How would you address squamous cell carcinoma in situ focally present at the bronchial margin after lobectomy?

Rare event so not great data to guide decision-making here. Technically, this is an R1 resection but a positive resection margin due to residual microscopic invasive disease is a distinct entity from a positive margin due to CIS. There is a nice review from JTO that covers this topic (Vallières et al., PMID 21918388) and clearly states that the presence of CIS at margins does not impact prognosis. Not all CIS is going to develop into invasive disease and due to the multifocal nature of CIS, I wouldn't be confident I would be comprehensively covering the necessary volumes thus adding tox without a clear benefit. Would favor close observation in these cases.