Melanoma: MSLT-1—putting sentinel lymph node biopsy into context
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246 | MAY 2014 | VOLUME 11 www.nature.com/nrclinonc
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melanoma-specific survival if they had SLNB and EPLND. The hazard ratio was 0.67 (P = 0.04), when only melanomas of intermediate thickness are consideredthere was no difference between arms for thicker melanomas. The analysis of a small subset, the possibility of subtle ascertain-ment bias, and the borderline statistical signifi cance of this finding casts doubt on this conclusion.
From this study one cannot conclude that no patient with primary melanoma would benefit from a SLN-directed EPLND. One can only say that no benefit could be detected in a well-designed and meticu-lously executed randomized study of 1,661 patients. To determine more precisely if EPLND can affect survival, MSLT-2 will assess patients who are already defined to have nodal involvement by a positive SLN and they will be randomly assigned to EPLND or ultrasound monitoring and observation. Yet, without the results of that study, one must ask, how has SLNB become the standard of care for inter mediatethick-ness melanomas? Guidelines for the staging and therapy of melanoma that include SLNB have been widely accepted in the USA, Canada, Europe, Australia, and New Zealand.6 These guidelines go beyond the current British recommendation that this surgery is a staging procedure that has no proven therapeutic value.7 Nodal staging has been advocated by some because of the availability of adjuvant interferon- (IFN) for patients with nodal involvement, yet IFN has not been shown to clearly improve survival of patients with melanoma either.8 So, an expensive procedure that costs approximately US$10,000$15,0009 and without a proven survival benefit is being used to justify the use of a toxic adjuvant that also has no clear survival benefit. Such recommendations cannot represent the best data-driven use of our healthcare dollars. The best current evidence of whether to perform SLNB when a patient and their doctor are faced with a new diagnosis of primary melanoma is provided by the definitive result of MSLT1: No significant treatment-related difference in the 10-year melanoma-specific survival rate was seen in the overall study population.5 Certainly, there is prognostic information in a SLNB, and its use in defining patients for research studies is justifiable. Yet, without additional data showing that it can improve survival, it must be considered an expensive and optional staging tool and understood as such by patients considering this procedure.
Surgery Branch, Center for Cancer Research, National Cancer Institute, CRC Room 3-5952, 9000 Rockville Pike, Bethesda, MD 20892, USA (J.C.Y., R.M.S., S.A.R.). Correspondence to: S.A.R. firstname.lastname@example.org
Competing interestsThe authors declare no competing interests.
1. Morton, D.L. et al. Technical details of intraoperative lymphatic mapping for early stage melanoma. Arch. Surg. 127, 392399 (1992).
2. Veronesi, U. et al. Inefficacy of immediate node dissection in stage 1 melanoma of the limbs. N. Engl. J. Med. 297, 627630 (1977).
3. Balch, C.M. et al. Long-term results of a multi-institutional randomized trial comparing prognostic factors and surgical results for intermediate thickness melanomas (1.0 to 4.0 mm). Ann. Surg. Oncol. 7, 8797 (2000).
4. Morton, D.L. et al. Sentinel-node biopsy or nodal observation in melanoma. N. Engl. J. Med. 355, 13071317 (2006).
5. Morton, D.L. et al. Final trial report of sentinel-node biopsy versus nodal observation in melanoma. N. Engl. J. Med. 370, 599609 (2014).
6. Fong, Z.V. & Tanabe, K.K. Comparison of melanoma guidelines in the U.S.A., Canada, Europe, Australia and New Zealand: a critical appraisal and comprehensive review. Br. J. Dermatol. 170, 2030 (2014).
7. Marsden, J.R. et al. Revised UK guidelines forthe management of cutaneous melanoma 2010. Br. J. Dermatol. 163, 238256 (2010).
8. Kirkwood, J.M. et al. A pooled analysis of eastern cooperative oncology group and intergroup trials of adjuvant high-dose interferon for melanoma. Clin. Cancer Res. 10, 16701677 (2004).
9. Agness, D.M. Cost-effectiveness of sentinel lymph node biopsy in thin melanomas. Surgery 134, 542547 (2003).
MSLT1putting sentinel lymph node biopsy into contextVernon K.Sondak and Jonathan S.Zager
The MSLT-1 study compared sentinel lymph node biopsy (SLNB) with nodal observation in patients with localized cutaneous melanoma. The final results of the trialconducted from 1994 to 2002strongly support using SLNB in staging patients with melanomas 1.0 mm in thickness, but the optimal staging approach for thinner melanomas is unanswered. Sondak, V.K. & Zager, J.S. Nat. Rev. Clin. Oncol. 11, 246248 (2014); published online 15 April 2014; doi:10.1038/nrclinonc.2014.66
Sentinel lymph node biopsy (SLNB) for the surgical staging of clinically node-negative cutaneous melanoma, which was intro-duced by Morton etal. in 1992,1 has been broadly accepted worldwide, albeit with some islands of controversy.2 Two large pro-spective evaluations of SLNB were carried out in the years following its i ntroduction the Sunbelt Melanoma Trial,3 which involved over 3,600 patients with melano-mas 1.0 mm undergoing SLNB, and the Multicenter Selective Lymphadenectomy Trial-1 (MSLT-1).4,5 MSLT-1 is the only randomized trial of SLNB ever conducted; it randomly assigned 2,001 patients in a 60:40 ratio to either SLNB or nodal obser-vation. Patients with positive nodes (found at SLNB or upon recurrence) underwent radical lymphadenectomy. The primary end point was melanoma-specific survival, with secondary end points including relapse-free survival (RFS) and melanoma-specific survival for the subset of node-positive patients. Outcomes in patients with posi-tive sentinel nodes, who underwent early
lymphadenectomy, were compared with outcomes in those who underwent delayed lymphadenectomy at the time of nodal relapse. Results of 1,661 patients with mela-nomas 1.2 mm in t hickness were included in the final report.
Supporting a wealth of other data, the MSLT-1 trial confirmed that sentinel node status is the most important prognostic factor for clinically localized melanomas 1 mm in thickness. A positive sentinel node was detected in about 20% of patients, and approximately 5% of patients with a nega-tive SLNB developed nodal recurrence. RFS was signifi cantly improved in the SLNB arm, largely due to a much lower rate of regional nodal recurrence than noted in the obser-vation arm. However, melanoma-specific survival was not significantly different for
this finding is more than sufficient to justify routine use ofthe procedure
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SLNB and observation (81.4% versus 78.3% respectively, P = 0.18). Among patients with a positive node, distant metastasis- free and melanoma- specific survi val rates were improved for patients with intermediate- thickness melanoma (defined as 1.23.5 mm in the studys pri mary stratum or as 1.0 4.0 mm in keep ing with standard staging cri-teria, which is provided in the studys sup-plementary material) who were randomly assigned to undergo SLNB, but there were no signifi cant differences between the two arms in those patients with thick (in this case >3.5 mm) node- positive melanoma. RFS for patients with thick melanomas was significantly improved in the SLNB arm, largely due to many fewer nodal recurrences in that arm. The finding that both distant metastasis- free survival and melanoma- specific survival were significantly impro-ved for patients with intermediate-thickness melanoma randomly assigned to undergo SLNB suggests that early diagnosis and surgical treatment of node-positive mela-noma can improve o utcomes dramatically.5 Morbid ity of l ymphadenectomye specially l ymphoedemawas less among patients undergoing early lymphadenectomy after a positive SLNB compared with those under-going later l ymphadenectomy at the time ofrecurrence.6
Of note, the primary analysis group for MSLT-1 was the stratum of patients with melanomas between 1.2 and 3.5 mm thick-ness, as these patients were considered to have the greatest chance for demon strating an improved outcome for early inter vention in node-positive cases. This indeed proved to be the case: although the prognostic signifi cance and improvement in RFS were maintained in patients with thicker mela-nomas, there were no significant differ-ences in distant metastasis-free survival and melanoma- specific survival for node-positiv e patients with melanomas >3.5 mm thick. While this observation supports the long-held view that patients with node- positive thick melanomas have such a high risk for occult distant metastasis that early surgical intervention offers limited poten-tial to impact survival,7 the very high risk
of posi tive nodes and the short disease-free inter val before nodes became palpable on the observation arm (median time 9.2months for melanomas >3.5 mm),5 combined with the significantly improved RFS after SLNB in these patients, argues strongly for routine use of SLNB in clinically node-negative patients with thickmelanomas.
However, does early lymphadenec-tomy for sentinel node-positive patients really improve survival for patients with intermediate- thickness melanoma or is this finding an artefact of the study design? Attribution bias is a factor to consider in thisregard, as all patients with a positive senti nelnode are identified early in the intervention arm, whereas node-positive patients on the observation arm are only identified after a period of follow-up. Some patients with very late nodal relapse in the observation gro