extensive dcis w/comedo necrosis

Hi there, and welcome to the club no one wants to join.     Ariom has given you good advice.   In terms of whether or not you'll need a mastectomy, that depends on both what the docs mean by extensive (since it's not a technical term) and how large your breasts are - the reason you would need a mastectomy over a lumpectomy has nothing to do with the aggressiveness of the cancer, as both treatments are equally successful, but it has to do with the cosmetic result that could be achieved.  Or as I put it when helping my mom to make the same decision "What would you be left with".   Again, the answer will depend on the size of your lesion relative to your breast, as well as the location.   In her case, she would be losing the nipple either way, plus wouldn't be left with much as she is relatively small-busted, so chose a mastectomy.   I am larger, had a smaller area of cancer and mine was nowhere near the nipple so I was a better lumpectomy candidate.

As for the comedo necrosis, that does indicate a more aggressive form of DCIS, but as long as it is still DCIS doesn't really change your treatment plan, so you will have to wait for the final pathology from whatever surgery you have to know whether there were any hidden areas of invasive cancer.  Having extensive DCIS with comedo necrosis makes that more likely than if you had a small area of less aggressive DCIS, but is by no means a certainty, and hopefully they will find nothing but DCIS.    Even if they do find a small area of invasion, as long as it remains really tiny, it doesn't really change your prognosis or treatment much.