What is a hypoechoic nodule of the breast measuring 0.5 is well circumscribed and ovoid?

Benign. . These are hallmarks of something that is not cancerous. It also needs to show no shadowing, and may have enhanced through-transmission. Probably a benign fibroadenoma, needs no follow up unless stated so by the interpreting doctor. Could be a cyst, same answer: should be benign. If it shadows, is tall, not completely smooth, or big all bets are off. Biopsy is easy with a core needle if needed.