Itchy breasts have many causes, and the least likely is breast cancer.  In girls going through puberty, itchy breasts are often caused by the skin stretching as the breasts grow.  Often women develop itching from the same type of organisms that cause athlete's foot, especially under their breasts or in their armpit.  If plain lotion isn't helping, you might try an anti-fungal powder.  Show the itchy place to your mom or a trusted adult to see if a doctor needs to take a look, but most of the time itching doesn't need a doctor's attention.  Reading this Teen Guide to Normal Breast Development will give you some guidelines for what to worry about and what is typical.  Good for you for paying attention to your health and asking questions.  Those skills will help you all your life.