your forehead, or nose – you can get them on or around your nipple.
That was probably pus that you squeezed out, a result of the blockage. Keep your eye on the spot; if it doesn't come back, then you won't need to worry. If it continues to appear, then you'd best see a doctor for some better treatment – an antibiotic, perhaps.
This doesn't sound at all like a breast cancer symptom; though, as with any breast change, you want to track it until it disappears, or see a doctor if it doesn't. Finally, you may want to read this: Nipple Issues: When to Worry, When to Wait.