Selecting a TNT Schedule in Locally Advanced Rectal Cancer: Can We Predict Who Actually Benefits?

SIMPLE SUMMARY: Total neoadjuvant therapy is a strategy developed to improve the efficacy of chemotherapy in locally advanced rectal cancer by anticipating all the chemotherapy before surgery. This improves compliance, early exposure to micrometastatic disease, and local tumor response. In two recent randomized studies, the rates of patients developing distant metastases were indeed reduced, and the proportions of patients showing complete tumor regression at surgery doubled with two different regimens of total neoadjuvant treatment compared to preoperative long-course chemoradiation. Other studies showed that this strategy facilitates rectal preservation with increased rates of clinically complete tumor disappearance without surgery. However, the optimal chemotherapy regimen, radiotherapy schedule, and timing of chemotherapy and radiotherapy are yet to be defined and may not be the same for all risk groups. Additionally, TNT may result in overtreatment for low-risk patients. Indications for this strategy and specific TNT regimens should thus be adapted to different clinical scenarios. ABSTRACT: Many consider the standard of care for locally advanced rectal cancer (LARC) to be preoperative chemoradiotherapy, radical surgery involving a total mesorectal excision, and post-operative adjuvant chemotherapy based on the pathology of the specimen. The poor impact on distant control is a major limitation of this strategy, with metastasis rates remaining in the 25–35% range and recovery after radical surgery leading to reluctance with prescription and inconsistent patient compliance with adjuvant chemotherapy. A second limitation is the low rate of pathologic complete response (pCR) (around 10–15%) despite multiple efforts to potentiate preoperative chemoradiation regimens, which in turn means it is less effective at achieving non-operative management (NOM). Total neoadjuvant treatment (TNT) is a pragmatic approach to solving these problems by introducing systemic chemotherapy at an early timepoint. Enthusiasm for delivering TNT for patients with LARC is increasing in light of the results of published randomized phase III trials, which show a doubling of the pCR rate and a significant reduction in the risk of subsequent metastases. However, there has been no demonstrated improvement in quality of life or overall survival. A plethora of potential chemotherapy schedules are available around the radiotherapy component, which include preoperative induction or consolidation with a range of options (FOLFOXIRI, FOLFOX, or CAPEOX,) and a varying duration of 6–18 weeks, prior to long course chemoradiation (LCCRT) or consolidation NACT following short-course preoperative radiation therapy (SCPRT) using 5 × 5 Gy or LCCRT using 45–60 Gy, respectively. The need to maintain optimal local control is a further important factor, and preliminary data appear to indicate that the RT schedule remains a crucial issue, especially in more advanced tumors, i.e., mesorectal fascia (MRF) invasion. Thus, there is no consensus as to the optimum combination, sequence, or duration of TNT. The selection of patients most likely to benefit is challenging, as clear-cut criteria to individuate patients benefiting from TNT are lacking. In this narrative review, we examine if there are any necessary or sufficient criteria for the use of TNT. We explore potential selection for the individual and their concerns with a generalized use of this strategy.