Final answer:
DCIS is noninvasive because it remains within the boundaries of the breast ducts and has not spread to surrounding tissue. It's a pre-malignant condition that has the potential to develop into invasive cancer if untreated.
Step-by-step explanation:
DCIS, or Ductal Carcinoma In Situ, is considered noninvasive because it has not spread beyond the milk ducts into any normal surrounding breast tissue. DCIS is a type of pre-malignancy which means it's a condition that has the potential to progress to cancer, specifically invasive cancer, if it is not treated. Being a carcinoma in situ, it lies at the high end of the spectrum in terms of potential to become an invasive tumor but is not yet invasive itself. In other words, it remains contained within the boundaries of the ductal system of the breast.