Detection of occult metastases of mammary carcinomas in lymph nodes of dogs by immunohistochemistry combined with histochemistry techniques
Authors: Barraza Vanessa C.T. , Buttelli Pedro Henrique S. , Vargas Indianara de , Goldani Mariana A. , Medeiros Alice M. de , Sangoi Flávia A. , Flores Mariana M. , Kommers Glaucia D. 
Published: September 2024

ABSTRACT: Lymph node status is considered an important clinical prognostic factor in canine mammary carcinomas and women’s breast neoplasms. However, occult isolated tumor cells (ITCs) can be missed during hematoxylin and eosin (HE) analyses. Immunohistochemistry (IHC) for cytokeratin can be used to detect carcinomatous occult ITCs in mammary drainage lymph nodes. However, brown pigments, such as hemosiderin and ceroid in lymph nodes, may hinder the search for occult metastases by IHC utilizing DAB (3,3′-diaminobenzidine) as the chromogen. The aim of this study was to identify ITCs in canine lymph nodes of cases in which it was not detectable by routine HE evaluation through IHC for cytokeratin (AE1/AE3) combined with histochemistry techniques, such as Perls’ Prussian blue and periodic acid-Schiff (PAS), to improve the detection of occult metastases when hemosiderin and ceroid were present in these lymph nodes. For this, 25 tubulopapillary mammary carcinomas with their respective submitted 29 regional lymph nodes, previously given as free of tumor cells by HE analyses, were selected. Mammary tumors were graduated, and vascular invasion was investigated in these tumors. The submitted lymph nodes were reevaluated in HE, looking for occult metastases. IHC for cytokeratin (AE1/AE3) was used to detect occult metastases in mammary lymph nodes. Subsequently, a combined technique of IHC with Perl’s Prussian blue (for hemosiderin) or PAS (for ceroid) was performed to optimize the detection of ITCs by IHC, distinguishing them from pigments. Occult metastases were classified by their microanatomical location in subcapsular, cortical and medullary. Hemosiderin and ceroid were searched in lymph nodes and quantified as low, moderate, or high. The amount of pigments with a percentage of ITCs was also compared. Isolated tumor cells were found in 24.1% (7/29) of mammary lymph nodes. These ITCs were located mainly in subcapsular sinuses (4/7; 57.1%), followed by cortical (2/7; 28.5%) and medullary sinuses (1/7; 14.3%). There were concomitant lymph nodes with ITCs in 33.4% (2/6) of cases with vascular invasion. Hemosiderin and ceroid were present in about 90% of the 29 lymph nodes analyzed. In 42.8% (3/7) of lymph nodes with ITCs, hemosiderin and/or ceroid were in the same location as ITCs. It was found that lymph nodes in which ITCs were detected also present high amounts of hemosiderin (3/7; 42.9%) and low amounts of ceroid (5/7; 71.4%). In this study, IHC for cytokeratin (AE1/AE3) was an efficient method to detect occult tumor cells. IHC combined with Perls’ Prussian blue or with PAS proved to be a helpful way to investigate the presence of occult metastases in the lymph nodes of mammary canine tumors. It allowed distinguishing hemosiderin and ceroid, respectively, from ITCs in the same slide of IHC (immunostained by DAB), favoring a more accurate analysis by pathologists, which can be useful for the oncological staging of these patients.