LCIS in Lumpectomy Path Report after MIC diagnosis on biopsy

There is no way of knowing, at least for sure, whether the microinvasive cancer came from LCIS or if LCIS on path is something clearly different. When they look at genetic analysis of tissues, for women that previously had 'just' LCIS then later or simultaneously detected invasive breast cancer, sometimes the LCIS was genetically related to the invasive cancer, and sometimes it was not. Normally, with LCIS only, the LCIS is found in multiple spots in a breast, and often in both breasts. (They know this because previous to about mid-1990, they routinely did bilateral mastectomies on women with LCIS and they could look at the mastectomy specimens.) We don't know how LCIS puts one at higher risk of breast cancer (in other words, the mechanism that LCIS increases breast cancer risk.) When women with 'just' LCIS go on to get invasive breast cancer, sometimes/often the invasive cancer is not at, but adjacent to, the previously known LCIS. The area that later became cancerous looks normal under screening.

I doubt if your LCIS diagnosis will cause additional surgery, unless there are suspicious areas that were not removed. At least half of the women with classic known LCIS only will never go on to get DCIS or invasive breast cancer. They can't remove 'all the LCIS spots' because they don't know where they are, unless perhaps they do bilateral mastectomies. But even bilateral mastectomies will not remove all breast tissue, any of which could contain LCIS.

When someone is diagnosed with LCIS on biopsy, they normally do an excision to see if there is something worse in the vicinity. They normally don't try to remove all of the LCIS because they don't have an idea where it is. Most LCIS is detected as an incidental finding when they do biopsies or lumpectomies.