Usefulness of Restaging Pelvis Magnetic Resonance Imaging After Neoadjuvant Concurrent Chemoradiotherapy in Patients With Locally Advanced Rectal Cancer

The impact of neoadjuvant concurrent chemoradiation on exosomal markers (CD63 and CD9) expression and their prognostic significance in patients with rectal adenocarcinoma

Introduction: Exosomes have pivotal roles in cancer development. The impact of neoadjuvant concurrent chemoradiation (NCCR) on exosomal markers (CD63 and CD9) expression and their prognostic significance in patients with rectal adenocarcinoma are yet to be explored.

Materials and Methods: Between 2015 and 2018, 33 patients had rectal adenocarcinoma treated with NCCR and had pre-NCCR biopsy and post-NCCR resected rectum. CD63 and CD9 expression was assessed by immunohistochemistry (IHC). The short-term surrogate endpoint neoadjuvant rectal (NAR) score was used for assessment of prognostic significance. Un-Paired t-test was used for statistical analysis.

Results: The mean tumor CD63 and CD9 scores in pre-NCCR biopsy vs. post-NCCR resected rectum were 106 vs. 165 (P = 0.0022) and 136 vs. 215 (P < 0.0001) respectively. The mean tumor CD63 and CD9 scores respectively in pre-NCCR biopsy was 99 and 130 in patients with low-intermediate NAR score compared to 117 and 144 in patients with high NAR score (P = 0.4934) (P = 0.5519). The mean tumor CD63 and CD9 scores respectively in post-NCCR resected rectum was 155 and 205 in patients with low-intermediate NAR score compared to 180 and 230 in patients with high NAR score (P = 0.3793) (P = 0.2837).

Conclusions: The expression of the exosomal markers (CD63 and CD9) increased in patients with rectal adenocarcinoma after treatment with NCCR. The exosomal markers (CD63 and CD9) may have a prognostic significance. There was a trend for higher CD63 and CD9 expression in patients with high NAR score compared with low-intermediate NAR scores. The lack of statistical significance is likely due to the small sample size.

The concept and use of the neoadjuvant rectal score as a composite endpoint in rectal cancer

There is no universally accepted instrument to use as a validated surrogate endpoint for overall survival in phase 2 and phase 3 multimodal rectal cancer trials using chemoradiotherapy. Efforts are hampered by the inaccuracy of clinical TNM staging, the variability of indications for neoadjuvant treatment, and diverse definitions of tumour regression grade. Pathological complete response is commonly used, but fails to capture information from the majority of patients. The neoadjuvant rectal score categorises response and downstaging from the entire trial population to identify whether or not a novel treatment group in a chemoradiation trial is superior by predicting overall survival outcomes. Additionally, the neoadjuvant rectal score assesses the difference between initial clinical and pathological T stage and the presence or absence of nodal involvement after treatment. The neoadjuvant rectal score has been conceptually, but incompletely, statistically validated by two independent trial datasets. However, a fundamental weakness of the score is that no preoperative phase 3 trials in locally advanced rectal cancer in the past 20 years have provided a significant benefit in overall survival to statistically validate the neoadjuvant rectal score as a surrogate endpoint for overall survival. We review the robustness, practical value, applicability, generalisability, advantages, and disadvantages of the neoadjuvant rectal score as a surrogate endpoint for overall survival and recommend how this score could be improved and be acceptable as a standard endpoint in studies investigating neoadjuvant chemotherapy and chemoradiation in patients with rectal cancer.