If the tumor is above the peritoneal reflection, and the patient has no metastatic disease, and the surgeon thinks a surgery with a negative margin is feasible, upfront surgery would be my choice followed by adjuvant chemo if appropriate.

Agree with both @Mital S. Patel and @Sakti Chakrabarti. Although, as mentioned, since it is locally advanced, I would favor a neoadjuvant approach. Depending on age, I've often resorted to doublet or triplet chemotherapy without any biologic. Still check MMR/MSI status. Increasing data to consider I...

AT 20cm, (adequately measured with a rigid scope) or proven non-rectal on an MR pelvis, we would treat these as colonic cancers -- if they are locally advanced and hence precluding an adequate surgery, would consider neoadjuvant chemotherapy to downstage prior to surgery.  There is some evidenc...