ER+ HER2- DCIS is the most common breast cancer from what I was told and read.

I think 'DCIS invasive' is used as it describes this cancer, starting in the milk ducts, by location and category, but adds that some cancer cells were found outside of the duty. But contiguous to the main tumor. I'm guessing that most early-stage DCIS tend to become "invasive" over time.

A friend had a small non-invasive DCIS, Stage 0 that oncolgist(s) advised surgery and radiation for as the cancer was on the chest wall resting 'too close' to bone. So there are a lot of factors that play into diagnosis treatment. (Her OncotypeDX risk of recurrence was only 2% though. So she didn't do chemo or AI meds. She has rheumatoid arthritis and the AIs were hard on her.)

The point is that there are so many factors that come into play. I hope everyone gets a second opinion on this stuff as legitimate opinions can vary and be worth considering.