Assessment of lymph node involvement in colorectal cancer

Abstract

Lymph node metastasis informs prognosis and is a key factor in deciding further management, particularly adjuvant chemotherapy. It is core to all contemporary staging systems, including the widely used tumor node metastasis staging system. Patients with node-negative disease have 5-year survival rates of 70%-80%, implying a significant minority of patients with occult lymph node metastases will succumb to disease recurrence. Enhanced staging techniques may help to identify this subset of patients, who might benefit from further treatment. Obtaining adequate numbers of lymph nodes is essential for accurate staging. Lymph node yields are affected by numerous factors, many inherent to the patient and the tumour, but others related to surgical and histopathological practice. Good lymph node recovery relies on close collaboration between surgeon and pathologist. The optimal extent of surgical resection remains a subject of debate. Extended lymphadenectomy, extra-mesenteric lymph node dissection, high arterial ligation and complete mesocolic excision are amongst the surgical techniques with plausible oncological bases, but which are not supported by the highest levels of evidence. With further development and refinement, intra-operative lymphatic mapping and sentinel lymph node biopsy may provide a guide to the optimum extent of lymphadenectomy, but in its present form, it is beset by false negatives, skip lesions and failures to identify a sentinel node. Once resected, histopathological assessment of the surgical specimen can be improved by thorough dissection techniques, step-sectioning of tissue blocks and immunohistochemistry. More recently, molecular methods have been employed. In this review, we consider the numerous factors that affect lymph node yields, including the impact of the surgical and histopathological techniques. Potential future strategies, including the use of evolving technologies, are also discussed.

Keywords: Colorectal cancer; Lymphatic metastases; Lymph node metastasis; Neoplasm staging; Tumor node metastasis classification; Sentinel lymph node biopsy; Lymph node excision; Histopathological assessment; Surgery

Core tip: The number of lymph nodes in surgical resection specimens is influenced by numerous factors. Good practice by surgeons and pathologists is essential to maximize lymph node yields, but there are non-modifiable factors related to patient and tumour. Extended lymphadenectomy, extra-mesenteric lymph node dissection, high arterial ligation and complete mesocolic excision, all increase lymph node yields, but a definite benefit in prognosis is not proven and the optimal extent of surgical resection remains contentious. Conversely, further development in sentinel lymph node biopsy techniques could allow selective lymphadenectomy, whilst providing appropriate information to guide adjuvant therapy.