SS300 - Watch and Wait for Mid-Rectal Cancers is Associated with Favorable Outcomes

Purpose/Background: The adoption of watch and wait for patients with rectal cancer has increased. Organ preservation allows oncologic outcomes equivalent to total mesorectal excision (TME) without post-operative morbidity. Digital rectal examination is an important part of watch and wait surveillance for low rectal cancers but not for those with mid rectal cancers beyond reach of the examining finger. The primary objective of this study is to determine if mid-rectal cancers have favorable watch and wait outcomes compared to patients with low rectal cancers. The primary hypothesis is that patients with mid-rectal cancers achieve clinical response rates that allow watch and wait entry, and that MRI and surgeon-led endoscopy surveillance allows accurate determination of clinical response to total neoadjuvant therapy (TNT) even when beyond the reach of the examining finger.

Methods/Interventions: An institutional prospectively maintained colon and rectal surgery database was queried for all rectal cancer patients between 2017 and 2025. These data were supplemented by data from the institutional tumor registry. Primary outcome was the watch and wait entry rate for patients with low- vs mid-rectal cancers. Other outcomes included regrowth rates, regional and distant recurrence, survival, and complication rates for those not in watch and wait who undergo upfront TME. Patients with metastatic disease precluding a potentially curable approach were excluded. Low rectum was defined as 0-6cm above the anal verge by staging MRI.

Results/Outcomes: There were 147 patients with rectal adenocarcinoma presented at multidisciplinary tumor board. Of these, 66 patients had clinical responses to TNT that allowed entry into watch and wait and 81 patients had incomplete responses that warranted up-front TME. Of those patients with low rectal cancers, 50.0% entered watch and wait surveillance compared to 40.7% of the mid rectal group (p=0.262). There were no significant differences in patient characteristics, MRI clinical staging, and neoadjuvant therapies between low and mid-rectal cancer groups. Regrowths occurred in 12.5% (n=5) of low and 15.4% (n=3) of mid rectal cancers (p=0.739). The low rectum group had 1 salvage APR and 4 salvage TAE while the mid-rectal group had 3 salvage TME and 1 salvage TAE. The low rectum group had 2 distant recurrences and the mid-rectal group had none. There was one death-with-disease in the low rectum group and one disease-free death in the mid-rectal group. There was no significant difference in complications (57.1% vs 54.5%, p=0.817) including anastomotic leaks (2.9% vs 4.5%, p=0.156) between low and mid-rectal groups with upfront TME.

Conclusion/Discussion: Though digital rectal examination provides important information for patients with low rectal cancers in watch and wait surveillance after a clinical complete response to neoadjuvant TNT, patients with mid rectal cancers beyond the reach of the examining finger also have favorable outcomes with MRI and surgeon-led endoscopic surveillance.

Table 1. Watch and Wait Patient Characteristics and Outcomes