DCIS (ductal carcinoma in situ) was first described in 1972, and is widely believed to be an indicator of the likelihood of developing invasive (i.e. metastasing) breast cancer.
Since the widespread introduction of x-ray based breast screening programmes (which can easily detect small-scale calcium deposits, indicative of 'abnormal' tissue) the incidence of DICS diagnosis has increased dramatically. DCIS is currently graded into three types - low, medium and high. The current treatment regime (esp. for high-grade) usually involves so-called 'lumpectomy' i.e. surgical removal of the abnormal tissue. However, the ongoing lumpectomy strategy, which has been running for several decades in many countries, has as yet had no effect on the incidence on invasive breast cancers in any country where the programme exists.
It is currently unknown which types of DCIS lesions may or may not turn into life-threatening disease - and as yet there are no published data quantifying the likelihood of that happening.
For a current (2016) overview, see: Finding the balance between over- and under-treatment of ductal carcinoma in situ (DCIS)