Sentinel Lymph Node Biopsy
As noted above, the standard pathologic practice for the evaluation of nonsentinel lymph nodes is to examine microscopically one section from each lymph node using the simple H&E technique. Although this approach may be practical for evaluating large numbers of lymph nodes, most pathologists would concede that such limited analysis consistently underestimates the true in-cidence of occult nodal metastases. Recent im-provements in our clinical ability to identify the lymph nodes most likely to harbor metastases have facilitated the accurate staging of cancers. The sentinel lymph node strategy is particularly appealing because the surgical removal of just one or several selected lymph nodes permits a more comprehensive pathologic search for small and localized metastatic deposits.
Methods for detecting tumor cells in sentinel lymph nodes have become increasingly sophis-ticated and sensitive, ranging from routine histologic examination of serial sections to re-verse transcriptase-polymerase chain reaction-based methods for detecting a single tumor cell among a sea of lymphocytes. Outside of routine H&E staining, however, most detection methods are investigational, and currently there is no agreement as to an optimal detection protocol. Given the diversity of the processing and exami-nation of sentinel lymph node biopsies among laboratories, you should be familiar with the protocol details specific to your own institution. At the same time, there are generic guidelines that are widely applicable across institutions and assorted tumor types.
The sentinel lymph node biopsy specimen should be carefully examined to determine the number of lymph nodes. The size of each should be recorded. Each lymph node should be pro-cessed separately. Each node is serially sectioned along the longitudinal or transverse plane into 3- to 4-mm slices. Small lymph nodes that can-not be easily sectioned should be submitted in toto. Examine the cut surface of each slice for the presence of grossly visible tumor nodules.
Your gross assessment of the lymph node dic-tates the degree of sectioning by the histopathol-ogy laboratory. If tumor is visualized grossly, routine H&E staining of a single level is sufficient to document the presence of tumor and its possi-ble extension beyond the lymph node capsule. If tumor is not grossly visible, the lymph node slices should be sectioned at multiple levels. There is currently no standard to guide the ex-tent of tissue sectioning. At a minimum, one section from each of three levels of the tissue block should be obtained for routine H&E staining.Regardless of whether immunohisto-chemistry is part of a specific protocol, the his-topathology laboratory should place intervening unstained sections on sialinated slides in an effort to minimize loss of potentially diagnostic material and provide a source of unstained sections should the need for immunohisto-chemistry arise.
The process of clinical lymphatic mapping and the identification of sentinel lymph nodes relies on nodal uptake of radioactive tracers. Fortunately for pathology personnel, the amount of radiation associated with sentinel lymphadenectomies is low. Even with frequent handling of these speci-mens, radiation exposure usually does not ap-proach statutory exposure limits. Given the exceedingly low radiation exposure, most au-thorities now agree that quarantining these specimens does not enhance the safety of pathol-ogy personnel and only serves to delay the final diagnosis. Accordingly, sentinel lymph node biopsies should be processed immediately on re-ceipt from the operating room using customary universal precautions. Nonetheless, if you have a question about a particular specimen, you should call your institution’s radiation safety officer.
1. Record the number of lymph nodes and their dimensions.
2. Serial section each lymph node along its longitu-dinal or transverse plane into 3- to 4-mm slices.
3. If a metastatic implant is grossly visible, have the histopathology laboratory cut and stain one representative section to document the presence of tumor.
4. If a metastatic implant is not grossly visible, have the histopathology laboratory cut multi-ple sections from at least three levels. At least one section from each level should be stained with H&E. Additional unstained sections should be stored on treated slides for future immunohistochemical studies as needed.
· What procedure was performed?
· How many lymph nodes from each anatomic level harbor metastatic tumor, and how many lymph nodes from each level were microscopi-cally examined?
· What is the size of the largest metastatic implant?
· Does the metastasis extend beyond the nodal capsule into the surrounding perinodal fat? (This is particularly important to note for meta-static squamous cell carcinomas of the head and neck and metastatic carcinomas of the breast.)
· For sentinel lymph node biopsies, was the metastasis detected by routine histopathol-ogy, immunohistochemistry, molecular-genetic analysis, or some combination of these tech-niques?
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