Metabolic heterogeneity is a key factor in cancer pathogenesis. We found that a subset of BRAF- and NRAS-mutant human melanomas resistant to the MEK inhibitor selumetinib displayed increased oxidative phosphorylation (OxPhos) mediated by the transcriptional coactivator PGC1α. Notably, all selumetinib-resistant cells with elevated OxPhos could be resensitized by cotreatment with the mTORC1/2 inhibitor AZD8055, whereas this combination was ineffective in resistant cell lines with low OxPhos. In both BRAF- and NRAS-mutant melanoma cells, MEK inhibition increased MITF expression, which in turn elevated levels of PGC1α. In contrast, mTORC1/2 inhibition triggered cytoplasmic localization of MITF, decreasing PGC1α expression and inhibiting OxPhos. Analysis of tumor biopsies from patients with BRAF-mutant melanoma progressing on BRAF inhibitor ± MEK inhibitor revealed that PGC1α levels were elevated in approximately half of the resistant tumors. Overall, our findings highlight the significance of OxPhos in melanoma and suggest that combined targeting of the MAPK and mTORC pathways may offer an effective therapeutic strategy to treat melanomas with this metabolic phenotype.

Recently, five studies in the Nature1, 2, 3, 4, 5 and two studies in the New England Journal of Medicine6, 7 explored the molecular determinants of responsiveness to the inhibition of programmed cell death-l (PD-1), its ligand PD-L1, and cytotoxic T lymphocyte antigen-4 (CTLA-4) for tumour immunotherapy. These prototypical checkpoint inhibitors have taken two decades to advance from discovery to the clinic and to demonstrate that while there has been progress, much remains to be done before we can realise Ehrlich's ‘magic bullet’ to treat all cancers. The first putative case of tumour regression dates back to St Peregrine Laziosi (the ‘Cancer Saint’) in 1320 whose ulcerating cancer eventually healed after it became infected.8 The hypothesis that infection can somehow stir a ‘sleeping’ immune system to control cancer was reinforced by anecdotal reports by Campbell de Morgan who observed cancer remissions in patients with postoperative streptococcal wound infections in 1875, and inconclusively tested by William Coley who developed bacteria-free extracts of streptococci (Coley's toxins) to treat sarcomas from 1881 to 1936. However, it was not until 1957 that MacFarlane Burnet and Lewis Thomas crystallised the immunosurveillance concept that a failure of the immune system to recognise and eliminate transformed neoplastic host tissues might have a central role in cancer pathogenesis (reviewed in Dunn et al.9). This cell-extrinsic theoretical viewpoint was ahead of its time and became overshadowed in the subsequent 50 years by major advances in understanding the cell-intrinsic mechanisms that drive cancer initiation, progression and spread. Utilising this knowledge, drugs designed to specifically target the mutated surface molecules, signalling pathways and gene networks involved in carcinogenesis have revolutionised the treatment of many cancers, with significant improvements in patient outcomes. Unfortunately, these molecularly targeted therapies are often limited by a narrow spectrum of sensitive cancers and the inevitable development of cancer drug resistance. In the past few decades, clinical data showing increased rates of cancers in immunodeficient patients and transplant patients on immunosuppressive drugs, together with divergent results in immunocompetent and immunodeficient mouse models of cancer, have provided additional evidence highlighting the importance of immunosurveillance in cancer pathogenesis.10 Furthermore, studies of the tumour microenvironment have revealed complex dynamic interactions between heterogeneous cancer cell clones and a range of innate and adaptive immune cells including tumour-infiltrating CD8+ cytotoxic T lymphocytes (CTLs), CD4+ helper T lymphocytes, natural killer (NK) cells, NK T cells, tumour-associated macrophages, myeloid-derived suppressor cells, dendritic cells and regulatory T cells. Thus, tumour antigens (altered self) that can be specifically recognised by CTLs are constantly under selective pressure to mutate. In addition, cancers can also actively suppress antitumour immune responses and promote cancer cell growth and metastasis by hijacking the physiological control mechanisms used by the host to enforce peripheral self-tolerance and to dampen chronic inflammation. This Darwinian tug-of-war between cancer and the immune system lead Schrieber and colleagues to propose the cancer immunoediting concept.9 Initial phase I studies have shown efficacy for PD-1–PD-L1 inhibition in metastatic melanoma, renal cell carcinoma and non-small-cell lung cancer.11, 12, 13 It should be noted that only a proportion of patients responded in these trials and patients with castrate-resistant prostate, colorectal, breast, pancreatic and gastric cancers, which are classically considered less immunogenic, did not respond at all. Objective response correlated with PD-L1 expression by the tumour,11 although PD-1 blockade improves survival regardless of PD-L1 expression by the tumour.6 In the current studies, Herbst et al.2 and Tumeh et al.4 now report that PD-L1 expression by immune cells in the tumour microenvironment is also a key predictor of response. Furthermore, it was shown that the infiltration of CTLs with clonally restricted T-cell receptor repertoire and PD-1 and PD-L1 expression by immune cells at the tumour margins correlated with response.4 These and other data point to the presence of a pre-existing immune response held in check by ‘adaptive immune resistance’ in those who respond to checkpoint inhibition. Previous reports have indicated that cancers with high rates of somatic mutations respond better to checkpoint inhibitors, possibly because these cancers are more likely to generate neoantigens that can be recognised by CTLs. Therefore, Yadav et al.5 developed algorithms to predict immunogenic mutations by combining mass spectrometry with whole exome and transcriptome sequencing data in two mouse cancer cell lines. Despite the fact that the screen identified >1300 amino acid substitutions, only a surprisingly small fraction of these mutant peptides was immunogenic when used as a cancer vaccine. These ‘passenger mutations’ were in genes and were not directly involved in carcinogenesis. Interestingly, peptide-major histocompatibility I dextramers used to identify antitumour CTLs also showed that they had an exhausted phenotype and expressed high levels of PD-1 and T-cell immunoglobulin mucin protein-3 (TIM-3). Gubin et al.1 examined a mouse model in which cancers lose neoantigen expression and become resistant to immune rejection. When these mice were treated with anti-PD-1 and anti-CTLA-4, either singly or in combination, they rejected the tumour by recognising two different neoantigens. Vaccinating mice with these escape neoantigens also resulted in tumour rejection. Along similar lines, Snyder et al.7 showed that patients with long-term clinical benefit from anti-CTLA-4 therapy had a high mutation load and that the predicted neoantigen landscape in these patients were dotted with a unique neoepitope signature. Notably, the neoantigens associated with long-term benefit were more likely to be homologous to viral and bacterial antigens than those associated with minimal or no benefit, suggesting that they may originate from memory CTLs. Collectively, these data reveal the tumour microenvironment as a dynamic ecosystem that can be tipped in favour of the host by boosting antitumour immunity (Figure 1). However, despite its success, autoimmune toxicities are sometimes associated with the treatment with checkpoint inhibitors, particularly CTLA-4 inhibitors. So what can be done to further improve antitumour immune responses and minimise toxicity? Other checkpoint inhibitors (such as lymphocyte activation gene-3 and TIM-3), other approaches to cancer immunotherapy including co-stimulatory molecules (such as ICOS, CD40L and GITR), cytokines (such as interleukin-2 and interferon-γ), cancer vaccines, chimeric antigen receptors and other cell-based therapies are being developed, and these may well synergise with checkpoint blockade. Intriguingly, it was recently reported that targeted therapy with selective B-Raf and v-Raf murine sarcoma viral oncogene homolog B (BRAF) inhibitors induced a marked CD4+ and CD8+ T-cell infiltration and upregulated expression of granzyme B in human melanomas.14 These and other data suggest that targeted therapies may cause acute inflammatory cell death and prime the immune system against the tumour, or even directly activate T cells expressing wild-type BRAF. In addition, radiation oncologists have observed rare abscopal effects, whereby localised radiotherapy is associated with regression of metastatic cancers distant from the irradiated site.15 In the most well-documented case, regression was associated with the evidence of a strong immune response against the tumour. Thus, the combination of targeted therapy or radiotherapy and checkpoint inhibition may improve responses in immunogenic cancers and may convert less immunogenic cancers into more immunogenic ones. These observations bring us back to St Peregrine and Coley's toxins—‘the sleeper awakes’! Overcoming adaptive immune resistance with checkpoint inhibitors. The immune system recognises neoantigens generated by somatic mutation to eliminate cancer cells. However, cancers have developed multiple strategies to evade and suppress this antitumour immune response. These include loss of neoantigen expression and hijacking normal control mechanisms used to enforce peripheral self-tolerance (such as CTLA-4-mediated suppression by regulatory T cells) and dampen chronic inflammation (such as PD-1–PD-LI-mediated exhaustion of antitumour CTLs). Checkpoint inhibitors block these inhibitory molecules to drive CTL killing of cancer cells expressing escape neoantigens.

Analysis of 501 melanoma exomes revealed RGS7, which encodes a GTPase-accelerating protein (GAP), to be a tumor-suppressor gene. RGS7 was mutated in 11% of melanomas and was found to harbor three recurrent mutations (p.R44C, p.E383K and p.R416Q). Structural modeling of the most common recurrent mutation of the three (p.R44C) predicted that it destabilizes the protein due to the loss of an H-bond and salt bridge network between the mutated position and the serine and aspartic acid residues at positions 58 as 61, respectively. We experimentally confirmed this prediction showing that the p.R44C mutant protein is indeed destabilized. We further show RGS7 p.R44C has weaker catalytic activity for its substrate Gα_o, thus providing a dual mechanism for its loss of function. Both of these effects are expected to contribute to loss of function of RGS7 resulting in increased anchorage-independent growth, migration and invasion of melanoma cells. By mutating position 56 in the R44C mutant from valine to cysteine, thereby enabling the formation of a disulfide bridge between the two mutated positions, we slightly increased the catalytic activity and reinstated protein stability, leading to the rescue of RGS7's function as a tumor suppressor. Our findings identify RGS7 as a novel melanoma driver and point to the clinical relevance of using strategies to stabilize the protein and, thereby, restore its function.

In this Australian population, LM was twice as frequent as other types of MIS. Improved strategies for diagnosis and management are required.

Accurate staging of patients with primary cutaneous melanoma includes assessment of regional lymph nodes for the presence of micrometastatic disease. Sentinel lymph node biopsy is highly accurate but is an invasive surgical procedure with a 5-10% complication rate, and requires labour-intensive and expensive histological examination to identify disease. A rapid, accurate and cost-effective non-surgical technique able to detect micrometastatic deposits of melanoma in regional lymph nodes would be of great benefit. Fine needle aspiration biopsies and tissue specimens were obtained from lymph nodes from 18 patients undergoing node resection for metastatic melanoma and five patients undergoing radical retropubic prostatectomy. One-dimensional proton magnetic resonance spectroscopy was undertaken at 360 MHz (8.5 T). Lymph nodes were cut into 3 mm thick slices and embedded. Four sequential 5 microm tissue sections were cut from each block and stained, with haematoxylin and eosin, for S100 protein, for HMB45, and again with haematoxylin and eosin, respectively. Proton magnetic resonance spectroscopy distinguished between benign and malignant lymph node tissue (P < 0.001, separate t-test) and benign and malignant lymph node fine needle aspiration biopsy (P < 0.012) based on the ratio of the integrals of resonances from lipid/other metabolites (1.8-2.5 p.p.m. region) and 'choline' (3.1-3.3 p.p.m. region). In conclusion, one-dimensional proton magnetic resonance spectroscopy on a simple fine needle aspiration biopsy can distinguish lymph nodes containing metastatic melanoma from uninvolved nodes, providing a rapid, accurate and cost-effective non-surgical technique to assess regional lymph nodes in patients with melanoma.

In the current study population, IHC-measured pre-treatment BRAF(V600E) protein expression does not predict response or outcome to BRAF inhibitor therapy in BRAF(V600E) metastatic melanoma patients.

Lentigo maligna (LM) incidence is increasing. LM frequently involves the face near critical anatomical structures and as a consequence clinical management is challenging. Nonsurgical therapies, including radiotherapy (RT), are increasingly used. Evidenced-based treatment guidelines are lacking. We conducted a review of previously published data analysing RT treatment of LM. A search of PubMed, Embase and Medline databases to June 2012 identified nine clinical studies that examined the use of RT for LM treatment in at least five patients. Nine studies described 537 patients with LM treated with definitive primary RT, between 1941 and 2009, with a median reported follow-up time of 3 years. Eight articles could be reviewed for oncological outcome data. There were 18 recurrences documented in a total of 349 assessable patients (5%). Salvage was successful in the majority of recurrent LM cases by using further RT, surgery or other therapies. Progression to LM melanoma (LMM) occurred in five patients (five out of 349, 1.4%) who all had poor outcomes. There were five marginal recurrences documented out of 123 assessable patients (4%). There were eight in-field recurrences documented with either LM (five) or LMM (three) out of 171 assessable patients (5%). A series of recommendations were then developed for RT parameters for treatment of LM. These parameters include treatment volume, dose, dose per fraction and outcome measures. These may be of use in prospective data collection.

Our study confirms that paraffin FISH is a sensitive and specific ancillary tool in the diagnosis of BST neoplasms when used in the appropriate clinicopathological context. These findings highlight the need for further ancillary molecular tools in the diagnosis and characterization of challenging cases.

When a progressively growing, symmetrically patterned melanocytic nodule is identified, NM needs to be excluded.

Predicting clinical behavior of atypical Spitz tumors remains problematic. In this study, we assessed interobserver agreement of diagnosis by 13 expert dermatopathologists for atypical Spitz tumors (n=75). We determined which histomorphologic features were most heavily weighted for their diagnostic significance by the experts and also which histomorphologic features had a statistically significant correlation with clinical outcome. There was a low interobserver agreement among the experts in categorizing lesions as malignant versus nonmalignant (κ=0.30). The histomorphologic features that were given the most diagnostic significance by the experts were: consumption of the epidermis, atypical mitoses, high-grade cytologic atypia, and mitotic rate. Conversely, the histomorphologic features that most correlated with disease progression were: frequent mitoses, deep mitoses, asymmetry, high-grade cytologic atypia, and ulceration. The presence and/or pattern of pagetoid spread, consumption of the epidermis, and lymphoid aggregates demonstrated no association with clinical behavior. The results support the assertion that there is a lack of consensus in the assessment of atypical Spitz tumors by expert dermatopathologists. Importantly, many features used to distinguish conventional melanoma from nevi were not useful in predicting the behavior of atypical Spitz tumors. This study may provide some guidance regarding histologic assessment of these enigmatic tumors.