When would you offer post-operative therapy to a resected non-melanomatous skin cancer with a solitary positive node?

I treat them all. If they are fit enough for surgery, their prognosis is good enough to treat.

If the lymph node is smaller than 3 cm, then there might be a case to forgo adjuvant lymph node basin radiotherapy based on this study:

Ebrahimi et al., PMID 21472887

However, one would want to confirm that an adequate lymphadenectomy and pathologic review of the specimen was performed. Also, consider...

The ASTRO skin carcinoma guideline (Likhacheva et al., PMID 31831330) recommends postoperative radiotherapy for clinically node-positive patients with the exception of single <3 cm cervical node without ECE (Table 4, #1; strong recommendation; moderate quality of evidence).

I would treat for a 4 cm n...