The Fine Structure and Function of the Lymphatic Vascular System

Lymphatic Mapping and Sentinel Lymph Node Biopsy

The status of the regional nodal basin remains the most important prognostic indicator of survival. The current standard of care for the management of invasive breast cancer is the complete removal of the tumor, with documentation of negative margins by either mastectomy or lumpectomy, followed by complete axillary lymph node dissection. Data suggest that complete lymph node dissection (CLND) provides better local control of the disease and may actually offer a survival advantage. Lymphatic mapping and sentinel lymph node (SLN) biopsy are clearly changing this long-held paradigm and have the potential to change the standard of surgical care of the breast cancer patient. The purpose of this report is to describe the lymphatic mapping experience at the H. Lee Moffitt Cancer Center and Research Institute. From April 1994 to January 1999, 1,147 consecutive breast cancer patients were enrolled in an institutional review board-approved lymphatic mapping protocol. Lymphatic mapping was performed using Tc99m-labeled sulfur colloid and isosulfan blue dye. An SLN was defined as any blue node and/or any hot node with ex vivo radioactivity counts >/=10 times an excised non-SLN or in situ radioactivity counts >/=3 times the background counts. Lymphatic mapping was successful in identifying the SLN in 1,098 of 1,147 (95.7%) cases. In the first 186 patients, all of whom underwent CLND following SLN biopsy, one false-negative biopsy was encountered for a false-negative rate of 0.83%. The method of diagnosis (excisional versus minimally invasive) does not appear to impact on lymphatic mapping. Tumor size, however, is directly related to the probability of axillary lymph node involvement. Advances in technology and the development of minimally invasive surgical techniques have heralded a new era in surgery. Lymphatic mapping and SLN biopsy may actually prove to be a more accurate method of identifying metastases to the axilla by allowing a more focused pathologic examination of the axillary node(s) at highest risk for metastasis. With adequate training, this technique can be readily implemented as a valuable tool in the surgical treatment of breast cancer.

The role of selective sentinel lymph node dissection in breast cancer

Axillary nodal status continues to be the most statistically significant predictor of survival for patients with breast cancer. Although still providing regional control of axillary disease, axillary dissection is more important as a staging and prognostic tool. Trials are currently underway to investigate the possibility of replacing the current standard treatment of breast cancer, axillary lymph node dissection, with the less invasive lymphatic mapping and sentinel lymph node biopsy. This issue and the technical aspects of sentinel lymph node mapping for breast cancer are discussed in detail in this article.

Lymphatic mapping and sentinel lymph node biopsy in patients with breast cancer

The standard of care for the evaluation of axillary nodal involvement remains complete lymph node dissection. Lymphatic mapping and sentinel lymph node (SLN) biopsy are changing this long-held paradigm; indeed, several leading institutions already reserve complete axillary dissection for patients with metastasis to the SLN. In addition to reviewing the literature, this chapter describes our lymphatic mapping experience at the H Lee Moffitt Cancer Center and Research Institute with 1147 breast cancer patients. Our results, in addition to a meta-analysis of data from 12 institutions comprising an additional 1842 patients undergoing complete axillary dissection, demonstrate that SLN biopsy is an accurate method of axillary staging. Although the results from small series may exaggerate the probability of false negative results, the risk of nodal disease based on tumor size and other risk factors should be evaluated when considering the results of SLN sampling.

Structure and function of lymphatics

Lymphatics are large vessels with a lumen potentially ten times wider than blood vessels and have a mean mesh diameter in the upper dermis of approximately 504 +/- 88 microns. The plexus lies just deep to the subpapillary venous plexus and when functioning well it is difficult to identify because of the attenuated endothelium and collapsed lumen. The role of the lymphatic as a pathway for the Langerhans cell and as an exit for macromolecules such as lipid and protein make it an essential organ for normal skin biology. When this system fails, impaired immunity, fibrosis, and recurrent infections are inevitable. Even vasculitis may be a consequence of failure of clearance of immune complexes from the interstitium. The adipose tissue and deep dermis are especially vulnerable in this respect. Elastin fibers support cutaneous lymphatics and may be low resistance pathways through the connective tissues into the lymphatic. Identification of lymphatics by special markers is a concept that currently fails to take into account that changing roles in disease may be associated with a change in the specificity of markers. The anatomy of lymphatic vessels in the skin is described and the role of the lymphatic is emphasized.