what exactly are clear margins???

Clean margins are simply cancer-free ones. "Good" margins is a subjective term - more clear margin is better than less, so if they're saying you had "good" margins, that indicates a nice amount of non-cancerous tissue around the tumor. I had "okay" margins - clear but not big, primarily because my tumor was up between the chest muscle and skin, so there wasn't a lot of margin to be had.

I would think that having the bilateral would ease your mind on this, since they got all of the breast tissue that they could physically remove. Your margins were clean, your sentinel nodes were negative, and that's all good. ILC can often be "large" without having spread anywhere, and spread is the thing to avoid.

Your pathology report probably has specific information about the margins - mine had measurements for the margins on each side of the tissue studied.

For lumpectomy, clean margins are considered 1 to 2 mm of cancer free tissue surrounding the tumor. I'd imagine the measurements are the same for mast.

I get the impression that there is some variation in what margins are acceptable. Some doctors are satisfied with any margin free of malignancy, or with 1mm. Others want at least 2mm. My surgical report notes that some margins were less than 2mm, another less than 3, which suggests that some doctors want at least a 3mm margin. The main problem in my case, however, was that some margins were not clear.

The final report on the reexcision simply indicates that all samples submitted were "benign breast tissue," with no indication of the width of the margins.  The width of the samples, however, ranged from 2.7 to 4 cm, which suggests that the new margins were sizable. This is consistent with the surgeon's claim that she had removed a "generous" amount of additional tissue, no doubt hoping to avoid a third operation.

Lobular is tricky to excise. Even though my surgeon is quite experienced, she had to wait for the path report to be sure she had clear margins.