
Lymph nodes are essential components of the lymphatic system, playing a vital role in immune surveillance and the body’s response to cancer. In surgical oncology, the examination of lymph nodes is of great importance for various aspects of cancer management; from diagnosis and staging to treatment planning, and prognosis.
Tumour staging is critical for predicting prognosis and guiding clinicians in treatment decision-making. Lymph nodes are often the first sites of metastasis from primary tumours due to their role in filtering lymphatic fluid, making them a significant barrier to the spread of cancer cells. The assessment of lymph nodes is essential in the staging of various cancers because the presence of metastatic spread in lymph nodes is a key factor in determining the stage of the disease. Given that lymph node palpation has limited value in predicting lymph node metastasis, that cytology can result in false positives and negatives and that not all regional lymph nodes are accessible for immediate fine-needle aspiration due to their anatomical location or size, histopathology is increasingly being considered for diagnosing lymph node metastasis. The extirpation of non-palpable or normal-sized lymph nodes can permit early detection of nodal metastasis and more accurate tumour staging in several cancers in dogs and cats such as mammary carcinoma, anal sac adenocarcinoma, mast cell tumours, melanoma, and pulmonary carcinoma.
In addition, the growing awareness of the possible prognostic and therapeutic implications of micrometastases has increased the recommendation for surgical removal of normal-sized draining lymph nodes for histologic staging. The involvement of lymph nodes significantly guides treatment plans and aids in decision making, including the need of adjuvant chemotherapy, radiotherapy (of the lymph node bed), and extensive surgical interventions. In some cancers, such as mast cell tumours and anal sac adenocarcinomas, lymphadenectomy can be therapeutic, helping to reduce disease burden and improve patient outcomes.
Recent studies have focused on the molecular signals and cellular changes involved in lymph node metastasis. Key changes include lymphangiogenesis, the expansion of immunosuppressive cells, up-regulation of chemokines and cytokines, and blood vessel remodelling in the lymph node. These processes facilitate tumour cell entry, colonisation, and survival within the lymph node. Understanding these mechanisms could be important for developing targeted therapies and improving cancer treatment outcomes also in veterinary medicine.
Despite these apparent benefits, the decision to perform lymphadenectomy in cancer treatment is complex and influenced by various factors that should be analysed for each individual patient. Key considerations include the incidence of lymph node metastasis for the particular tumour, risk factors for lymph node involvement (such as larger tumour size and presence or abscence of lymphovascular invasion on histopathology), and the effect of lymph node metastasis on prognosis.
Risks and complications associated with lymphadenectomy, particularly for intra-abdominal and pelvic lymphadenectomy should also be taken into consideration. These procedures can carry significant risks of complications, making it essential to weigh the benefits against the potential harm to the patient.
Other challenges and limitations that should be taken into consideration when interpreting lymph node status include the unpredictable behaviour of some cancers; where distant metastasis can be seen before lymph node involvement. Conversely, large invasive tumours may not develop lymph node metastasis. This variability complicates the decision to perform lymphadenectomy, as it may not always correlate with disease progression. Furthermore, the more lymph nodes removed, the more metastasis or micrometastasis may be detected. However, this leads to questions about the utility of this information in cancers where the impact on outcomes or whether treatment will prolong survival remains uncertain.
In conclusion, lymph node evaluation is a cornerstone of oncologic management, providing critical insights into the staging, prognosis, and treatment of cancer. The detection and removal of metastatic lymph nodes for some tumours play a pivotal role in improving patient outcomes. Despite the advancements, challenges and controversies remain in lymph node assessment and the decision to perform lymphadenectomy. The variability in lymph node involvement and the potential risks associated with the procedure necessitate a careful, individualised approach to each patient. As research advances, a better understanding and guidelines will help refine these decisions, ultimately improving patient outcomes in both human and veterinary medicine.