Does the presence of LCIS on pathology in a patient with IDC impact your decision to offer APBI?

It doesn’t change the decisions for APBI with all other factors being favorable.

We offer APBI to invasive lobular also if it meets all criteria and had MRI breast done as part of the evaluation.

I admit that it does, although this is a data-free zone! Associated LCIS is allowed by consensus statement criteria, but if the bed-to-breast size ratio is suboptimal, I often just do ultrahypofractionated whole breast instead.

Most probably, it wouldn't change the outcomes if it's a classic LCIS.

If it's a pleomorphic LCIS, it should be considered as a DCIS, and many argue that it's akin to a high-grade DCIS, with a high likelihood of hormone-receptor negative status, and sometimes with necrosis. Margins >2 mm are desired...