Associations between Response to Commonly Used Neo-Adjuvant Schedules in Rectal Cancer and Routinely Collected Clinical and Imaging Parameters

SIMPLE SUMMARY: We studied real-world patients with locally advanced rectal cancer receiving preoperative radiotherapy with or without chemotherapy. The aim was to find factors associated with complete response to therapy, i.e., no remaining tumour, that could be used to identify patients who would not need surgery in the future. Tumour stage and length, intensity of preoperative treatment, and laboratory factors, such as carcinoembryonic antigen (CEA), leucocyte counts, and platelets, were all associated with complete response. Treatment intensity mattered and when radiotherapy was combined with chemotherapy, 21% had a complete response compared to 8% with radiotherapy alone. A model for identifying patients with a better chance of achieving a complete response was developed using tumour stage and length, CEA, and leukocyte levels as factors predicting complete response. ABSTRACT: Complete pathological response (pCR) is achieved in 10–20% of rectal cancers when treated with short-course radiotherapy (scRT) or long-course chemoradiotherapy (CRT) and in 28% with total neoadjuvant therapy (scRT/CRT + CTX). pCR is associated with better outcomes and a “watch-and-wait” strategy (W&W). The aim of this study was to identify baseline clinical or imaging factors predicting pCR. All patients with preoperative treatment and delays to surgery in Uppsala-Dalarna (n = 359) and Stockholm (n = 635) were included. Comparison of pCR versus non-pCR was performed with binary logistic regression models. Receiver operating characteristics (ROC) models for predicting pCR were built using factors with p < 0.10 in multivariate analyses. A pCR was achieved in 12% of the 994 patients (scRT 8% [33/435], CRT 13% [48/358], scRT/CRT + CTX 21% [43/201]). In univariate and multivariate analyses, choice of CRT (OR 2.62; 95%CI 1.34–5.14, scRT reference) or scRT/CRT + CTX (4.70; 2.23–9.93), cT1–2 (3.37; 1.30–8.78; cT4 reference), tumour length ≤ 3.5 cm (2.27; 1.24–4.18), and CEA ≤ 5 µg/L (1.73; 1.04–2.90) demonstrated significant associations with achievement of pCR. Age < 70 years, time from radiotherapy to surgery > 11 weeks, leucocytes ≤ 10(9)/L, and thrombocytes ≤ 400(9)/L were significant only in univariate analyses. The associations were not fundamentally different between treatments. A model including T-stage, tumour length, CEA, and leucocytes (with scores of 0, 0.5, or 1 for each factor, maximum 4 points) showed an area under the curve (AUC) of 0.66 (95%CI 0.60–0.71) for all patients, and 0.65–0.73 for the three treatments separately. The choice of neoadjuvant treatment in combination with low CEA, short tumour length, low cT-stage, and normal leucocytes provide support in predicting pCR and, thus, could offer guidance for selecting patients for organ preservation.