Cancers that do not spread (in situ) are divided into two groups: ‘ductal carcinoma in situ’ and ‘lobular carcinoma in situ’. Especially after the 1980s, with the prominence of screening mammograms, the ability to diagnose more cases has led to an increase in the incidence of non-invasive (in situ) cancers from 1.4 percent to 10 percent in all breast biopsies and from 5 percent to 15 percent in all breast cancers.

Classic lobular carcinoma in situ: It is an important finding that increases the risk of breast cancer 8-10 times in both breasts. In addition to monitoring, such patients may be given some preventive medications such as tamoxifen. However, surgical interventions to remove both breast tissues (simple mastectomy) may also be preferred for preventive purposes. Cosmetically pleasing results can be obtained by performing prosthesis and similar surgical reconstructive procedures with plastic surgery interventions.

In situ ductal cancers (ISCC, intraductal cancer): Most of the time it does not show itself on examination.

It is characterized by irregular small calcifications and/or (pleomorphic microcalcification) bloody, transparent single duct nipple discharge. ISCC is considered to be the transition from normal cells to cancer cells with the potential to spread (invasive). Since it does not form a mass, it can be removed with wire or by marking with radioactive substances. If the cancer is unifocal, enough clean tissue is left around it. When radiotherapy (RT) is applied to the remaining breast tissue, the disease has a good clinical prognosis. If it is widespread in the breast, it is necessary to remove all the breast tissue (simple mastectomy) and in this case up to 100 percent complete recovery is seen. Involvement of axillary lymph nodes is rarely encountered in ISCC. For this reason, it may be necessary to remove the guard lymph nodes (sentinel lymph node biopsy) in some types of patients with worse features (high grade, etc.) due to the presence of cancer cells in the axillary lymph nodes.