A single institution retrospective study evaluating mitomycin dosing during chemoradiation in anal squamous cell carcinoma.

7 Background: Mitomycin (MMC) is used concurrently during chemoradiation (CRT) treatment for non-metastatic anal squamous cell carcinoma (SCCA). The most effective dosing of MMC is not established, and due to concerns for tolerability, many have adopted a dose-reduction strategy. This study evaluates differences in treatment response and recurrence between MMC dosing in this setting. Methods: Demographics, age, smoking history, staging, and treatment history were collected for patients with non-metastatic SCCA treated with CRT from January 2011-September 2024 at a tertiary cancer center. Chi-square analyses compared categorical variables, and ANOVA tests were used to compare treatment response and recurrence between 3 MMC doses (12mg/m 2 x 1 dose with cap of 20mg, 10mg/m 2 x 2 doses, 10mg/m 2 x 1 dose). Results: There were 124 patients, 6 of whom were excluded due to lack of follow up. Of the 118 included, 70% were female, 16% Black, 3% Hispanic/Latino, and 58% current/former smokers. Median age was 61 years (31-98). Thirty-three (28%) pts were treated with MMC 12mg/m 2 , 71 (60%) with 10mg/m 2 x2 doses, and 14 (12%) with 10mg/m 2 x1 dose. Stage I included 18% of 12mg/m2, 7% of 10mg/m 2 x2 doses, and 7% of 10mg/m 2 x1 dose; stage II included 18% of 12mg/m2, 37% of 10mg/m 2 x2 doses, and 50% of 10mg/m 2 x1 dose; stage III included 64% of 12mg/m2, 56% of 10mg/m 2 x2 doses, and 43% of 10mg/m 2 x1 dose. A total of 39.7% were treated with MMC/capecitabine and 60.3% with MMC/fluorouracil. Complete response was achieved in 91% receiving the 12mg/m 2 , 75% receiving 10mg/m 2 x2 dose, and 71% receiving 10mg/m 2 x1 dose (p=0.13, Table 1). Using logistic regression with MMC dose, stage, age, and smoking status as independent predictors, the odds of achieving complete response were lower in 10mg/m 2 x2 doses (p=0.03) and 10mg/m 2 x1 dose (p=0.03) compared to 12mg/m 2 . Local, regional, or metastatic recurrence occurred in 15% of pts receiving 12mg/m 2 , 17% of 10mg/m 2 x2 doses, and 7% of 10mg/m 2 x1 dose. No significant difference was seen in local (p=0.52), regional (p=0.93), metastatic (p=0.87), or overall recurrence (p=0.65) between the MMC doses. Conclusions: Odds of achieving complete response was greater with 12mg/m 2 dosing. Local, regional, and metastatic recurrence were similar among the different MMC dosing cohorts. Differences in tolerance and side effects should be delineated to guide individualized dosing of MMC.