ESTRO 2024 - Abstract Book

S1526

Clinical - Lower GI

ESTRO 2024

There was no difference in the incidence of grade 3 CTCAE bowel toxicity between cohorts. Equal incidences of other adverse events (not limited to bowel toxicity) were found in each cohort (18.75%, N=3) as seen in Table 1.

The average TRG for the DPD deficient cohort was 2.9 and 2.6 for the non-DPD deficient cohort suggesting a 0.3 difference. The 1-tailed Mann-Whitney U test failed to identify any statistically significant difference (P=0.1335) between cohorts.

There was no statistical significance between any metrics as shown in Table 1.

DPD deficient (%) (N=16)

Non DPD deficient (%) (N=16) 14 (87.50%) 1 (6.25%) 1 (6.25%) 3 (18.75%) 13 (81.25%) 4 (12.5) 12 (87.5%) 0 (0%)

CTCAE toxicity

grade

bowel

0 (no bowel toxicity)

13 (81.25%)

1

2 (12.5%)

2

1 (6.25%)

3

0 (0%)

Other adverse events

Yes

3 (18.75%)

No

13 (81.25%)

Capecitabine stopped

Yes

3 (18.75%)

No

13 (81.25%)

TRG

1 2 3

2 (12.5%) 2 (12.5%) 9 (56.25%)

0 (0%)

8 (50%)

7 (43.75%) 1 (6.25%)

4

3 (18.75%)

Average

2.9

2.6

Conclusion:

The recent change in current practice for DPD deficient rectal cancer patients who now receive a Capecitabine DR appears safe.

There was no incidence of CTCAE grade 3 bowel toxicity, with CTCAE grade 2 as the highest grading. Importantly, N=13 (81.25%) and N=14(87.5%) in the DPD deficient and non-deficient cohorts respectively did not experience any bowel toxicity. Equal incidences of other adverse events were found between cohorts. TRG showed no statistical significance between cohorts (DPD deficient: non-DPD deficient) suggesting TRG appears unaffected by a reduced Capecitabine dose. Future studies with larger cohort sizes and long term follow up to obtain recurrence rates would be beneficial to improve reliability of such statements.

Poor adherence to published dose escalation recommendations was revealed. After week two, Capecitabine was dose increased to 75%, not 12.5% increases per week as recommended, yet the impact appears insignificant. The