Quantitative Measurement of Melanoma Spread in Sentinel Lymph Nodes and Survival

Background Sentinel lymph node spread is a crucial factor in melanoma outcome. We aimed to define the impact of minimal cancer spread and of increasing numbers of disseminated cancer cells on melanoma-specific survival. Methods and Findings We analyzed 1,834 sentinel nodes from 1,027 patients with ultrasound node-negative melanoma who underwent sentinel node biopsy between February 8, 2000, and June 19, 2008, by histopathology including immunohistochemistry and quantitative immunocytology. For immunocytology we recorded the number of disseminated cancer cells (DCCs) per million lymph node cells (DCC density [DCCD]) after disaggregation and immunostaining for the melanocytic marker gp100. None of the control lymph nodes from non-melanoma patients (n=52) harbored gp100-positive cells. We analyzed gp100-positive cells from melanoma patients by comparative genomic hybridization and found, in 45 of 46 patients tested, gp100-positive cells displaying genomic alterations. At a median follow-up of 49 mo (range 3-123 mo), 138 patients (13.4%) had died from melanoma. Increased DCCD was associated with increased risk for death due to melanoma (univariable analysis; p<0.001; hazard ratio 1.81, 95% CI 1.61-2.01, for a 10-fold increase in DCCD + 1). Even patients with a positive DCCD 3 had an increased risk of dying from melanoma compared to patients with DCCD=0 (p=0.04; hazard ratio 1.63, 95% CI 1.02-2.58). Upon multivariable testing DCCD was a stronger predictor of death than histopathology. The final model included thickness, DCCD, and ulceration (all p<0.001) as the most relevant prognostic factors, was internally validated by bootstrapping, and provided superior survival prediction compared to the current American Joint Committee on Cancer staging categories. Conclusions Cancer cell dissemination to the sentinel node is a quantitative risk factor for melanoma death. A model based on the combined quantitative effects of DCCD, tumor thickness, and ulceration predicted outcome best, particularly at longer follow-up. If these results are validated in an independent study, establishing quantitative immunocytology in histopathological laboratories may be useful clinically.Please see later in the article for the Editors' Summary Editors' Summary Background Because the skin contains many different cell types, there are many types of skin cancer. The most dangerous typemelanomadevelops when mutations occur in melanocytes, the cells that produce the pigment melanin. Less than 5% of skin cancers are melanomas, but melanoma causes most skin cancer deaths. Early signs of melanoma are a change in the appearance of a mole (a pigmented skin blemish) or the development of a new and unusual pigmented lesion. If these signs are noticed and the melanoma is diagnosed before it has spread from the skin into nearby lymph nodes and other tissues, surgery often provides a cure. For advanced melanomas, the outlook is generally poor, although novel therapies may prolong a patient's life. Why Was This Study Done? When a person is diagnosed with melanoma, it is important to stage the tumor. Knowing the extent and severity of the melanoma helps oncologists plan treatments and estimate their patients' likely outcomes. The detection of isolated melanoma cells in sentinel lymph nodes (the nodes to which cancer cells are most likely to spread from a primary tumor) is included in melanoma staging recommendations. However, finding rare tumor cells in sentinel lymph node biopsies by examining the tissue requires the analysis of many slides from each node removed from the patient and is extremely time-consuming. In this study, the researchers investigate the predictive value of a quantitative immunocytological assay that involves disaggregation of the sentinel node and detection of disseminated cancer cells (DCCs) by immunostaining for gp100 (a marker for melanoma cells). They also use this new assay to examine the effect of increasing numbers of DCCs on melanoma-specific survival. What Did the Researchers Do and Find? The researchers used routine histopathology and immunocytology to analyze 1,834 sentinel lymph nodes from 1,027 patients with melanoma who underwent sentinel lymph node biopsy at one German hospital. For immunocytology, the researchers recorded the number of gp100-positive cells per million lymph node cells (the DCC density). During follow-up, 138 patients (13.4%) died from melanoma. The results indicated that increased DCC density was associated with an increased risk of death due to melanoma. Specifically, every 10-fold increase in DCC density + 1 was associated with a near doubling of the risk of death from melanoma (a hazard ratio of 1.81). Even patients with three or fewer gp100-positive cells per million lymph node cells had an increased risk of dying from melanoma compared to patients with no gp100-positive cells (hazard ratio 1.63). When other predictors of outcome such as age and primary tumor location were taken into account, DCC density was a stronger predictor of death than histopathology. Finally, a survival model that included tumor thickness, tumor ulceration, and DCC density provided survival prediction superior to that of a model based on the current standard staging recommendations. What Do These Findings Mean? These findings show that quantification of cancer cell dissemination from melanomas to sentinel lymph nodes is feasible and can be combined with other characteristics of the primary tumor to provide an accurate prediction of outcomes for individual patients with melanoma. Notably, the new prediction model identifies a group of patients at high risk of progression for whom the current clinical standard underestimates the risk of death. These patients may benefit from adjuvant therapies, so the new analysis presented in this study may help to stratify patients for clinical trials. Importantly, quantitative immunocytology and the new model, although internally validated in this study, need to be validated in an independent group of patients before they can be considered for routine clinical use. If external validation is successful, quantitative immunocytology, which is much less labor-intensive than histopathology, has the potential to change the routine clinical care of patients with melanoma and probably with other solid tumors, conclude the researchers. Additional Information Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001604. The US National Cancer Institute provides information for patients and professionals on melanoma, cancer staging, and sentinel lymph node biopsy (in English and Spanish) The nonprofit organization American Cancer Society provides information in several languages on cancer and how it develops and specific information on melanoma, including the AJCC system for staging and personal stories The UK National Health Service Choices website includes an introduction to cancer and a page on melanoma that includes personal stories The nonprofit organization Cancer Research UK provides basic information about cancer and detailed information on melanoma