When a biopsy shows SCCIS broadly transected at the deep margin, do you routinely refer for Mohs to rule out occult invasive SCC, or do you proceed with destructive modalities (e.g., ED&C) outside the H-zone?

Most series find occult invasion in about 3–16% of biopsy-proven SCCIS.

In the only dedicated series of SCCIS transected at the base, the rate was about 10%, and more than half of those cases had no residual tumor at all.

When invasion does turn up, it's usually superficial and well differentiated.