Wang Yi, Chen Gong
Department of Radiology, Peking University People's Hospital, Beijing 100044, China.
Department of Colorectal Surgery, Sun Yat-sen University Cancer Center, Guangzhou 510060, China.
Zhonghua Wei Chang Wai Ke Za Zhi. 2017 Jun 25;20(6):630-634.
The primary curative modality for localized rectal cancer is total mesorectal excision (TME). Local control rate of rectal cancer has been improved after neoadjuvant chemoradiotherapy and even pathological complete response (pCR) has been demonstrated in a significant minority. Patients who achieve pCR to neoadjuvant chemoradiotherapy have an excellent prognosis compared with those without pCR. If the patients with complete response to neoadjuvant chemoradiation can be demonstrated by clinical findings and medical imaging (cCR), a non-operative management (NOM) strategy may be pursued to preserve sphincter function and avoid complications induced by TME, which is a new tendency in the treatment of rectal cancer in recent years. Assisting diagnosis of cCR by iconography is the important element of NOM practice. Selected patients should be followed up with intensive surveillance. The curative strategy must be carried out once the recurrence is detected. Imaging modalities, including magnetic resonance imaging (MRI), diffusion-weighted MRI, or proton emission tomography (PET), are limited in their ability to distinguish patients who have achieved cCR. Up to now, MRI, DW-MRI and 18F-FDG PET/CT before neoadjuvant chemoradiotherapy are not accurate enough to predict cCR and safely select patients for organ-sparing strategies. However, depth of tumor infiltration, extramural vascular invasion, circumferential resection margin, and location of rectal cancer can be demonstrated by high resolution MRI as independent risk factors in prediction of long-term survival of patients, which is a necessary manner of stratification treatment for rectal cancer. Therefore, patients who are defined as early rectal cancer with low risk factors are selected as candidates for NOM in recent studies in order to pursue low rate of local recurrence and distant metastasis. High resolution MRI assessment of tumor regression grade (mrTRG) can be used to assess response of rectal cancer to neoadjuvant chemoradiotherapy, which is associated with tumor burden. mrTRG is an imaging marker that indicates the difference in survival between good and poor responders and provides an opportunity for the multidisciplinary team to offer additional treatment options before planning definitive surgery. Functional imaging and even molecular imaging are needed in the future to screen suitable rectal cancer patients who are easier to achieve cCR from neoadjuvant chemoradiotherapy and to evaluate the efficacy of neoadjuvant chemoradiotherapy.
局部直肠癌的主要治疗方式是全直肠系膜切除术（TME）。新辅助放化疗后直肠癌的局部控制率有所提高，甚至有相当一部分患者实现了病理完全缓解（pCR）。与未实现pCR的患者相比，新辅助放化疗达到pCR的患者预后良好。如果通过临床检查和医学影像（cCR）能够证实患者对新辅助放化疗完全缓解，可采用非手术治疗（NOM）策略来保留括约肌功能并避免TME引起的并发症，这是近年来直肠癌治疗的新趋势。通过影像学辅助诊断cCR是NOM实践的重要环节。选定的患者应进行密切随访。一旦检测到复发，必须实施治疗策略。包括磁共振成像（MRI）、扩散加权MRI或正电子发射断层扫描（PET）在内的成像方式在区分实现cCR的患者方面能力有限。到目前为止，新辅助放化疗前的MRI、DW-MRI和18F-FDG PET/CT在预测cCR和安全选择适合保留器官策略的患者方面不够准确。然而，高分辨率MRI可以显示肿瘤浸润深度、壁外血管侵犯、环周切缘以及直肠癌的位置，这些是预测患者长期生存的独立危险因素，这是直肠癌分层治疗的必要方式。因此，在最近的研究中，被定义为具有低风险因素的早期直肠癌患者被选为NOM的候选者，以追求低局部复发率和远处转移率。高分辨率MRI评估肿瘤退缩分级（mrTRG）可用于评估直肠癌对新辅助放化疗的反应，这与肿瘤负荷相关。mrTRG是一种成像标志物，可以显示反应良好和反应不佳者之间的生存差异，并为多学科团队在规划确定性手术前提供额外的治疗选择机会。未来需要功能成像甚至分子成像来筛选更容易从新辅助放化疗中实现cCR的合适直肠癌患者，并评估新辅助放化疗的疗效。
