Abstract 430P
Background
Complete pathological response (pCR) is achieved in 10-20% of rectal cancers when treated with preoperative short-course radiotherapy (scRT) or long-course chemoradiotherapy (CRT) and in 28% with total neoadjuvant therapy (TNT) including scRT/CRT with chemotherapy. pCR is linked to better outcome. Which clinical or imaging factors predict pCR?.
Methods
All patients with preoperative treatment and delay to surgery in Uppsala-Dalarna (n=359, 2010-2018) and Stockholm (n=635, 2006-2016) were included. Data cut-off was June 1, 2019. Comparison of pCR versus non-pCR was performed with binary logistic regression models.
Results
pCR was achieved in 12% of the 994 patients: (8% [33/435] with scRT, 13% [48/358] with CRT and 21% [43/201] with TNT). In univariate analyses, age <70 (OR 2.09; CI95% 1.4-3.2), cT1-2 (2.47; 1.3-4.9), (but not cT3 1.25; 0.8-1.8) with cT4 as reference, tumour length <4cm (1.83; 1.1-2.9), CRT (1.89; 1.2-3.0), and TNT (3.31; 2.0-5.4) with scRT as reference, normal leukocytes (2.37; 1.2-4.8), thrombocytes (4.58; 1.1-19.2), and CEA (2.04; 1.3-3.3) predicted superior pCR rates, but not cN0, cMRF-, cEMVI-, level above anal verge ≥7cm, interval to surgery, or normal haemoglobin. In multivariable models (n=735), CRT (OR 2.80; 1.4-5.5), TNT (5.25; 2.6-10.4) with scRT as reference; cT1-2 (3.39; 1.1-8.7), (but not T3 1.36; 0.8-2.2) with cT4 as reference, tumour length <4cm (2.20; 142-4.0), and normal CEA (1.67; 1.0-2.8) remained significant, but not age and leucocytosis (thrombocytes not included due to 450 missing values).
Conclusions
Treatment modality (OR 4.66 for TNT and OR 2.57 for CRT) was the strongest factor for achieving pCR and cT1-2, tumour length, and normal CEA remained significant in the multivariable model. These factors are important as patients achieving pCR are candidates for organ preservation strategies.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Swedish Cancer Society, Stockholm Cancer Society.
Disclosure
All authors have declared no conflicts of interest.