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Lymphatic mapping with sentinel lymphadenectomy is undoubtedly one of the most interesting developments in oncology today. Use of this minimally invasive procedure can document regional lymph node involvement with a high degree of accuracy. The concept is appealing because it is so simple and logical. In addition, it apparently is applicable to a range of neoplastic diseases, including melanoma, breast cancer, carcinoma of the vulva, carcinoma of the penis, and possibly other types of cancer as well.

The underlying hypothesis goes back a long way. The pioneering surgeon William S. Halsted (1852-1922) proposed that lymph nodes were a barrier to the spread of tumor cells, that lymphatic dissemination of neoplasms progressed in an orderly fashion, and that lymph nodes were a source of distant spread of tumor cells. Over the years ideas have changed, and during most of the latter half of the twentieth century the general opinion was the opposite. Only a few individuals had the vision and courage to challenge the widely held view that Halstedian thinking was obsolete.

R. S. Cabanas, a resident in urology at the Memorial Sloan-Kettering Cancer Center in New York, initially used the term ''sentinel node.'' In 1977, he suggested that squamous cell carcinoma of the penis initially drained to a particular lymph node in the groin that was always in the same position. For penile cancer this appeared to make some sense, because penile cancer is always located in exactly the same part of the body, unlike melanoma or even breast cancer. Cabanas called that node the ''sentinel'' node.

However, it was D. L. Morton and A. J. Cochran, at the John Wayne Cancer Institute at Saint John's Health Center in Santa Monica and UCLA, respectively, who developed the concepts of lymphatic mapping and selective lymph node biopsy for melanoma. They reasoned that any node in a particular lymphatic field could be the sentinel node, depending on the location of the primary melanoma and with a certain individual variability.

It is not surprising that Morton played a key role in the inception of lymphatic mapping because he was one of the early proponents of lymphoscintigra-phy, and lymphoscintigraphy is a cornerstone of lymphatic mapping. Being a melanoma surgeon, Morton was also wrestling with the question of whether or not to perform elective lymph node dissection, a controversial procedure in that disease. In retrospect, it is understandable that treatment of melanoma was the breeding ground for lymphatic mapping and that Morton was its initiator.

The original definition of a sentinel node has recently become a source of some confusion. Morton stated that a sentinel node is the initial lymph node into which the primary tumor drains. In other words, the sentinel node (first-tier node, first-echelon node) is the lymph node on the direct drainage pathway from the primary tumor. Some investigators have altered this definition and come up with their own interpretations. This is understandable, because everybody is looking at this development from his or her own background and perspective. For instance, some investigators in the field of nuclear medicine define the sentinel node as the first lymph node that becomes visible on the lymphoscintigraphy images. Although there is some truth in that definition, because the first node that lights up is a sentinel node, this definition does not acknowledge the fact that there may be more than just one sentinel node. Sometimes there are two lymphatic ducts draining the primary tumor, running to two different lymph nodes in the same basin. Because of a preferential flow, one node may appear on the scintigraphy images earlier than the other, but that does not mean that only the first node is a sentinel node. Tumor cells can travel through either duct and lodge in either node. There may even be more than two sentinel nodes. All these firsttier nodes should be collected by the surgeon and examined by the pathologist. Therefore, this particular definition is too narrow: too few nodes are labeled sentinel node and metastases may be missed.

Other investigators define a sentinel node as either a blue node or a radioactive node. In their opinion, every blue node or radioactive node is a sentinel node. These investigators do not acknowledge the fact that some of the tracer may pass through the first-tier lymph node and lodge in secondary nodes that are not directly at risk of harboring metastatic disease. Thus, this definition is too broad and too many nodes may be removed. In this book we adhere to Morton's original definition to avoid confusion.

Lymphatic Mapping and Probe Applications in Oncology had its inception in the work of B. A. E. Kapteijn at The Netherlands Cancer Institute. She studied various aspects of lymphatic mapping and her findings were reported in a Ph.D. thesis. Her work with its basic information was in such demand that the book was reprinted twice. The apparent interest in the subject prompted Marcel Dek-ker, Inc., to encourage us to produce the present volume. The feeling proved to be correct because interest in lymphatic mapping continues to grow at a rapid pace, and the number of publications on the subject is increasing exponentially. Lymphatic mapping is the hot topic at many national and international conferences in various fields of medicine. Training courses are frequently oversubscribed. Despite the lack of firm proof from randomized trials that lymphatic mapping is beneficial, one thing is now crystal clear: this development cannot be stopped! These techniques will be incorporated into routine patient care. There is a great demand for information. Lymphatic Mapping was produced to fill this need by providing a comprehensive review of the current state of the art.

The sentinel node is identified through elegant applications of techniques that visualize a physiological process. Chapter 1 describes the relevant microanatomy and physiology of the lymphatic system, and Chapter 2 presents the history of lymphatic mapping. Lymphatic mapping is the work of a multidiscipli-nary team. It cannot be overstated how important it is for the surgeon (or gynecologist or urologist) to have adequate nuclear medicine support. This is lymphatic mapping. The nuclear medicine physician provides the road map that guides the surgeon. Chapters 2, 3, and 9 present various aspects of lymphoscintigraphy. The surgical technique is described in Chapter 4. Important features of gamma-ray detectors are discussed in Chapter 5. The current status of knowledge of lymphatic mapping in melanoma is described in Chapter 6. The pathologist is an important member of the lymphatic mapping team, and Chapters 7 and 8 discuss the pathological evaluation of a sentinel node. Chapter 10 deals with breast cancer, Chapter 11 with carcinoma of the vulva, and Chapter 12 with carcinoma of the penis. Chapter 13 deals with radiation protection issues related to the sentinel node procedure. Chapter 14 provides practical information for doctors who intend to implement lymphatic mapping in their hospital. A gamma-ray detection probe can be used for other purposes in addition to lymphatic mapping. These applications are described in Chapters 15, 16, and 17. Practical information on lymphatic mapping can be gathered from the case reports presented in Chapter 18. Chapter 19 speculates about the future role of this procedure. All chapters were written to be understandable to all members of the team. Statements are illustrated by clinical examples where useful. We have endeavored to point out where controversy exists and to present evidence where it exists. We hope that this book will provide practical information for those who intend to include this procedure in their clinical armamentarium.

Omgo E. Nieweg Richard Essner Douglas S. Reintgen John F. Thompson

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