Today's Veterinary Practice

MAY-JUN 2014

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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tvpjournal.com Today's Veterinary Practice May/June 2014 18 A t the time of cancer diagnosis, the clinician's first task is to determine disease extent within the body, that is, to stage the cancer. Stage describes the extent of the tumor, lymph node involvement, and spread of disease, measuring the scope of metastasis. Grade describes the appearance of the cells upon histopathology. Higher grade tumors are more likely to present at a higher stage. Staging is performed by the cli- nician, whereas grading is performed by the pathologist. With practice, enough information can be gained from lymph node cytology to allow the general practitioner to begin a dialogue with pet owners about concern for meta- static cancer and its impact on prognosis. This article reviews normal and abnormal lymph node cytology in both solid and round/discrete cell (hemolym- phatic) tumors from the perspective of an oncologist. ROUTES OF METASTASIS Cancer can metastasize via lymphatics or blood vessels (hematogenously): • Mesenchymal tumors (sarcomas) predominantly metastasize via blood vessels , but can occasionally travel by lymphatics, which is typically a sign of more aggressive disease—one that metastasizes more readily, resulting in shorter survival times. • Epithelial (carcinomas) and round/discrete cell tumors metastasize via lymphatics more often than mesenchymal tumors. Regardless of tumor type, regional lymph node cytology should be included in the first wave of diagnostics for most cancers. LYMPH NODES TO SAMPLE While metastasis to an unexpected lymph node is always possible, the important lymph nodes to aspirate at time of staging are: • The primary draining lymph node • Any enlarged lymph nodes (even if distant from the pri- mary tumor). For several tumors, including melanoma and mast cell tumor, metastasis can be identified even if lymph nodes are of normal size. 1 In addition to screening for metastasis of solid tumors, lymphoma is often easily diagnosed using lymph node aspiration and cytology. FINE-NEEDLE ASPIRATION Location Considerations When evaluating metastatic solid tumors, the prima- ry draining lymph node that should be sampled depends upon location (eg, popliteal node for a hind foot digital tumor). Tumors located in areas of the body where lymphat- ic drainage is not clear, such as on the lateral thorax, can be challenging. In this situation, the nearest major lymph node should be aspirated if it can be isolated, though at times this is not possible and lymph nodes are noted as within normal limits without cytologic interpretation. When diagnosing lymphoma, the popliteal lymph nodes are the most accessible lymph nodes, followed by the pre- scapular nodes. Mandibular lymph nodes should be avoided if other nodes are enlarged, because reactive lymphoid cells (due to changes in the ears or mouth) may cloud a diagnosis of lymphoma. However, if the mandibular nodes are the only enlarged lymph nodes, they should be aspirated. A cytolog- ic diagnosis of reactive or equivocal lymph node should be interpreted with caution: if lymphoma is suspected, further testing, such as biopsy, should be pursued if suspicion is high. Isolation of Node When isolating a lymph node: 1. Place the forefingers in an anatomic location just beyond the node. 2. Use the thumb to isolate and steady the node. For example, to isolate the prescapular/superficial cervi- cal node: 1. Place the fingers in, or just above, the thoracic inlet. 2. Sweep the thumb down the front of the shoulder where the supraspinatus muscles meet the neck muscles. Peer reviewed In one large case series of dogs with osteosarcoma, incidence of lymph node metastasis was only 4%, but the median disease-free interval was only 48 days in dogs with "positive" lymph nodes compared with 238 days for dogs with unaffected lymph nodes. 2 LYMPH NODE CYTOLOgY What Should & Should Not Be There LYMPH NODE CYTOLOgY What Should & Should Not Be There Kim A. Selting, DVM, MS, Diplomate ACVIM (Oncology) & ACVR (Radiation Oncology) University of Missouri Kim A. Selting, DVM, MS, Diplomate ACVIM (Oncology) & ACVR (Radiation Oncology) University of Missouri TVP_2014-0506_Lymph Node Cytology.indd 18 5/24/2014 10:38:59 AM

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