Ductal carcinoma in situ (DCIS) is the name for abnormal changes in the cells in the milk ducts of the breast. ‘In situ’ means ‘in place’. The abnormal cells stay inside the milk ducts, and do not spread into the surrounding breast tissue.  

DCIS can be found in women at any age, but most are aged 50 to 59 years when their DCIS is found. In Australia, about 1,600^[2] women are diagnosed with DCIS each year. DCIS can also develop in men, but this is very rare. 

DCIS is not life-threatening, but it does have the potential to turn into invasive breast cancer if not treated. Women who are diagnosed with DCIS are about 4 times as likely to develop invasive breast cancer as women of a similar age who have not had DCIS.^[3] 

DCIS cannot usually be felt but is found by mammogram or ultrasound.^[4]