Management of early melanoma recurrence despite adjuvant anti-PD-1 antibody therapy☆.

BACKGROUND: Anti-programmed cell death protein 1 (PD-1) antibodies (PD1) prolong recurrence-free survival in high-risk resected melanoma; however, approximately 25%-30% of patients recur within 1 year. This study describes the pattern of recurrence, management and outcomes of patients who recur with adjuvant PD1 therapy. PATIENTS AND METHODS: Consecutive patients from 16 centres who recurred having received adjuvant PD1 therapy for resected stage III/IV melanoma were studied. Recurrence characteristics, management and outcomes were examined; patients with mucosal melanoma were analysed separately. RESULTS: Melanoma recurrence occurred in 147 (17%) of ∼850 patients treated with adjuvant PD1. In those with cutaneous melanoma (n = 136), median time to recurrence was 4.6 months (range 0.3-35.7); 104 (76%) recurred during (ON) adjuvant PD1 after a median 3.2 months and 32 (24%) following (OFF) treatment cessation after a median 12.5 months, including in 21 (15%) who ceased early for toxicity. Fifty-nine (43%) recurred with locoregional disease only and 77 (57%) with distant disease. Of those who recurred locally, 22/59 (37%) subsequently recurred distantly. Eighty-nine (65%) patients received systemic therapy after recurrence. Of those who recurred ON adjuvant PD1, none (0/6) responded to PD1 alone; 8/33 assessable patients (24%) responded to ipilimumab (alone or in combination with PD1) and 18/23 (78%) responded to BRAF/MEK inhibitors. Of those who recurred OFF adjuvant PD1, two out of five (40%) responded to PD1 monotherapy, two out of five (40%) responded to ipilimumab-based therapy and 9/10 (90%) responded to BRAF/MEK inhibitors. CONCLUSIONS: Most patients who recur early despite adjuvant PD1 develop distant metastases. In those who recur ON adjuvant PD1, there is minimal activity of further PD1 monotherapy, but ipilimumab (alone or in combination with PD1) and BRAF/MEK inhibitors have clinical utility. Retreatment with PD1 may have activity in select patients who recur OFF PD1.

Five-year survival outcomes for patients with advanced melanoma treated with pembrolizumab in KEYNOTE-001.

BACKGROUND: Pembrolizumab demonstrated robust antitumor activity and safety in the phase Ib KEYNOTE-001 study (NCT01295827) of advanced melanoma. Five-year outcomes in all patients and treatment-naive patients are reported herein. Patients whose disease progressed following initial response and who received a second course of pembrolizumab were also analyzed. PATIENTS AND METHODS: Patients aged ≥18 years with previously treated or treatment-naive advanced/metastatic melanoma received pembrolizumab 2 mg/kg every 3 weeks, 10 mg/kg every 3 weeks, or 10 mg/kg every 2 weeks until disease progression, intolerable toxicity, or patient/investigator decision to withdraw. Kaplan-Meier estimates of overall survival (OS) and progression-free survival (PFS) were calculated. Objective response rate and PFS were based on immune-related response criteria by investigator assessment (data cut-off, September 1, 2017). RESULTS: KEYNOTE-001 enrolled 655 patients with melanoma; median follow-up was 55 months. Estimated 5-year OS was 34% in all patients and 41% in treatment-naive patients; median OS was 23.8 months (95% CI, 20.2-30.4) and 38.6 months (95% CI, 27.2-not reached), respectively. Estimated 5-year PFS rates were 21% in all patients and 29% in treatment-naive patients; median PFS was 8.3 months (95% CI, 5.8-11.1) and 16.9 months (95% CI, 9.3-35.5), respectively. Median response duration was not reached; 73% of all responses and 82% of treatment-naive responses were ongoing at data cut-off; the longest response was ongoing at 66 months. Four patients [all with prior response of complete response (CR)] whose disease progressed during observation subsequently received second-course pembrolizumab. One patient each achieved CR and partial response (after data cut-off). Treatment-related AEs (TRAEs) occurred in 86% of patients and resulted in study discontinuation in 7.8%; 17% experienced grade 3/4 TRAE. CONCLUSIONS: This 5-year analysis of KEYNOTE-001 represents the longest follow-up for pembrolizumab to date and confirms the durable antitumor activity and tolerability of pembrolizumab in advanced melanoma. CLINICAL TRIAL REGISTRY: ClinicalTrials.gov, NCT01295827.

How melanoma cells evade trail-induced apoptosis.

At the doses used clinically, chemotherapy is believed to kill melanoma by a final common 'mitochondrial' pathway that leads to apoptosis. Similarly, several natural defence mechanisms kill melanoma by the same pathways. A corollary to the latter is that survival of melanoma in the host is due to the development of anti-apoptotic mechanisms in melanoma cells. What are these mechanisms? And how might we bypass them to improve the treatment of melanoma?

Societal preference values for advanced melanoma health states in the United Kingdom and Australia.

BACKGROUND: No studies measure preference-based utilities in advanced melanoma that capture both intended clinical response and unintended toxicities associated with treatment. METHODS: Using standard gamble, utilities were elicited from 140 respondents in the United Kingdom and Australia for 13 health states. RESULTS: Preferences decreased with reduced treatment responsiveness and with increasing toxicity. CONCLUSIONS: These general population utilities can be incorporated into treatment-specific cost-effectiveness evaluations.

O(6)-methylguanine-DNA methyltransferase depletion and DNA damage in patients with melanoma treated with temozolomide alone or with lomeguatrib.

We evaluated the pharmacodynamic effects of the O(6)-methylguanine-DNA methyltransferase (MGMT) inactivator lomeguatrib (LM) on patients with melanoma in two clinical trials. Patients received temozolomide (TMZ) for 5 days either alone or with LM for 5, 10 or 14 days. Peripheral blood mononuclear cells (PBMCs) were isolated before treatment and during cycle 1. Where available, tumour biopsies were obtained after the last drug dose in cycle 1. Samples were assayed for MGMT activity, total MGMT protein, and O(6)-methylguanine (O(6)-meG) and N7-methylguanine levels in DNA. MGMT was completely inactivated in PBMC from patients receiving LM, but detectable in those on TMZ alone. Tumours biopsied on the last day of treatment showed complete inactivation of MGMT but there was recovery of activity in tumours sampled later. Significantly more O(6)-meG was present in the PBMC DNA of LM/TMZ patients than those on TMZ alone. LM/TMZ leads to greater MGMT inactivation, and higher levels of O(6)-meG than TMZ alone. Early recovery of MGMT activity in tumours suggested that more protracted dosing with LM is required. Extended dosing of LM completely inactivated PBMC MGMT, and resulted in persistent levels of O(6)-meG in PBMC DNA during treatment.

Biomarkers in melanoma.

Biomarkers are tumour- or host-related factors that correlate with tumour biological behaviour and patient prognosis. High-throughput analytical techniques--DNA and RNA microarrays--have identified numerous possible biomarkers, but their relevance to melanoma progression, clinical outcome and the selection of optimal treatment strategies still needs to be established. The review discusses a possible molecular basis for predictive tissue biomarkers such as melanoma thickness, ulceration and mitotic activity, and provides a list of promising new biomarkers identified from tissue microarrays that needs confirmation by independent, prospectively collected clinical data sets. In addition, common predictive serum biomarkers--lactate dehydrogenase, S100B and melanoma-inhibiting activity--as well as selected investigational serum biomarkers such as TA90IC and YKL-40 are also reviewed. A more accurate, therapeutically predictive classification of human melanomas and selection of patient populations that would profit from therapeutic interventions are among the major challenges expected to be addressed in the future.

Utility of adjuvant systemic therapy in melanoma.

The lack of effective drugs in stage IV melanoma has impacted the effectiveness of adjuvant therapies in stage II/III disease. To date, chemotherapy, immunostimulants and vaccines have been used with minimal success. Interferon (IFN) has shown an effect on relapse-free survival (RFS) in several clinical trials; however, without a clinically significant effect on overall survival (OS). A recently conducted meta-analysis demonstrated prolongation of disease-free survival (DFS) in 7% and OS benefit in 3% of IFN-treated patients when compared with observation-only patients. There were no clear differences for the dose and duration of treatment observed. Observation is still an appropriate control arm in adjuvant clinical trials. Regional differences exist in Europe in the adjuvant use of IFN. In Northwest Europe, IFN is infrequently prescribed. In Central and Mediterranean Europe, dermatologists commonly prescribe low-dose IFN therapy for AJCC stage II and III disease. High-dose IFN regimens are not commonly used. The population of patients that may benefit from IFN needs to be further characterised, potentially by finding biomarkers that can predict response. Such studies are ongoing.

Small molecules and targeted therapies in distant metastatic disease.

Chemotherapy, biological agents or combinations of both have had little impact on survival of patients with metastatic melanoma. Advances in understanding the genetic changes associated with the development of melanoma resulted in availability of promising new agents that inhibit specific proteins up-regulated in signal cell pathways or inhibit anti-apoptotic proteins. Sorafenib, a multikinase inhibitor of the RAF/RAS/MEK pathway, elesclomol (STA-4783) and oblimersen (G3139), an antisense oligonucleotide targeting anti-apoptotic BCl-2, are in phase III clinical studies in combination with chemotherapy. Agents targeting mutant B-Raf (RAF265 and PLX4032), MEK (PD0325901, AZD6244), heat-shock protein 90 (tanespimycin), mTOR (everolimus, deforolimus, temsirolimus) and VEGFR (axitinib) showed some promise in earlier stages of clinical development. Receptor tyrosine-kinase inhibitors (imatinib, dasatinib, sunitinib) may have a role in treatment of patients with melanoma harbouring c-Kit mutations. Although often studied as single agents with disappointing results, new targeted drugs should be more thoroughly evaluated in combination therapies. The future of rational use of new targeted agents also depends on successful application of analytical techniques enabling molecular profiling of patients and leading to selection of likely therapy responders.

Immunotherapy of distant metastatic disease.

Immunotherapy of metastatic melanoma consists of various approaches leading to specific or non-specific immunomodulation. The use of FDA-approved interleukin (IL)-2 alone, in combination with interferon alpha, and/or with various chemotherapeutic agents (biochemotherapy) is associated with significant toxicity and poor efficacy that does not improve overall survival of 96% of patients. Many studies with allogeneic and autologous vaccines have demonstrated no clinical benefit, and some randomised trials even showed a detrimental effect in the vaccine arm. The ongoing effort to develop melanoma vaccines based on dendritic cells and peptides is driven by advances in understanding antigen presentation and processing, and by new techniques of vaccine preparation, stabilisation and delivery. Several agents that have shown promising activity in metastatic melanoma including IL-21 and monoclonal antibodies targeting cytotoxic T lymphocyte-associated antigen 4 (anti-CTLA-4) or CD137 are discussed. Recent advances of intratumour gene transfer technologies and adoptive immunotherapy, which represents a promising although technically challenging direction, are also discussed.

Western blot analysis of antigens on melanoma cells recognized by cytotoxic T cells.

Antigens recognized by cloned cytotoxic T lymphocytes (CTLs) from patients with melanoma were examined by methods based on the ability of antigens immobilized on nitrocellulose paper to stimulate proliferation of the CTLs. The proliferative response depended on the presence of histocompatible antigen-presenting cells (APCs) in the cultures in the form of either autologous lymphoid cell lines (Epstein-Barr virus-transformed B cells) or histocompatible peripheral blood lymphocytes and was maximal at 3 days. Presentation appeared to be via class II major histocompatibility complex antigens, in that monoclonal antibodies (MAbs) against the class II antigens, but not the class I antigens, on the APCs inhibited the proliferative responses. The response the CTLs appeared to be mediated by interaction with the alpha beta CD3 T-cell receptor complex, in that pretreatment of the CTL clones with MAbs against CD3 inhibited the response of these clones to the antigen extracts irrespective of the phenotypes of the clones. Extracts from several nonmelanoma cells did not stimulate CTL clones specific for melanoma. At least two different specificities were detected in extracts from autologous and allogeneic tumor cells. The specificity of proliferative responses by CD3+ CD4+ and CD3+ CD8+ CTLs appeared to be similar to their cytotoxic activity, but CTLs with the CD3+ CD16+ CD8+- phenotype had wider cytotoxic activity against target cells not stimulating proliferative responses. The antigen(s) responsible for the stimulation were shown in all instances to have a molecular mass of 48 kilodaltons. Preliminary analysis suggested that the antigen(s) have both protein and glycolipid (ganglioside) components.

Prognostic significance of leukocyte-dependent antibody activity in melanoma patients.

Sera from patients with melanoma and control subjects were examined for leukocyte-dependent antibody (LDA) activity against cultured melanoma and control nonmelanoma target cells in 51Cr release cytotoxicity assays. In over a third of 344 melanoma patients, LDA activity against melanoma cells was related to tumor growth, shown by disappearance of the LDA after surgical removal of melanoma. Tumor-related LDA activity was not detected in 143 controls with various nonmelanoma malignant conditions and benign skin lesions. Approximately 5% of the patients had high-titer melanoma LDA that was unchanged by surgical removal of the tumor, and 15% had melanoma LDA revealed in their sera only after the sera had been treated to dissociate immune complexes. In patients with stage I melanoma, the disease-free interval was significantly longer in those with tumor-related LDA compared to those with no LDA. Analysis of the data in relation to known prognostic variables suggested that the main influence of LDA on prolongation of the disease-free interval was in males. An association between tumor-related LDA and a longer disease-free interval was also apparent in patients with stage II melanoma at first presentation but not in those with recurrence after prior treatment of primary melanoma. The results suggest that LDA activity against melanoma cells in the sera of patients after surgical removal of stage I or stage II melanoma is a favorable prognostic factor. Further studies are needed to determine whether induction of melanoma LDA by immunotherapy may improve the outcome in patients without naturally occurring LDA.

Relationship between natural killer cell activity and histological features of lymphocyte infiltration and partial regression of the primary tumor in melanoma patients.

A group of 194 melanoma patients with Stage I melanoma was studied in an attempt to correlate histological features of prognostic importance in malignant melanoma with the level of natural killer cell (NK) activity in blood mononuclear cells. Histological features examined were lymphocytic infiltrate of the tumor base, lymphocyte infiltration at the tumor margin, and evidence of partial regression in the tumor. NK activity against melanoma cells and non-melanoma cells was studied in the same patients before and after surgical removal of melanoma. Patients with high NK activity against melanoma and Chang cells had less lymphocyte infiltrate at the base of the tumor irrespective of its thickness than did those with low NK activity. Patients with low NK activity and thin tumors had more lymphocyte infiltration at the base of the tumor than did those with high NK activity. Similar results were obtained in certain subsets of cases with respect to lymphocytic infiltration at the tumor margins and to the presence of partial regression. Although the nature of the association between these histological features and NK activity in blood is unknown, it is suggested that previously unexplained associations between histological features and prognosis may be accounted for by their association with NK activity. If this proves to be correct, measurement of NK activity may be an important additional prognostic factor in patients with melanoma.

Potentiation of lymphocyte responses by monoclonal antibodies to the ganglioside GD3.

Previous studies have shown that the ganglioside GD3 is expressed in high concentrations on melanoma cells and that monoclonal antibodies (MAbs) against GD3 may induce partial remissions in tumor growth in patients with melanoma. The present studies indicated that incubation of interleukin 2 (IL2) dependent murine natural killer cells with several MAbs against the ganglioside GD3 potentiated the proliferative response to IL2. There was no effect on cell division in the absence of added IL2. Similarly the mitogenic response of human blood lymphocytes to phytohemagglutinin (PHA) or the T3 antigen was enhanced by coculture with these MAbs. This was noted when the MAbs to GD3 were added either before or up to 48 h after addition of PHA or MAb to T3. Kinetic analysis revealed that the potentiation of the PHA induced mitogenic response followed the expected response to PHA suggesting that the MAbs amplified normal activation pathways. These effects were also seen wih MAb to GD3 and the T10 structure on T-cells but not with MAbs to the transferrin receptor or isotype MAb controls. Studies on T-cell subsets suggested that the enhanced PHA responses were confined mainly to the T8 subset and responses of the T4 subset were not enhanced. Flow cytometric analysis revealed low levels of GD3 expression on blood lymphocytes which increased during culture with PHA. IL2 receptor (Tac epitope) expression did not show close correlation with the enhanced lymphocyte responses and the mechanism of the potentiation remains uncertain. These studies raise questions concerning the role of gangliosides in T-cell activation and whether these in vitro effects of MAbs to GD3 may account in part for their antitumor effects in patients with melanoma.

Relation of TNF-related apoptosis-inducing ligand (TRAIL) receptor and FLICE-inhibitory protein expression to TRAIL-induced apoptosis of melanoma.

Past studies have shown that apoptosis mediated by TNF-related apoptosis-inducing ligand (TRAIL) is regulated by the expression of two death receptors [TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2] and two decoy receptors (TRAIL-R3 and TRAIL-R4) that inhibit apoptosis. In previous studies, we have shown that TRAIL but not other members of the tumor necrosis factor family induce apoptosis in approximately two-thirds of melanoma cell lines. Here, we examined whether the expression of TRAIL-R at the mRNA and protein level in a panel of 28 melanoma cell lines and melanocytes correlated with their sensitivity to TRAIL-induced apoptosis. We report that at least three factors appear to underlie the variability in TRAIL-induced apoptosis. (a) Four of nine cell lines that were insensitive to TRAIL-induced apoptosis failed to express death receptors, and in two instances, lines were devoid of all TRAIL-Rs. Southern analysis suggested this was due to loss of the genes for the death receptors. (b) Despite the presence of mRNA for the TRAIL-R, some of the lines failed to express TRAIL-R protein on their surface. This was evident for TRAIL-R1 and more so for the TRAIL decoy receptors TRAIL-R3 and -R4. Studies on permeabilized cells revealed that the receptors were located within the cytoplasm and redistribution from the cytoplasm may represent a posttranslational control mechanism. (c) Surface expression of TRAIL-R1 and -R2 (but not TRAIL-R3 and -R4) showed an overall correlation with TRAIL-induced apoptosis. However, certain melanoma cell lines and clones were relatively resistant to TRAIL-induced apoptosis despite the absence of decoy receptors and moderate levels of TRAIL-R1 and -R2 expression. This may indicate the presence of inhibitors within the cells, but resistance to apoptosis could not be correlated with expression of the caspase inhibitor FLICE-inhibitory protein. mRNA for another TRAIL receptor, osteoprotegerin, was expressed in 22 of the melanoma lines but not on melanocytes. Its role in induction of apoptosis remains to be studied. These results appear to have important implications for future clinical studies on TRAIL.

Tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis of human melanoma is regulated by smac/DIABLO release from mitochondria.

In previous studies we have shown that the sensitivity of melanoma cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis was determined largely by the level of expression of death receptor TRAIL receptor 2 on the cells. However, approximately one-third of melanoma cell lines were resistant to TRAIL, despite expression of high levels of TRAIL receptor 2. The present studies show that these cell lines had similar levels of TRAIL-induced activated caspase-3 as the TRAIL-sensitive lines, but the activated caspase-3 did not degrade substrates downstream of caspase-3 [inhibitor of caspase-activated DNase and poly(ADP-ribose) polymerase]. This appeared to be due to inhibition of caspase-3 by X-linked inhibitor of apoptosis (XIAP) because XIAP was bound to activated caspase-3, and transfection of XIAP into TRAIL-sensitive cell lines resulted in similar inhibition of TRAIL-induced apoptosis. Conversely, reduction of XIAP levels by overexpression of Smac/DIABLO in the TRAIL-resistant melanoma cells was associated with the appearance of catalytic activity by caspase-3 and increased TRAIL-induced apoptosis. TRAIL was shown to cause release of Smac/DIABLO from mitochondria, but this release was greater in TRAIL-sensitive cell lines than in TRAIL-resistant cell lines and was associated with down-regulation of XIAP levels. Furthermore, inhibition of Smac/DIABLO release by overexpression of Bcl-2 inhibited down-regulation of XIAP levels. These results suggest that Smac/DIABLO release from mitochondria and its binding to XIAP are an alternative pathway by which TRAIL induces apoptosis of melanoma, and this pathway is dependent on the release of activated caspase-3 from inhibition by XIAP and possibly other inhibitor of apoptosis family members.

MART-1 is expressed less frequently on circulating melanoma cells in patients who develop distant compared with locoregional metastases.

PURPOSE: Polymerase chain reaction (PCR) with tyrosinase and with MART-1 permits detection of small numbers of circulating melanoma cells (CMCs) in patients who have undergone surgical resection of localized disease. In a previous study, we showed that PCR with MART-1 had sensitivity and specificity similar to those of PCR with tyrosinase in terms of detection of CMCs but that PCR with MART-1 seemed to identify a different but overlapping subgroup of patients. In the current study, we examined the utility and prognostic significance of PCR with tyrosinase and with MART-1. PATIENTS AND METHODS: We analyzed the prognostic significance of the patterns of expression of tyrosinase and MART-1 in 186 patients followed sequentially before and after surgical removal of American Joint Committee on Cancer stage I, II, or III melanoma. RESULTS: PCR with tyrosinase and with MART-1 in the first 3 months after surgery identified 68.5% of 73 patients who developed recurrence in the 2-year period after surgery. Approximately 35% of patients with positive tests remained disease-free at 2-year follow-up. We found that patients with disseminated recurrence had a significantly lower incidence of MART-1-positive CMCs (16%) than of tyrosinase-positive CMCs (63%). Patients with locoregional metastases had CMCs that expressed tyrosinase and MART-1 at similar rates. These differences in expression of the markers in patients with disseminated recurrence were also associated with a much lower disease-free survival, in those who had CMCs that were positive for tyrosinase but negative for MART-1. The reverse applied in those with locoregional disease. CONCLUSION: These findings suggest that PCR with MART-1 and with tyrosinase identifies subgroups of patients who develop disseminated or locally recurrent metastases. We hypothesize that immune responses against MART-1 may reduce the establishment of disseminated metastases.

Polymerase chain reaction detection of melanoma cells in the circulation: relation to clinical stage, surgical treatment, and recurrence from melanoma.

PURPOSE: The detection of melanoma cells in the circulation by polymerase chain reaction (PCR) assays has been shown by several investigators to correlate with the stage of the disease and possibly with prognosis. PATIENTS AND METHODS: We performed prospective studies on 276 patients with primary melanoma and regional lymph node (LN) metastases to assess the predictive value of PCR detection of tyrosinase and melanoma antigen recognized by T cells-1 (MART-1) in the blood for recurrence of melanoma. RESULTS: PCR tests for gp 100, Muc-18, and p97 reacted with RNA in blood from healthy subjects and were considered unsuitable for patient monitoring. The tests were most frequently positive in the first 3 months after surgery. There were 47 recurrences in 123 patients who had been followed up for 18 months. Assays within 3 months of surgery predicted recurrence from melanoma in 66% of the latter (tests for tyrosinase alone detected 51% and MART-1 alone 21% of the patients). Hence, 34% of recurrences were not predicted by tests in the early postoperative period. This did not appear to be because of marker-negative melanoma because summation of tests over the first year identified 89% of those with recurrent disease. CONCLUSION: Positive tests were recorded in 35% of patients who remained disease free, but it is too early to assess whether these represent false-positive results. The false-negative results raise the question of whether the assays will provide a reliable basis for selection of patients for adjuvant therapy.

Impediments to successful immunotherapy.

Over the last decade, there has been a considerable increase in understanding of immune responses against cancers, the antigenic structures on tumor cells recognised by the immune system, and the development of more effective vaccines. There is, however, very limited understanding of why the immune system most often fails to control tumor growth and progression. In some patients, it is difficult to demonstrate immune responses to their tumors, and it may be assumed that this reflects poor recognition of tumor antigens, induction of anergy in lymphocytes, or suppression of immune responses by tumor-derived factors. In other patients, tumor progression appears to occur despite the presence of antibody or cell-mediated responses. This may indicate selection of tumor cells that have lost tumor antigens or HLA antigens by immune responses against the tumor. Tumor cells may also become resistant to mediators of apoptosis, such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand used by lymphocytes to kill tumor cells. It is suggested that development of effective immunotherapy will need to include strategies that take into account these limitations of immune responses and classification of tumors according to the treatment approach most likely to succeed.

Activation of the extracellular signal regulated kinase (ERK) pathway in human melanoma.

BACKGROUND: Several studies suggest that melanoma may be resistant to treatment because of resistance to apoptosis and that this may be the result of activation of the extracellular signal regulated kinase (ERK1/2) pathway. AIMS: To test this hypothesis by examining the expression of ERK1/2 and its activated form in histological sections of melanoma and its relation to known prognostic features of the disease. MATERIALS/METHODS: Immunohistochemistry with antibodies to ERK1/2 and phosphorylated ERK (p-ERK) was performed on formalin fixed sections from 42 primary melanomas, 38 metastases, and 20 naevi. Fourteen of the primary melanomas were in the radial and 28 in the vertical growth phase. RESULTS: ERK1/2 was widely expressed (100%) in all the (pigmented) lesions studied. p-ERK1/2 expression was much lower in compound (32.4%) and dysplastic (54.5%) naevi than in primary melanoma (nodular 78.8%, superficial spreading 67%) and subcutaneous metastases (76.3%). p-ERK expression was much lower in lymph node metastases (48.5%), suggesting that the microenvironment may influence the activation of ERK. There was a (non-significant) trend for p-ERK expression to be higher in thick (>1.0 mm) versus thin (< or =1.0 mm) melanoma (p = 0.23). There was a trend for overall survival to be related to p-ERK expression in patients with melanoma over 1 mm in thickness. CONCLUSIONS: Expression of activated ERK1/2 in melanocytic lesions appears to be related to malignant potential so that activation of ERK1/2 may be important in melanoma progression. These results provide important histological support for the proposal that inhibition of this signalling pathway may be useful in treatment of melanoma.