How would you treat an early-stage dMMR rectal squamous cell carcinoma in an otherwise healthy elderly patient?  

With no squamous cells in the actual rectum, I typically treat this as I would anal cancer—definitive chemoradiotherapy, ideally with capecitabine/5-FU-mitomycin (Day 1 only).

I have only seen one MSI-H anal SCC; it was metastatic, and I treated it with chemo-immunotherapy. Hard to know the contribution of components. Your rectal SCC is likely anorectal (low rectal tumor) and should be treated like an early-stage anal cancer. I would recommend CRT. While it's attractive t...