Systematic literature review (SLR) of prognostic factors (PFs) in locally advanced rectal cancer (LARC) and mismatch repair deficient (dMMR)/microsatellite instability-high (MSI-H) rectal cancer (RC).

303 Background: Innovative immunotherapies arebeing developed to improve clinical outcomes in patients (pts) withdMMR/MSI-H LARC who respond poorly to the current standard of care. A comprehensive overview of PFs in dMMR/MSI-H LARC may provide insight into the natural history of this disease to inform clinical study design and pt risk stratification. Methods: Systematic searches of bibliographic databases (EMBASE, MEDLINE, Cochrane; 2013–2023) and congress websites (2021–2023) were conducted to identify PFs for tumor response and survival outcomes in adult pts with LARC (SLR1) and dMMR/MSI-H RC (SLR2). Given the expected high volume of evidence, SLR1 was limited to large observational studies (≥1000 pts) and clinical trials (≥100 pts); SLR2 had no such limits. Results: 95 of 2307 publications met the inclusion criteria for SLR1. Of the PFs reported in ≥20 studies, older age, more lymph node involvement or fewer nodes assessed, higher T-stage or larger tumor size, higher histologic grade, and more comorbidities were most frequently significantly associated with poorer patient prognosis (Table). 3 of 289 publications met the inclusion criteria for SLR2. Neoadjuvant chemoradiation therapy (CRT) compared to chemotherapy (CT) was associated with statistically significant worse disease-free survival (DFS) and distant metastasis-free survival (DMFS), while T- or N-stage, age, and sex did not significantly impact these outcomes. Low vs middle tumor localization was also associated with worse DMFS. Stage III and IV disease were associated with worse RC-specific survival, while surgical procedure (segmental vs extended) showed no difference in overall survival (OS). The addition of neoadjuvant CRT or adjuvant CRT/CT to surgery alone had no impact on OS but was associated with worse DFS. Conclusions: Evidence regarding PFs in dMMR/MSI-H RC is scarce and may limit its interpretability, highlighting the need for further research that may be informed by the PFs identified from SLR1. The results from these SLRs may be helpful for optimizing patient management and treatment decision making, and to further contextualize RC clinical trials. PFs reported in ≥20 studies with ≥75% of studies reporting significant results in pts with LARC. PF Studies reporting PF (n) Studies reporting significant* impact of PF on prognosis (%) Poorer prognosis group Top 2 most frequently reported outcomes Age 59 81.4 Older OS, DFS Lymph node involvement/assessment 55 78.2 Yes or higher N stage OS, DFS T-stage or tumor size 53 79.2 Higher or larger OS, DFS Histologic grade 37 75.7 Higher OS, pathological complete response (pCR) Comorbidities 23 87.0 More OS, pCR *p-value <0.05 was considered significant as reported in the identified studies.