How fast does a benign breast tumor grow?

Variable: Different tumors grow at different rates. In general it takes a breast cancer about four years to become palpable from the time of onset. If left untreated a breast cance has an average life span of about four years from the time of diagnosis. These are average figures with wide variations among different tumors and patients.

Usually slow: The general guideline for a benign lesion (i.e. Fibroadenoma) is ~ 10%/year. Over a long period of time (15-20 years) they can actually atrophy and regress.