Identification of occult micrometastases and isolated tumour cells within regional lymph nodes of previously diagnosed non-metastatic (stage 0) canine carcinomas

Metastatic dissemination of carcinomas to lymph nodes impacts prognosis and treatment recommendations in human and veterinary medicine. Routine histopathologic evaluation of regional lymph nodes involves haematoxylin and eosin (HE however, identification of small volume metastases (micrometastases and individual tumour cells) may be missed without the aid of immunohistochemistry or additional step-sections. The aim of this study was to identify occult carcinoma metastases in previously diagnosed non-metastatic lymph nodes using step-sections and pancytokeratin (panCK) immunohistochemistry. Samples from 20 regional lymph nodes diagnosed as non-metastatic were serially sectioned and evaluated with panCK. Of these, 25% (n = 5) contained micrometastases (n = 1) or isolated tumour cells (n = 4). This study demonstrates the increased efficacy of serial step-sections combined with panCK immunohistochemistry to identify small volume metastases in regional lymph nodes. The prognostic significance of micrometastases and isolated tumour cells in regional lymph nodes warrants further investigation in veterinary medicine.