eP445 - Rectal Cancer by Any Other Name

Purpose/Background: Squamous cell carcinoma of the rectum (rSCC) is a rare malignancy with only a few hundred cases reported in the literature and no known risk factors. Given its rarity, the pathogenesis and management of rSCC are also not well-defined. Although most rSCC are presumptively treated as squamous cell carcinoma of the anus (aSCC) with initial definitive chemoradiotherapy, it remains unknown if this management strategy is robustly generalizable. Differences in local microenvironment can profoundly affect tumor biology and the anatomic presentation of rectal squamous cell carcinomas is seemingly heterogenous. We aim to study our institution's experience with rSCC and its management, in hopes of better characterizing the pathology and outcomes of a disease we have found with alarmingly increased frequency in recent years.Methods/Interventions: We performed a retrospective review of a prospectively maintained single center database from 2012-2023 of 80 patients with invasive anorectal squamous cell carcinoma. Patients who had isolated rectal cancer (n=8) were compared with patients who had both anorectal (n=10) and isolated anal cancer (n=62). Interestingly, because most of our cohort were initially diagnosed starting 2020, we were unable to calculate an overall survival. As such, our primary outcomes were recurrence rate and initial response to therapy.Results/Outcomes: The mean age of our entire cohort was 59 years, with 62% females. In the isolated rectal group, 100% of the patients were female, 0% had HIV and 38% had HPV, when compared to 62% females, 22% with HIV, and 33% with HPV in the aSCC group respectively (p < 0.01, p < 0.01, p=0.24, respectively). Patients who presented with any rectal involvement had higher rates of T3/4 and node positive disease (88% and 88% for Isolated rectal and 50% and 88% for both anorectal) when compared to aSCC (36% and 31% respectively) (p=0.02 and p < 0.01 respectively). 25% of the isolated rectal patients initially presented with stage IV disease. Patients with any rectal involvement were more likely to undergo systemic therapy (100% vs 61%, p < 0.01) but equally likely to undergo radiation therapy (83% vs 82%, p=0.92). Complete response was present in 63%, 70%, and 56% of isolated rectal, both anorectal, and isolated anal groups respectively (p=0.66) with recurrence of 25%, 30%, 20% respectively with those who had an initially complete response (p=0.98).Conclusion/

Discussion: To date, studies comparing isolated rSCC with squamous cell cancer at other anorectal sites are limited. Patients with isolated rSCC are more likely to be female, have lower rates of HIV, present at a more advanced stage, and are more likely to undergo systemic therapy."Recurrence-free Kaplan-Meier Survival analysis

p=0.16
Overall survival Kaplan-Meier Survival analysis

p=0.16"