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EDITORIALS |
From the Department of Obstetrics & Gynecology, University of Texas, Southwestern Medical Center, Dallas, Texas.
Correspondence: Address correspondence to: Robert L. Coleman, MD, Department of Obstetrics & Gynecology, University of Texas, Southwestern Medical Center, 5323 Harry Hines Blvd., J7.124, Dallas, TX 75390-9032; Fax: 214-648-8404; E-mail: Robert.coleman{at}utsouthwestern.edu
Over the last 50 years, refinement in the management of vulvar carcinoma has progressed methodically through alterations in surgical radicality, incorporation of adjuvants (chemotherapy and radiation), and patient selection for the use of these modalities. Our challenge to the "Halsteadian" approach of oncologic surgery in the vulva has proceeded cautiously as that model proved efficacious for survival, albeit, often at the cost of lasting morbidity. The application of lymphatic mapping and sentinel node identification represents another tempting step in this process; the "carrot" being the promise of improved nodal precision and reduced morbidity. Examination of our past in this regard shows that the "carrot" is indeed enticing.
Although cutaneous melanoma is an uncommon malignancy of the vulvar epithelium, its occurrence is enigmatic as our knowledge of the natural history and appropriate definitive treatment is lacking. Reviews from retrospective studies have been inconclusive and adaptation of the management from other cutaneous sites has dictated treatment strategy. Therefore, wide radical excision (up to 5 cm of normal appearing skin) of the local site or radical vulvectomy and inguinal-femoral lymphadenectomy has been the dictum of treatment. Recent experience, however, has called into question the necessity of both the degree of radicality at the primary site and the completeness of nodal dissection necessary to obtain what appears to be only prognostic information from the regional drainage basins.1–3 Although more typical circumferential margins (1–2 cm) are replacing the radical approach locally, the decision of whether to complete full lymphadenectomy is often left to imprecisely known preoperative factors, such as tumor thickness and capillary space invasion. Adaptation of sentinel node identification techniques intuitively, and if validated, represents a clear compromise between the knowledge we want for treatment planning and the morbidity entailed to get it.
Eichner et al. were among the first gynecologists to evaluate in vivo lymphatic drainage of the vulva.4 Drawings from these procedures using sky blue vital dye demonstrated the methodical drainage of the vulva to the inguinal nodes. However, these studies were conducted with subcutaneously injected dye and errantly suggested that direct drainage also existed to the pelvic nodes. Further evaluation, by Parry-Jones clarified the rarity of this event, which mirrored our clinical experience and provided a segway for development of node finding techniques.5 The first discussion of a clinical utility to the sentinel node group for the vulva was made in 1979 by DiSaia and colleagues noting that no patients with femoral metastases had negative superficial inguinal nodes.6 Following the experience reported by Cabanas,7 DiSaia suggested that the superficial inguinal nodes were first to receive lymphatic flow and therein represented the nodes most at risk for metastatic involvement. Our current understanding of the true inguinal-femoral sentinel node(s) now follows from functional pathways and not anatomical localization. Experience from nodal mapping procedures in vulvar squamous cell carcinoma demonstrate these high-risk nodes rest most often within the 8 to 10 nodes which make up the superficial and medial deep inguinal basins.8
In the current issue of the Annals of Surgical Oncology, Abramova and colleagues9 report their experience with lymphatic mapping and sentinel node localization in six patients with urogenital melanoma. The well-written article highlights the important issues and difficulties in making a sound recommendation regarding urogenital, particularly vulvar, melanoma management and adds to the growing experience of mapping technology for vulvar malignancy. The authors’ findings echo those of others and provide a forum of discussion for inguinal-femoral sentinel biopsy as an evolutionary step in the evaluation of the groin.
This latter claim is not to be taken casually as failure to identify early nodal metastases could sanction a mortal outcome. Attempts at sentinel node biopsy in lieu of lymphadenectomy have been piloted. Rodier et al. identified one node-positive patient by sentinel biopsy from eight patients (6 squamous cell, 2 melanoma) using dye, lymphoscintigraphy, and a combination of both.10 They suggested the technique was a promising strategy, yet one patient suffered a groin recurrence at 6 months. Terada et al. reported on nine patients with T1 squamous cell lesions undergoing preoperative sentinel biopsy by the combined technique.11 One patient was found with metastatic involvement in an ipsilateral groin with a contralateral negative sentinel node. Following ipsilateral completion lymphadenectomy and radical vulvar excision she subsequently developed a fatal recurrence in the contralateral groin. Post hoc immunohistochemical staining of the negative sentinel node for cytokeratin revealed a micrometastatic focus. The authors suggested the technique was feasible and that immunohistochemical ultrastaging be performed to identify subclinical nodal metastases in negative hematoxylin and eosin sentinel nodes. In the current trial, the authors were able to identify a sentinel node in all cases using lymphoscintigraphy alone, but no node-positive cases were identified. This along with the relatively short follow-up interval limits the recommendation of sentinel node biopsy alone as a tool for node-based treatment triage protocols.
Another challenge to vulvar sentinel node mapping is the generalization of application to the gynecologic oncology community. Previous attempts at multi-institutional evaluation have been met with limited success. Ansink et al. studying early stage squamous cancers demonstrated that the dye-only technique identified sentinel nodes in just 56% of basins at risk and 2 of 11 node-positive patients had negative blue sentinel nodes (false negatives).12 It was of interest that three centers in this study had experience with six or fewer cases. On the other hand, multisurgeon series using lymphoscintigraphy or the combination of dye and lymphoscintigraphy have rarely reported a false-negative case. As observed in the current article, lymphoscintigraphy ahead of surgery (up to 18 hours) along with hard copy lymphoscintigrams aids in the process of node localization and significantly lowers the learning curve against dye alone techniques. Critical to this discussion as well is the role of second echelon nodes. Duration of the scintigraphic study and radionuclide particle size more prominently identify these nodes. Cases where several candidate sentinels were in need of sampling would defeat the purpose of sentinel node mapping, yet a clear distinction between primary and secondary pathways is required for precise mapping.
Finally, general application will require definition of an acceptable false-negative rate. Not surprising, compared with physicians surveyed, patients are much less willing to accept a low false-negative rate. de Hullu and colleagues found recently that 60% of surviving vulvar cancer patients were unwilling to accept a 5% false-negative sentinel node rate even though nearly half had continued severe pain and lymphedema from their complete inguinal-femoral dissections. On the other hand, 60% of their gynecologists would accept the procedure given a 5% to 20% false-negative rate.13 Validation must be based on node-positive cases; a difficult task for the uncommon vulvar cancer, much more so for the even rarer vulvar melanoma. Experience in other disease sites, such as melanoma and breast cancer have defined a learning curve, which stabilizes after 20 or 30 cases. Such a number applied to an individual gynecologic oncologist may take years or a career to amass. The Gynecologic Oncology Group is currently validating sentinel node localization in a multi-institutional setting through protocol number 173.
Ultimately, where does this technology take us? It is likely that protocols of therapy will be based on the outcome of the sentinel node. It is not inconceivable that sentinel node localization and pathological processing will be done as an outpatient, preoperative procedure, thus dictating the type of surgery to be rendered at primary tumor extirpation. However, methodology of intraoperative assessment (frozen section, immunohistochemistry, and so on), defining an acceptable rate of false-negative determinations, and the appropriate surgery to perform in node-positive cases (or those who will receive adjuvant therapy) are among the many subsequent hurdles physicians and patients will need to address before this supplants our time-tested standard. In the end, cooperative randomized trials will be necessary to make the convincing argument.
Received for publication September 10, 2002. Accepted for publication September 18, 2002.
REFERENCES
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