Resistance to dermcidin-derived peptides is independent of bacterial protease activity.

Dermcidin (DCD) is an antimicrobial peptide constitutively expressed in eccrine sweat glands in human skin. By post-secretory proteolytic processing in sweat, the DCD protein gives rise to anionic and cationic DCD peptides that are able to kill several Gram-positive and Gram-negative bacteria but are only weakly active against Pseudomonas aeruginosa. Here, we questioned whether bacterial resistance to DCD peptides is mediated by proteolytic degradation. It was shown that DCD-derived peptides are degraded by purified bacterial proteases and by extracellular proteases secreted by P. aeruginosa in a concentration-dependent manner. However, protease-deficient mutants of P. aeruginosa PAO1 lacking either lasA, lasB (elastase) or both showed a similar sensitivity towards DCD-derived peptides as the wild-type strain. Finally, inhibition of total protease activity indicated that proteases secreted by P. aeruginosa are not responsible for the poor activity of DCD-derived peptides against P. aeruginosa. These data suggest that the decreased sensitivity of P. aeruginosa to DCD-derived peptides is not mediated by proteolytic degradation under physiological conditions.

Lysis of a broad range of epithelial tumour cells by human gamma delta T cells: involvement of NKG2D ligands and T-cell receptor- versus NKG2D-dependent recognition.

Human gammadelta T cells expressing a V gamma 9V delta 2 T-cell receptor (TCR) kill various tumour cells including autologous tumours. In addition to TCR-dependent recognition, activation of NKG2D-positive gammadelta T cells by tumour cell-expressed NKG2D ligands can also trigger cytotoxic effector function. In this study, we investigated the involvement of TCR versus NKG2D in tumour cell recognition as a prerequisite to identify tumour types suitable for gammadelta T-cell-based immunotherapy. We have characterized epithelial tumour cells of different origin with respect to cell surface expression of the known NKG2D ligands MHC class I-chain-related antigens (MIC) A/B and UL16-binding proteins (ULBP), and susceptibility to gammadelta T-cell killing. Most tumour cells expressed comparable levels of MICA and MICB as well as ULBP with the exception of ULBP-1 which was absent or only weakly expressed. Most epithelial tumours were susceptible to allogeneic gammadelta T-cell lysis and in the case of an established ovarian carcinoma to autologous gammadelta T-cell killing. Lysis of resistant cells was enhanced by pre-treatment of tumour cells with aminobisphosphonates or pre-activation of gammadelta T cells with phosphoantigens. A potential involvement of TCR and/or NKG2D was investigated by antibody blockade. These experiments revealed three patterns of inhibition, i.e. preferential inhibition by anti-TCR antibody, preferential inhibition by anti-NKG2D antibody, or additive blockade by anti-TCR plus anti-NKG2D antibodies. Our results indicate for the first time that the NKG2D pathway is involved in the lysis of different melanomas, pancreatic adenocarcinomas, squamous cell carcinomas of the head and neck, and lung carcinoma.

Combined targeting of MAPK and AKT signalling pathways is a promising strategy for melanoma treatment.

BACKGROUND: In melanoma, several signalling pathways are constitutively activated. Among them, the RAS/RAF/MEK/ERK (MAPK) and PI3K/AKT (AKT) signalling pathways are activated through multiple mechanisms and appear to play a major role in melanoma development and progression. OBJECTIVES: In this study, we examined whether targeting the MAPK and/or AKT signalling pathways would have therapeutic effects against melanoma. METHODS: Using a panel of pharmacological inhibitors (BAY 43-9006, PD98059, U0126, wortmannin, LY294002) we inhibited the MAPK and AKT signalling pathways at different levels and evaluated the effects on growth, survival and invasion of melanoma cells in monolayer and organotypic skin culture. RESULTS: Antiproliferative and proapoptotic effects of inhibitors alone in monolayer culture were disappointing and varied among the different cell lines. In contrast, combined targeting of the MAPK and AKT signalling pathways significantly inhibited growth and enhanced apoptosis in monolayer culture. To verify our data in a more physiological context we incorporated melanoma cells into regenerated human skin mimicking the microenvironment of human melanoma. Combinations of MAPK and AKT inhibitors completely suppressed invasive tumour growth of melanoma cells in regenerated human skin. CONCLUSIONS: Combined targeting of MAPK and AKT signalling pathways is a promising strategy for melanoma treatment and should encourage further in-depth investigations.

Naturally processed dermcidin-derived peptides do not permeabilize bacterial membranes and kill microorganisms irrespective of their charge.

Dermcidin (DCD) is a recently described antimicrobial peptide, which is constitutively expressed in eccrine sweat glands and transported via sweat to the epidermal surface. By postsecretory proteolytic processing in sweat the dermcidin protein gives rise to several truncated DCD peptides which differ in length and net charge. In order to understand the mechanism of antimicrobial activity, we analyzed the spectrum of activity of several naturally processed dermcidin-derived peptides, the secondary structure in different solvents, and the ability of these peptides to interact with or permeabilize the bacterial membrane. Interestingly, although all naturally processed DCD peptides can adopt an alpha-helical conformation in solvents, they have a diverse and partially overlapping spectrum of activity against gram-positive and gram-negative bacteria. This indicates that the net charge and the secondary structure of the peptides are not important for the toxic activity. Furthermore, using carboxyfluorescein-loaded liposomes, membrane permeability studies and electron microscopy we investigated whether DCD peptides are able to permeabilize bacterial membranes. The data convincingly show that irrespective of charge the different DCD peptides are not able to permeabilize bacterial membranes. However, bacterial mutants lacking specific cell envelope modifications exhibited different susceptibilities to killing by DCD peptides than wild-type bacterial strains. Finally, immunoelectron microscopy studies indicated that DCD peptides are able to bind to the bacterial surface; however, signs of membrane perturbation were not observed. These studies indicate that DCD peptides do not exert their activity by permeabilizing bacterial membranes.

Dermcidin is constitutively produced by eccrine sweat glands and is not induced in epidermal cells under inflammatory skin conditions.

BACKGROUND: Antimicrobial peptides (AMPs) are important effector molecules of innate immunity, protecting epithelial surfaces of multicellular organisms. In human skin two classes of AMPs-the beta-defensins and the cathelicidins-are produced by keratinocytes primarily under inflammatory conditions. In contrast, dermcidin (DCD), a recently discovered AMP with broad-spectrum activity, is expressed in eccrine sweat glands and transported via sweat to the epidermal surface. OBJECTIVES: To investigate whether DCD expression is induced under inflammatory conditions in epidermal keratinocytes. METHODS: Lesional skin of the inflammatory skin diseases atopic dermatitis, psoriasis and lichen planus was analysed by immunohistochemistry using a polyclonal anti-DCD antiserum. We also examined whether DCD RNA expression is induced in cultured human keratinocytes, fibroblasts, melanocytes and melanoma cells. RESULTS: Whereas DCD was constitutively expressed in eccrine sweat glands of all skin biopsies, we found that, independent of the type of the inflammatory skin lesion, DCD protein expression was not induced in human epidermal keratinocytes. In contrast, beta-defensin 2 was expressed in epidermal keratinocytes of inflammatory human skin, but not in keratinocytes of healthy human skin. Upon stimulation of the cultured cells with 12-O-tetradecanoyl-phorbol-13-acetate, tumour necrosis factor-alpha, lipopolysaccharide or H2O2, DCD mRNA expression was not detected in primary keratinocytes, fibroblasts and melanocytes, but was detected in MeWo and SKMEL28 melanoma cells. CONCLUSIONS: These results indicate that, unlike human cathelicidins and beta-defensins which are inducible peptides that primarily function in response to injury and inflammation, DCD is exclusively part of the constitutive innate defence of human skin. By modulating surface colonization, DCD may help to prevent local and systemic invasion of pathogens.

Additional reverse transcription-polymerase chain reaction of peripheral slices is not superior to analysis of the central slice in sentinel lymph nodes from melanoma patients.

BACKGROUND: The status of the sentinel lymph node (SLN) is an important prognostic factor in patients with cutaneous melanoma. Reverse transcription-polymerase chain reaction (RT-PCR) has been used as a sensitive means of detecting tumour cells in SLNs. OBJECTIVES: To determine whether RT-PCR analysis of the SLN using both the central and the peripheral slices is more sensitive than molecular analysis of the central slice only. METHODS: Eighty-three SLNs from 59 patients with primary cutaneous melanoma were identified by SLN mapping. All SLNs were bisected along their longitudinal axis to produce two equal halves. One half was used for histology and immunohistochemistry, and the other was analysed by RT-PCR for tyrosinase and MelanA. Parallel to the longitudinal axis, one central slice (approximately 2 mm in thickness) was cut manually. This central slice was used for our standard RT-PCR protocol. In the current study, up to eight additional peripheral slices (each approximately 2 mm in thickness) were cut parallel to the existing cut surface. These peripheral slices were analysed by additional RT-PCR. RESULTS: Standard RT-PCR of the central slice yielded positive results in 34 of 59 patients (57%). Additional RT-PCR of peripheral slices demonstrated positive findings in six additional patients (10%) who were initially negative by standard RT-PCR of the central slice. In detail, seven of those 34 patients positive by standard RT-PCR of the central slice had positive histological findings. In each of these seven patients, RT-PCR was positive both in the central slice as well as in the peripheral slices. The remaining 27 patients with positive RT-PCR results of the central slice showed negative histological findings. Only nine (33%) of these 27 patients had a positive RT-PCR also in the peripheral slices. Finally, all 25 patients with negative RT-PCR results in the central slice showed negative histological findings. Six of these patients (24%) revealed positive RT-PCR results on the analysis of peripheral slices. However, three of these patients expressed only MelanA but not tyrosinase. Thirty lymph nodes from 24 nonmelanoma patients served as negative controls for RT-PCR. In three of these 24 patients (13%) expression of MelanA but not tyrosinase was detected by RT-PCR. CONCLUSIONS: Molecular analysis of peripheral slices yielded six additional patients (10%) positive by RT-PCR who were initially negative by standard RT-PCR of the central slice. However, three of these six patients were found to express only MelanA but not tyrosinase. As MelanA expression was also found in 13% of control lymph nodes, positive MelanA expression alone in SLNs of melanoma patients requires cautious interpretation in order to avoid false-positive findings. Thus, additional molecular processing of peripheral slices did not significantly increase the number of patients with RT-PCR-positive SLNs.

Metastatic pathways and time courses in the orderly progression of cutaneous melanoma.

BACKGROUND: It is known that two-thirds of patients who develop clinical metastases following treatment of a primary cutaneous melanoma initially present with locoregional metastases and one-third initially present with distant metastases. However, few reports in the literature give detailed figures on different metastatic pathways in cutaneous melanoma. OBJECTIVES: The aim of the present study was to perform a detailed analysis of the different metastatic pathways, the time course of the development of metastases and the factors influencing them. METHODS: In a series of 3001 patients with primary cutaneous melanoma at first presentation, 466 subsequently developed metastasis and were followed-up over the long term at the University of Tuebingen, Germany between 1976 and 1996. Different pathways of metastatic spread were traced. Associated risk factors for the different pathways were assessed. Differences in survival probabilities were calculated by the Kaplan-Meier method and evaluated by the log-rank test. RESULTS: In 50.2% of the patients the first metastasis after treatment of the primary tumour developed in the regional lymph nodes. In the remaining half of the patient sample the first metastasis developed in the lymphatic drainage area in front of the regional lymph nodes, as satellite or in-transit metastases (21.7%) or as direct distant metastases (28.1%). Anatomical location, sex and tumour thickness were significant risk factors for the development of metastasis by different pathways. The most important risk factor appeared to be the location of the primary tumour. The median intervals elapsing before the first metastasis differed significantly between the different metastatic pathways. The direct distant metastases became manifest after a median period of 25 months, thus later than the direct regional lymph node metastases (median latency period, 16 months) and the direct satellite and in-transit metastases (median latency period, 17 months). In patients who developed distant metastases the period of development was independent of the metastatic route. The time at which the distant metastases developed was roughly the same (between 24 and 30 months after the detection of the primary tumour), irrespective of whether satellite or in-transit metastases, lymph node metastases or distant metastases were the first to occur. CONCLUSIONS: The time course of the development of distant metastasis was more or less the same irrespective of the metastatic pathway; this suggests that in patients with in-transit or satellite metastasis or regional lymph node metastasis, haematogenic metastatic spread had already taken place. Thus, the diagnostic value of sentinel lymph node biopsy and the therapeutic benefit of elective lymph node dissection may be limited, as satellite and in-transit metastases or direct distant metastases will not be detected and haematogenous spread may already have taken place when the intervention is performed.

Dermcidin: a novel human antibiotic peptide secreted by sweat glands.

Antimicrobial peptides are an important component of the innate response in many species. Here we describe the isolation of the gene Dermcidin, which encodes an antimicrobial peptide that has a broad spectrum of activity and no homology to other known antimicrobial peptides. This protein was specifically and constitutively expressed in the sweat glands, secreted into the sweat and transported to the epidermal surface. In sweat, a proteolytically processed 47-amino acid peptide was generated that showed antimicrobial activity in response to a variety of pathogenic microorganisms. The activity of the peptide was maintained over a broad pH range and in high salt concentrations that resembled the conditions in human sweat. This indicated that sweat plays a role in the regulation of human skin flora through the presence of an antimicrobial peptide. This peptide may help limit infection by potential pathogens in the first few hours following bacterial colonization.

Detection of melanoma cells in sentinel lymph nodes, bone marrow and peripheral blood by a reverse transcription-polymerase chain reaction assay in patients with primary cutaneous melanoma: association with Breslow's tumour thickness.

BACKGROUND: Tyrosinase reverse transcription-polymerase chain reaction (RT-PCR) has been shown to be highly sensitive in detecting tumour cells in melanoma patients. OBJECTIVE: To assess whether the detection of minimal residual disease by RT-PCR is improved by concomitant analysis of sentinel lymph nodes (SLNs), bone marrow (BM) and peripheral blood (PB) in patients with primary melanoma. METHODS: Thirty-five SLNs, 41 BM samples and 26 PB specimens from 26 patients with primary cutaneous melanoma (tumour thickness > or = 0.75 mm) were examined by nested RT-PCR for tyrosinase and Melan-A. SLNs and BM samples were also analysed by histopathology. RT-PCR findings were related to tumour thickness of the primary melanoma. RESULTS: Overall, melanoma cells were detected by RT-PCR in 13 of 26 patients (50%). Seven patients had positive RT-PCR results in their SLNs (27%), including all patients (n = 4) with histologically positive SLNs, two patients had positive findings in their BM exclusively detected by RT-PCR (8%) and six patients in PB (23%). The presence of tumour cells detected by RT-PCR in SLNs was not related to the presence of melanoma cells in BM and/or PB. The incidence of RT-PCR-positive SLNs was significantly associated with greater tumour thickness (P = 0.004). Both patients with positive RT-PCR findings in their BM had a large tumour thickness (> or = 2 mm). No association between positive RT-PCR findings in PB and greater tumour thickness was observed. CONCLUSIONS: RT-PCR-positive SLNs were strongly associated with greater tumour thickness, underlining the prognostic significance of SLN positivity. Similar to certain epithelial malignancies, molecular investigation of the BM might provide complementary prognostic information in the early stages of melanoma. In contrast, no association between positive RT-PCR results in PB and increasing tumour thickness was found, implying that RT-PCR findings in PB are of doubtful clinical relevance in primary melanoma.

HLA-A2 restricted, melanocyte-specific CD8(+) T lymphocytes detected in vitiligo patients are related to disease activity and are predominantly directed against MelanA/MART1.

Vitiligo is a skin and hair disorder characterized by circumscribed depigmented lesions due to lack of melanocytes in the respective areas. It has been suggested that vitiligo is caused by an autoimmune-mediated destruction of melanocytes. Recently, the presence of a high frequency of skin-homing melanocyte-specific cytotoxic T lymphocytes in the peripheral blood of patients with vitiligo was reported. Our study examines the frequency of melanocyte-specific cytotoxic T lymphocytes in vitiligo patients and its relationship to disease activity. Thirty-two patients with moderate to active vitiligo and 17 control subjects were included. Melanocyte specific reactive CD8(+) T cells were identified by enzyme-linked immunospot assay after stimulation with five peptides from gp100, four peptides from MelanA/MART1, and two peptides from tyrosinase. In selected patients, intracellular interferon-gamma staining for the detection of specific reactive CD8(+) T cells was additionally performed. In seven of 10 patients (70%) with actively progressive disease CD8(+) T cells directed against melanocyte epitopes were detected, whereas only in four of 22 patients (18%) with moderate disease activity such specific reactivity was found. MelanA/MART1 peptides were immunodominant in nine patients reacting against EAAGIGILTV and three patients reacting against ILTVILGVL. Intracellular interferon-gamma staining confirmed the findings obtained by the enzyme-linked immunospot technique. The present study supports the hypothesis that vitiligo is a cytotoxic T lymphocyte-mediated autoimmune disease. The presence of melanocyte-specific reactive CD8(+) T cells seems to be closely related to disease activity.

Interlaboratory evaluation of a new reverse transcriptase polymerase chain reaction-based enzyme-linked immunosorbent assay for the detection of circulating melanoma cells: a multicenter study of the Dermatologic Cooperative Oncology Group.

PURPOSE: Reverse transcription-polymerase chain reaction (RT-PCR)-based detection of tyrosinase mRNA is the most frequently used laboratory method for the detection of circulating tumor cells in melanoma patients. However, previously published results showed considerable variability in the PCR positivity rates. MATERIALS AND METHODS: We designed a collaborative study to assess the sensitivity, specificity, and clinical relevance of a new standardized RT-PCR-based enzyme-linked immunosorbent assay (ELISA) for the detection of circulating melanoma cells. Blood samples of healthy donors mixed with cells of a melanoma cell line were prepared in a blinded fashion, and aliquots were sent to seven participating laboratories experienced in RT-PCR. RESULTS: The results demonstrate a high sensitivity (1 melanoma cell/mL blood) and specificity (no false-negatives and 7.4% [2 of 28] false-positives) of the assay and a satisfactory rate of interlaboratory reproducibility. The analysis of aliquots of blinded samples derived from 60 melanoma patients identified tyrosinase mRNA in 17 of 60 (28.3%): three (20%) of 15 stage I patients, two (13.3%) of 15 stage II patients, five (35.7%) of 14 stage III patients, and seven (43.8%) of 16 stage IV patients. The interlaboratory reproducibility of positive samples, however, was extremely low and indicates the presence of low amounts of target mRNA. CONCLUSION: Reverse transcriptase-PCR ELISA has a high sensitivity and specificity for the detection of tyrosinase mRNA in peripheral blood cells. The low interlaboratory reproducibility for the detection of tumor cells in blood samples of melanoma patients, however, raises the question of relevance of this assay for clinical use.

Polymerase chain reaction in the detection of circulating tumour cells in peripheral blood of melanoma patients.

Conflicting results were obtained by various research groups using the tyrosinase reverse transcription polymerase chain reaction (RT-PCR) for detecting melanoma cells circulating in peripheral blood. Whereas 100% positivity was initially reported for stage IV patients, more recent investigations reported positive detection rates between 30% and 50% in patients with disseminated melanoma. While the high detection rate initially reported in metastatic melanoma may be explained by contamination problems, methodological differences in different steps of the technical procedure of RT-PCR may account for the differences reported in more recent examinations. Major differences may result from the kind of blood preparation, the RNA isolation method, the kind of RT enzyme used, and the gene targeted by PCR primers. In our experience, blood purification by a Ficoll gradient increased melanoma cell detection rates compared to RNA extraction from total blood or after erythrocyte lysis. Amplification of MelanA in addition to tyrosinase resulted in a 30% enhanced sensitivity of melanoma cell detection compared to amplification to tyrosinase alone, whereas gp100/pMel17 and MUC18 gene products were already detected in blood from nonmelanoma patients. These findings are in agreement with those of other groups. Currently, an increase in the sensitivity for detection of circulating tumour cells to more than 50% of patients with disseminated melanoma seems to be unlikely. It is interesting that between 15% and 30% positive results and sometimes more have already been obtained from patients with primary melanoma. So far, there is no data for judging the prognostic significance of the detection of circulating tumour cells in patients without clinically recognisable metastases. Our limited experience shows that staging examinations in these patients reveal no proof of macrometastasis. Therefore, it is presently unclear whether these positive findings are associated with long-term prognosis or if they merely reflect false positive findings in this highly sensitive RT-PCR technique.

Detection of micrometastasis in sentinel lymph nodes of patients with primary cutaneous melanoma.

The technique of sentinel lymph node (SLN) biopsy has been demonstrated to be highly predictive for the detection of melanoma micrometastases in the regional lymph node basin. Therefore, the SLN was proposed to accurately reflect the lymph node status of patients with primary cutaneous melanoma. As the regional lymph node status is one of the most powerful predictors of survival in patients with primary melanoma, the histopathologic assessment is critically important for accurate staging. In approximately 20% (ranging from 9% to 42%) of patients with primary melanoma, the SLN was found to be tumor-positive by histopathology or immunohistochemistry. However, the true incidence of metastatic melanoma cells in (sentinel) lymph nodes is underestimated by histopathologic examination. Recently, the method of reverse transcription-polymerase chain reaction (RT-PCR) for tyrosinase mRNA has been used as a molecular marker for the presence of melanoma cells. Tyrosinase RT-PCR was demonstrated to significantly increase the detection of melanoma cells in SLNs as compared to histopathology. All lymph nodes positive by histopathology were shown to express tyrosinase by RT-PCR. Furthermore, tyrosinase transcripts were also detected in 36-52% of stage I and II melanoma patients with SLNs negative by histopathology. Importantly, the recurrence rate was significantly higher in patients with histologically negative SLNs who were found to be positive by RT-PCR than in patients with negative results by both techniques. These findings indicate that RT-PCR status of the SLN is more sensitive for detection of minimal melanoma disease than histopathology. Therefore, the RT-PCR status of the SLN may be suitable to improve melanoma staging and may serve as a prognostic factor in patients with primary cutaneous melanoma.

Significance of serum protein S100 levels in screening for melanoma metastasis: does protein S100 enable early detection of melanoma recurrence?

A number of recent reports suggest serum protein S100 as a prognostic parameter in patients with metastatic melanoma. In the present study, serum protein S100 was investigated as a tumour marker for screening for melanoma metastasis in patients attending regular follow-up examinations. During the period from September 1997 to December 1998, serum protein S100 levels were measured by an immunoluminometric assay in 411 consecutive high risk melanoma patients (666 samples) and in 120 control subjects. Melanoma patients with resected primary tumours with a tumour thickness of 1.5 mm or more with resected metastasis were included in the study. Overall, 41 of the 411 patients developed metastasis during the period of observation. According to the distribution of protein S100 levels, the following different cut-off values were examined: 0.08 microg/l (95 percentile of the control group) and 0.13 microg/l (95 percentile of the group of melanoma patients without metastasis). The test efficiency for protein S100 as a diagnostic test for the detection of metastasis was highest for the cut-off value of 0.13 microg/l. In eight of the 41 patients (19.5%), elevation of protein S100 was the first sign of recurrence. Of the 41 patients with metastatic disease, 13 had elevated protein S100, giving a sensitivity of 0.32. The specificity for the detection of metastasis was 0.96. In eight of the 14 patients (57%) who developed distant metastasis, elevated S100 values were the first sign of tumour progression. In conclusion, determination of serum protein S100 levels enables earlier detection of distant metastasis in patients at high risk for metastasis. The impact on survival time needs to be investigated in follow-up studies.

Specifically regulated genes in malignant melanoma tissues identified by subtractive hybridization.

A polymerase chain reaction (PCR)-based subtractive hybridization technique was used to identify transformation-related genes in malignant melanoma. Melanoma biopsies were compared with tissues of benign melanocytic naevi and 549 gene fragments were screened using arrayed filters. Thirty-eight clones were confirmed to be differentially expressed representing 30 different genes (18 melanoma-specific and 12 naevus-specific genes). To further confirm differential gene expression, Northern blot analyses with six of the 30 genes as probes were performed. All six were differentially expressed in benign and malignant melanocytic lesions, specifically dbpB/YB-1, 67-kDa laminin receptor, CAGH-3, 71-kDa heat shock protein and two unknown genes. The expression levels of these genes were then analysed in 50 different tissues to determine their overall expression profile. In conclusion, the technique of PCR-based subtractive hybridization in combination with arrayed filters allows detection of differences in gene expression even in tissues from which high-quality RNA is hard to isolate. The genes identified in this study are of interest because of their potential role in the pathogenesis of malignant melanoma.

Examination of regional lymph nodes by sentinel node biopsy and molecular analysis provides new staging facilities in primary cutaneous melanoma.

Histopathologic parameters of the primary tumor, such as Breslow's tumor thickness and Clark's level of invasion are the current basis for prognostic classifications of primary cutaneous melanoma. Once patients develop regional node metastasis, histopathologic features of the primary melanoma no longer contribute significantly to survival prediction. In this tumor stage, the extent of lymph node involvement is the main prognostic factor. This study addresses the question whether application of a highly sensitive molecular biology assay for detection of submicroscopic melanoma cells in sentinel lymph nodes may be suitable to improve melanoma staging. One hundred and sixteen patients with primary cutaneous melanoma with a total of 214 sentinel lymph nodes were enrolled. Sentinel lymph nodes were analyzed by histopathology including immunohistochemistry and by reverse transcription-polymerase chain reaction for tyrosinase. Patients were examined for tumor recurrences during a follow-up period of 19 mo (median). Disease-free survival probabilities were calculated and independent prognostic factors were determined by multivariate analysis. Using histopathology, micrometastatic nodal involvement was detected in 15 patients (13%). Of the 101 patients with histopathologically negative sentinel lymph nodes, 36 were reclassified by positive tyrosinase reverse transcription-polymerase chain reaction and 65 patients were still negative by reverse transcription-polymerase chain reaction. Recurrences were observed in 23 (20%) of 116 patients. These tumor recurrences were demonstrated in 10 patients (67%) with histopathologically positive sentinel lymph nodes, in nine patients (25%) with submicroscopic tumor cells detected by reverse transcription-polymerase chain reaction, and in four patients (6%) negative by both methods. The differences in recurrence rates were statistically significant (p = 0.01). In a multivariate analysis, histopathologic and reverse transcription-polymerase chain reaction status of the sentinel lymph node were demonstrated to be the only significant prognostic factors for predicting disease-free survival. Tyrosinase reverse transcription-polymerase chain reaction for the detection of minimal residual melanoma in sentinel lymph nodes is a powerful tool to determine patients who are at increased risk for subsequent metastasis. Moreover, a group of patients with high tumor thickness was identified by negative reverse transcription-polymerase chain reaction to be at low risk for recurrent disease. These data may have an impact on future tumor classifications of primary cutaneous melanoma.

Increased sensitivity for the detection of malignant melanoma cells in peripheral blood using an improved protocol for reverse transcription-polymerase chain reaction.

Conflicting results have been obtained by various research groups using tyrosinase reverse transcription-polymerase chain reaction (RT-PCR) for detecting micrometastases in the blood of melanoma patients, with positive results ranging from 0 to 100% in disseminated melanoma. Methodological differences in the processing of blood samples may in part account for these discrepancies. The aim of this study was to standardize and optimize the experimental conditions for RT-PCR detection of melanoma cells in peripheral blood. We analysed the effect of different parameters of sample processing on the sensitivity of the tyrosinase RT-PCR using peripheral blood spiked with defined numbers of SKMEL28 melanoma cells. Purification of the mononuclear cell fraction using a Ficoll gradient with a density of 1.077 g/mL prior to RNA isolation gave the highest sensitivity, with the detection of two SKMEL28 cells in 5 mL of blood. In addition, the RNA isolation method and the kind of RT enzyme used had a significant impact on the sensitivity and reproducibility of tyrosinase detection, whereas variations in the PCR conditions had only a minor influence. Furthermore, we showed that amplification of MelanA in addition to tyrosinase resulted in an approximately 10% enhanced sensitivity of melanoma cell detection, whereas gp100/pMel17 and MUC18 gene products were also detected in blood from non-melanoma patients. MelanA could serve as a sensitive marker in addition to tyrosinase for detecting micrometastases.

Amplification of MelanA messenger RNA in addition to tyrosinase increases sensitivity of melanoma cell detection in peripheral blood and is associated with the clinical stage and prognosis of malignant melanoma.

An improved protocol for reverse transcription-polymerase chain reaction (RT-PCR), amplifying tyrosinase and MelanA/MART-1 mRNA from peripheral blood, was used to test 340 blood samples from 225 patients with malignant melanoma for the presence of circulating tumour cells. Positive results for tyrosinase or MelanA were obtained in 19% of patients in stage I (n = 74), 31% in stage II (n = 45), 29% in stage III (n = 48) and 52% in stage IV (n = 58). Amplification of MelanA in addition to tyrosinase resulted in a 30% enhanced sensitivity of melanoma cell detection compared with amplification of tyrosinase alone. The sensitivity was further enhanced by analysis of at least two blood samples per patient and performing at least two PCR analyses per sample. During a median follow-up of 4 months, patients with a positive PCR showed a 2. 4-fold increased risk for relapse compared with PCR-negative patients. These data indicate that the detection of circulating melanoma cells in peripheral blood using our optimized protocol for RT-PCR correlated with the clinical stage of disease and is therefore likely to be a prognostic marker for recurrence. MelanA is a sensitive additional marker to tyrosinase in detecting micrometastases using RT-PCR.

Detection of melanoma micrometastasis in sentinel nodes by reverse transcription-polymerase chain reaction correlates with tumor thickness and is predictive of micrometastatic disease in the lymph node basin.

The sentinel node has been reported to be representative for the presence or absence of metastatic melanoma in the draining lymph node basin. In this study, for the first time sentinel nodes and adjoining nonsentinel nodes were analyzed for micrometastatic disease using tyrosinase reverse transcription-polymerase chain reaction (RT-PCR) in comparison with standard immunohistochemistry. Successful identification of the sentinel nodes using a gamma probe-guided surgery was achieved in 73 (92%) of 79 patients with cutaneous stage I and II melanoma (tumor thickness > or =0.75 mm). A total of 794 regional lymph nodes, 148 sentinel nodes, and 646 adjoining nonsentinel nodes were evaluated. Tyrosinase RT-PCR was shown to increase the sensitivity for melanoma cell detection in sentinel nodes significantly (49% positivity) as compared with immunohistochemistry using antibodies against HMB-45 antigen and S-100 protein (18% positivity). Examination of sentinel nodes was highly predictive in determining the presence of regional lymph node micrometastasis by immunohistochemistry (99%) and RT-PCR (89%). Interestingly, detection of nodal micrometastasis by RT-PCR showed a strong positive correlation with tumor thickness of primary cutaneous melanoma. These results suggest the clinical significance and emphasize the importance of tyrosinase RT-PCR for detection of melanoma micrometastasis in sentinel nodes.