Non-invasive cancer that originates in lobules or ducts.
Typically asymptomatic and diagnosed at screening.
Tamoxifen can be used to prevent ductal carcinoma in situ (DCIS) disease progression and lobular carcinoma in situ (LCIS) progression to invasive carcinoma.
Screening is recommended by most organisations issuing guidelines, in all women aged ≥40 years with annual bilateral mammography.
Diagnosis is with mammography, supplemented with other imaging, such as ultrasound or magnetic resonance imaging, and biopsy.
Some patients may decide to have preventative bilateral mastectomy.
There are different approaches. Margin width remains something that is debated.
Breast cancer in situ is cancer that is confined to the duct or lobule in which it originated and does not extend beyond the basement membrane. The cancer does not have access to distant spread through lymphatics or the bloodstream. Ductal carcinoma in situ (DCIS) is a potential precursor of invasive carcinoma and suggests that cancer will become invasive at that site. 
Lobular carcinoma in situ (LCIS) develops in breast lobule(s) and is usually found incidentally. Whereas DCIS predicts an increased risk of invasive ductal carcinoma developing at the site of a biopsy demonstrating DCIS, LCIS implies increased risk of invasive ductal or lobular carcinoma developing in either breast.  LCIS does not behave physiologically like cancer: cancer may never form, but LCIS is nevertheless a marker for increased risk. Similarly, a finding of LCIS does not imply that cancer will form at the diagnostic site. Consequently, treatment for LCIS is less formalised than for DCIS.
Director of Breast Surgery
ERS is an author of a reference cited in this monograph.
Dr Edward R. Sauter would like to gratefully acknowledge Dr Rachel L. Ruhlen, a previous contributor to this monograph. RLR declares that she has no competing interests.
Radboud University Nijmegen Medical Centre
CB is an author of a number of references cited in this monograph.
Assistant in the Division of Medical Oncology
European Institute of Oncology
AB declares that she has no competing interests.
Associate Professor in Epidemiology and Medical Oncology
Johns Hopkins School of Medicine and Bloomberg School of Public Health
KV declares that she has no competing interests.
Consultant Surgeon and Honorary Senior Lecturer
Edinburgh Breast Unit
Western General Hospital
GTN is a principal investigator for the IBIS-II trial, and is an author of a guideline cited in this monograph.
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