Preoperative staging and outcome following surgical and local resection of T1 colorectal cancer

Background: There are two conceptually different surgical treatment options for patients with T1 colorectal cancer (CRC): radical surgical resection and local resection. In addition, adjuvant chemotherapy is recommended in cases with lymph node metastases. However, surgical overtreatment of early CRC is a concern and may be related to limitations in preoperative work-up as well as tumour risk classification. In addition, patients with node-positive T1 CRC disease may be undertreated with respect to adjuvant chemotherapy.Aims: Study I: To assess the accuracy of MRI-based staging in early rectal cancer (RC). Study II: Compare recurrence after endoscopic and surgical resection across risk groups in pT1 colon cancer (CC) and identify risk factors for recurrence. Study III: Compare recurrence after transanal endoscopic microsurgery (TEM) and surgical resection across risk groups in pT1 RC. Study IV: Investigate the effect of adjuvant chemotherapy on recurrence and survival in pT1 node-positive (T1N+) CRC and identify factors associated with not receiving adjuvant chemotherapy.Methods: The four studies were retrospective cohort studies based on prospectively collected data derived from the Swedish Colorectal Cancer Registry. Study I, patients with RC staged as cT1–2 RC or pT1 (2009–2018), Study II patients with pT1 CC (2009– march 2021), Study III patients with pT1 RC (2009–2022), Study IV pT1 N+ CRC (2009–2022). Neoadjuvant treatment was a general exclusion criterion for all studies.Results and conclusions: Study I. MRI plays a pivotal role in the work-up of RC. However, MRI was insufficiently accurate for both T and N staging in early RC, with a risk of both over- and understaging. Based on these findings, MRI should not be used as the sole modality to determine eligibility for local resection. Study II. Recurrence rates after pT1 CC were low and comparable following endoscopic and surgical resection, even in patients with high-risk tumours. Lymphovascular invasion (LVI) was identified as a strong risk factor for recurrence. Further studies to identify pT1 CC patients with poor prognosis who may benefit from additional treatment are warranted. Study III. In contrast, local recurrence rates following TEM were significantly higher than those after surgical resection, even in patients with low-risk tumours, calling into question the role of TEM as a curative treatment option. Study IV. Adjuvant chemotherapy was associated with substantially improved disease-free and overall survival in patients with pT1N+ CRC, highlighting the importance of minimizing unfounded deviations from treatment guidelines.