Teaching point:
The fact that this patient's tumor invades through to the subserosa makes it a Dukes-Aster-Coller stage B2 or C2. B2 has a 5-year survival rate of 60-65% and C2 has a 5-year survival rate of 25%. The difference in stage is dependent on the presence of positive lymph nodes (the most significant prognostic indicator), which cannot be determined by imaging alone.

Final staging is based on pathology and not on clinical presentation. Therefore, surgery is required to remove the lesion (check for negative free margins) and regional lymph nodes (check for micrometastases). In a patient with a T3 lesion such as this (TNM system: T3 signifies invasion through the muscularis propria into the subserosa, or into the nonperitonealized pericolic or perirectal tissues), local excision requires a small mass (<3 cm diameter), minimal wall invasion, tumor-free margins, and post-operative adjuvant therapy. This tumor is >5 cm above the anal verge and thus requires a low anterior resection with primary anastomosis, as opposed to an abdominoperineal resection with permanent colostomy.

Finally, based on the extent of invasion of this tumor into the bowel wall, chemotherapy as well as radiotherapy are required regardless of the presence or absence of positive lymph nodes.