Comprehensive mutational profiling identifies new driver events in cutaneous leiomyosarcoma.

BACKGROUND: Cutaneous leiomyosarcoma (cLMS) is a rare soft tissue neoplasm, showing smooth muscle differentiation, that arises from the mesenchymal cells of the dermis. To-date, genetic investigation of these tumours has involved studies with small sample sizes and limited analyses that identified recurrent somatic mutations in RB1 and TP53, copy number gain of MYCOD and IGF1R, and copy number loss of PTEN. OBJECTIVES: To better understand the molecular pathogenesis of cLMS, we comprehensively explored the mutational landscape of these rare tumours to identify candidate driver events. METHODS: In this retrospective, multi-institutional study, we performed whole-exome sequencing and RNA sequencing on 38 cases of cLMS. RESULTS: TP53 and RB1 were identified as significantly mutated, thus, represent validated driver genes of cLMS. COSMIC mutational signatures SBS7a/b and DBS1 were recurrent, thus, ultraviolet light exposure may be an aetiological factor driving cLMS. Analysis of significantly recurrent somatic copy number alterations, which represent candidate driver events, found focal (<10Mb) deletions encompassing TP53 and KDM6B, and amplifications encompassing ZMYM2, MYOCD, MAP2K4 and NCOR1. A larger (24 Mb) recurrent deletion encompassing CYLD was also identified as significant. Significantly recurrent broad copy number alterations, involving at least half of a chromosome arm, included deletions of 6p/q, 10p/q, 11q, 12q, 13q and 16p/q, and amplification of 15q. Notably PTEN is located on 10q, RB1 on 13q and IGFR1 on 15q. Fusion gene analysis identified recurrent CRTC1/3::MAML2 fusions, as well as many novel fusions in individual samples. CONCLUSIONS: Our analysis of the largest number of cLMS cases to-date highlights the importance of large cohort sizes and the exploration beyond small targeted gene panels when performing molecular analyses, as it allowed a comprehensive exploration of the mutational landscape of these tumours and identification of novel candidate driver events. It also uniquely afforded the opportunity to compare the molecular phenotype of cLMS with LMS of other tissue types, such as uterine and soft tissue LMS. Given that molecular profiling has resulted in the development of novel targeted treatment approaches for uterine and soft tissue LMS, our study now allows the same opportunities to become available for patients with cLMS.

BRCA1-associated-protein-1 inactivated melanocytic tumours: characterisation of the clinicopathological spectrum and immunohistochemical expression pattern of preferentially expressed antigen in melanoma.

AIMS: BRCA1-associaed protein-1 (BAP1) inactivated tumours (BIMT) are rare melanocytic tumours that may be mistaken for Spitz tumours or melanoma. They occur sporadically or in association with the BAP1 tumour predisposition syndrome (BAP1-TPDS), which may be complicated by uveal or cutaneous melanoma, mesothelioma, basal cell carcinoma and renal cell carcinoma. The aim of this study was to characterise the clinicopathological features and the immunohistochemical expression pattern of preferentially expressed antigen in melanoma (PRAME) of BIMT in a large patient cohort. METHODS AND RESULTS: Ethical approval was obtained, haematoxylin and eosin-stained slides were reviewed, PRAME immunohistochemistry was performed and clinical follow-up was obtained from patient records. Sixty-five BIMT from 38 patients (F:M = 4.4:1) were identified. BIMT were typically located on the trunk and head and neck (median size = 0.5 cm). Seven patients with BAP1-TPDS (range = 16-66 years, median = 25) had multiple BIMT (median = 5), while sporadic BIMT were solitary (median patient age = 39 years). One of seven patients with BAP1-TPDS developed additional malignancies (mesothelioma and cutaneous spindle cell melanoma) and died of complications of mesothelioma. All other patients are alive without recurrence of BIMT (median follow-up = 42 months). BIMT presented as intradermal, nodular aggregates of epithelioid melanocytes with low mitotic activity and moderate to severe cytological atypia in 63% of cases. A background conventional naevus was present in 64%. PRAME immunohistochemistry showed negative or weakly patchy positive staining in all BIMT. CONCLUSIONS: BIMT are more common in a sporadic setting and behave indolently, despite worrying cytological atypia. PRAME immunohistochemistry is a reassuring tool in distinguishing BIMT from melanoma.

Using Nomograms Wisely: Predicting Sentinel Node Positivity in Melanoma.

BACKGROUND: Four externally validated sentinel node biopsy (SNB) prediction nomograms exist for malignant melanoma that each incorporate different clinical and histopathologic variables, which can result in substantially different risk estimations for the same patient. We demonstrate this variability by using hypothetical melanoma cases. METHODS: We compared the MSKCC and MIA calculators. Using a random number generator, 300 hypothetical thin melanoma "patients" were created with varying age, tumor thickness, Clark level, location on the body, ulceration, melanoma subtype, mitosis, and lymphovascular invasion (LVI). The chi-square test was used to detect statistically significant differences in risk estimations between nomograms. Multivariate linear regression was used to determine the most relevant contributing pathologic features in cases where the predictions diverged by > 10%. RESULTS: Of 300 randomly generated cases, 164 were deleted as their clinical scenarios were unlikely. The MSKCC nomogram generally calculated a lower risk than the MIA (p < 0.001). The highest risk score attained for any "patient" using MSKCC calculator was 15% achieved in one of 136 patients (0.7%), whereas using the MIA nomogram, 58 of 136 patients (43%, p < 0.001) had predicted risk >15%. Regression analysis on patients with >10% difference between nomograms revealed LVI (26, p < 0.001), mitosis (14, p < 0.001), and melanoma subtype (8, p < 0.001) were the factors with high coefficients within MIA that were not present in MSKCC. CONCLUSIONS: Nomograms are useful tools when predicting SNB risk but provide risk outputs that are quite sensitive to included predictors.

Histological interpretation of spitzoid tumours: an extensive machine learning-based concordance analysis for improving decision making.

The histopathological classification of melanocytic tumours with spitzoid features remains a challenging task. We confront the complexities involved in the histological classification of these tumours by proposing machine learning (ML) algorithms that objectively categorise the most relevant features in order of importance. The data set comprises 122 tumours (39 benign, 44 atypical and 39 malignant) from four different countries. BRAF and NRAS mutation status was evaluated in 51. Analysis of variance score was performed to rank 22 clinicopathological variables. The Gaussian naive Bayes algorithm achieved in distinguishing Spitz naevus from malignant spitzoid tumours with an accuracy of 0.95 and kappa score of 0.87, utilising the 12 most important variables. For benign versus non-benign Spitz tumours, the test reached a kappa score of 0.88 using the 13 highest-scored features. Furthermore, for the atypical Spitz tumours (AST) versus Spitz melanoma comparison, the logistic regression algorithm achieved a kappa value of 0.66 and an accuracy rate of 0.85. When the three categories were compared most AST were classified as melanoma, because of the similarities on histological features between the two groups. Our results show promise in supporting the histological classification of these tumours in clinical practice, and provide valuable insight into the use of ML to improve the accuracy and objectivity of this process while minimising interobserver variability. These proposed algorithms represent a potential solution to the lack of a clear threshold for the Spitz/spitzoid tumour classification, and its high accuracy supports its usefulness as a helpful tool to improve diagnostic decision-making.

Primary cutaneous NUT carcinoma with BRD4::NUTM1 fusion.

Nuclear protein in testis (NUT) carcinoma, molecularly defined by the NUTM1 gene rearrangement, is most commonly reported in young adults in the sinonasal tract, nasopharynx, or thorax. At these sites, NUT carcinoma is an extremely aggressive malignancy with dismal prognosis. Recently, five cases of primary cutaneous NUT adnexal carcinoma have been reported with BRD3 and NSD3 fusion partners. Although NUT adnexal carcinomas are shown to have metastatic potential, they may behave less aggressively than extracutaneous NUT carcinomas. We report a case of a 59-year-old man who underwent a biopsy of a 3-cm plantar mass, which showed BRD4::NUTM1 fusion. The tumor was a poorly differentiated dermal neoplasm showing cytologic atypia, large vesicular nuclei with prominent nucleoli, conspicuous mitotic activity, and foci of necrosis. Immunohistochemically, the tumor showed positivity for keratins, EMA, SOX10, and NUT, with patchy smooth muscle actin. Molecular testing revealed BRD4::NUTM1 rearrangement. With no alternative primary identified by imaging, a diagnosis of primary cutaneous NUT carcinoma was favored. We hope to contribute to the limited body of knowledge on this entity, with emphasis on recognition as well as studying and defining its prognostic differences from extracutaneous NUT carcinomas.

The clinico-pathological spectrum of plaque-type blue naevi and their potential for malignant transformation.

AIMS: Plaque-type blue naevi are rare melanocytic tumours presenting as large, pigmented plaques at birth or during childhood. There is a risk for malignant transformation, but no larger comprehensive studies exist and the diagnosis is challenging, especially on limited biopsy material. The aim is to describe the clinicopathological features and behaviour of the disease more comprehensively. METHODS AND RESULTS: We retrieved eight plaque-type blue naevi, presenting as large, pigmented plaques (median = 7 cm; range = 3-26) most frequently affecting the scalp (four) followed by the cheek, arm, abdominal wall and gluteal cleft (one each), with a slight female predilection. Median age at time of biopsy was 39.5 years (range = 15-90), but three tumours had been present at birth and one since childhood. Histopathologically, the tumours were poorly circumscribed and composed of cellular fascicles of uniform spindle cells in a background of variably prominent pigmented dendritic cells affecting dermis and subcutaneous tissues. The majority had mutations in GNAQ. One tumour showed malignant transformation, characterised by an expansile nodule of pleomorphic epithelioid melanocytes with rhabdoid morphology, high mitotic activity and areas of necrosis. This patient developed metastatic melanoma to lymph nodes. All patients are alive with a median follow-up of 60 months. CONCLUSION: Plaque-type blue naevi are diagnostically challenging tumours with risk for malignant transformation. Awareness and familiarity with the salient clinicopathological features are necessary for reliable diagnosis, and long-term clinical follow-up is required to monitor for malignant transformation.

PRAME Expression Is a Useful Tool in the Diagnosis of Primary and Metastatic Dedifferentiated and Undifferentiated Melanoma.

Although mostly recognized in the metastatic setting dedifferentiated and undifferentiated melanomas are increasingly recognized as cutaneous and, less commonly, mucosal primary tumors. Their diagnosis is challenging and dependent on sampling and recognition of a conventional melanoma precursor and/or detection of a mutation in a conventional melanoma driver gene. PRAME immunohistochemistry has recently become an important ancillary tool in the separation of melanoma from benign nevi, but no comprehensive studies exist regarding its value in the detection of dedifferentiated and undifferentiated melanomas and their separation from atypical fibroxanthoma and pleomorphic dermal sarcoma, the main differential diagnoses on sun-damaged skin. After retrieval from archival files, we performed PRAME immunohistochemistry on 11 primary and 10 metastatic dedifferentiated and undifferentiated melanomas, 11 atypical fibroxanthomas, and 10 pleomorphic dermal sarcomas. Nuclear staining was assigned extent (ranging from 0 to 4 and reflecting the percentage of PRAME-positive tumor nuclei) and intensity scores (graded as absent, weak, moderate, and strong, with assigned scores ranging from 0 to 3) with combined scores ranging from 0 to 7. Both primary and metastatic dedifferentiated and undifferentiated melanomas showed strong and diffuse nuclear PRAME staining with median combined scores of 7. Strong and diffuse staining was also seen in all conventional melanoma precursors except for desmoplastic melanoma. In contrast, PRAME staining in atypical fibroxanthoma and pleomorphic dermal sarcoma was patchy and weak with median combined scores of 2. Our data emphasize the diagnostic utility of PRAME staining as a first screening tool in the detection and workup of dedifferentiated and undifferentiated melanomas, both in the primary and metastatic settings. PRAME immunohistochemistry is particularly helpful as it is also positive in tumors without a recognizable conventional melanoma precursor and in those associated with desmoplastic melanomas, where PRAME is typically found to be negative.

Low-grade Hidradenocarcinomas: A Clinicopathologic Study of an Unusual Carcinoma That Can Mimic its Benign Counterpart.

Hidradenocarcinomas are rare cutaneous adnexal malignancies with sweat gland differentiation that can show a broad spectrum of histomorphologic appearances, ranging from low to high grade. The diagnosis of low-grade hidradenocarcinoma can be challenging and may be mistaken for benign hidradenomas, especially on superficial and partial samples. We performed a retrospective analysis of 16 low-grade hidradenocarcinomas, obtained from 4 large academic institutions. All neoplasms presented clinically as nodular lesions that ranged in size from 1.5 to 6.0 cm. All patients were adults and their age ranged from 33 to 74 years of age. All cases shared features similar to hidradenomas in the surface and mid portion of the tumors and all tumors had 1 or more histomorphologic clues to malignancy, including the presence of an asymmetric and infiltrative growth pattern (especially at the base of the tumors), perineurial invasion, and a desmoplastic stromal reaction. In the tumors evaluated for immunohistochemistry, the tumor cells were positive for p63, EMA, AE1/AE3, MNF116, and CK7. Three patients underwent sentinel lymph node biopsy, and 2 cases showed metastatic disease to regional lymph nodes. All cases (including the 2 cases that had regional lymph node metastasis), showed no local recurrence or distant metastasis observed after a complete re-excision of the tumors (follow-up range from 6 to 72 mo). Our study highlights the salient clinical and histopathologic features of low-grade hidradenocarcinomas and emphasizes the potential diagnostic pitfalls in distinguishing this entity from other neoplasms. Our results indicate that a combination of thorough histopathologic inspection is necessary to support the diagnosis of this rare neoplasm. These tumors can be exceedingly difficult to diagnose and awareness of the subtle features of low-grade hidradenocarcinoma is of importance are as it remains a diagnostic challenge for practicing pathologists.

Not Waiting to Progress; How the COVID-19 Pandemic Nudged Neoadjuvant Therapy for Stage III Locally Advanced Melanoma Patients.

Background: Early-phase neoadjuvant trials have demonstrated promising results in the utility of upfront immunotherapy in locally advanced stage III melanoma and unresected nodal disease. Secondary to these results and the COVID-19 pandemic, this patient population, traditionally managed through surgical resection and adjuvant immunotherapy, received a novel treatment strategy of neoadjuvant therapy (NAT). Methods: Patients with node-positive disease, who faced surgical delays secondary to COVID-19, were treated with NAT, followed by surgery. Demographic, tumour, treatment and response data were collected through a retrospective chart review. Biopsy specimens were analysed prior to the initiation of NAT, and therapy response was analysed following surgical resection. NAT tolerability was recorded. Results: Six patients were included in this case series; four were treated with nivolumab alone, one with ipilimumab and nivolumab and one with dabrafenib and trametinib. Twenty-two incidents of adverse events were reported, with the majority (90.9%) being classified as grade one or two. All patients underwent surgical resection: three out of six patients following two NAT cycles, two following three cycles and one following six cycles. Surgically resected samples were histopathologically evaluated for the presence of disease. Five out of six patients (83%) had ≤1 positive lymph node. One patient showed extracapsular extension. Four patients demonstrated complete pathological response; two had persisting viable tumour cells. Conclusions: In this case series, we outlined how in response to surgical delays secondary to the COVID-19 pandemic, NAT was successfully applied to achieve promising treatment response in patients with locally advanced stage III melanoma.

Dedifferentiated and undifferentiated melanomas: a practical approach to a challenging diagnosis.

Dedifferentiation, defined as the loss of cellular features of terminal differentiation resulting in a more primitive, unspecialized phenotype, is a rare phenomenon in melanoma and more commonly observed in the metastatic setting than in primary melanomas. The diagnosis of dedifferentiated melanoma poses a significant challenge, and the tumors need to be carefully sampled and worked up to identify any residual morphologic, immunohistochemical, or molecular evidence of their melanocytic lineage. This article reviews our current knowledge of the clinical, histopathological, immunohistochemical, and molecular features of these rare tumors and provides a practical diagnostic approach and discussion of the relevant differential diagnoses and associated diagnostic pitfalls.

Distant metastasis from morphologically low-grade spiradenocarcinoma: A report of two cases.

Malignant tumors arising from benign eccrine spiradenomas are rare. They are divided by morphology into low-grade and high-grade spiradenocarcinomas, with prognosis and metastatic potential closely linked to their histopathologic features. Tumors with low-grade morphology are known for their indolent behavior, with only two reported instances of metastatic spread. We report herein two further low-grade metastatic spiradenocarcinomas resulting in distant metastasis. Both tumors showed a background of a benign spiradenoma and subtle histopathologic signs of malignant transformation, characterized by loss of the dual-cell population, up to moderate cytological atypia and increased mitotic activity. Both patients developed metastases to the lungs years after the initial presentation, and one showed additional lymph nodal disease. We show that even the morphologically low-grade tumors may rarely show more aggressive behavior. Although often challenging, recognition of the morphologically low-grade malignant spiradenocarcinoma and long-term follow-up of the patients are important to detect metastatic disease.

Poorly differentiated cutaneous apocrine carcinomas: histopathological clues and immunohistochemical analysis for the diagnosis of this unusual neoplasm.

Primary cutaneous apocrine carcinoma (PCAC) is a rare cutaneous malignancy that is derived from apocrine glands. Histologically, these tumours can appear well-differentiated where diagnosis should be relatively straightforward. However, occasionally these tumours can exhibit high-grade features, and in such instances the diagnosis can be challenging. A retrospective analysis of 12 cases of poorly differentiated PCAC, obtained from large academic institutions, was performed, and summarised below. Immunohistochemical studies were performed in all cases with antibodies against CK7, p63, CAM 5.2, GCDFP-15, GATA3, CEA, PR, ER, HER2, calponin, SMA, androgen receptor and EMA. All 12 cases were poorly differentiated; however, there were some histopathological clues to the diagnosis of apocrine carcinoma; namely, the presence of focal glandular formation, acrosyringial involvement and the presence of single 'pagetoid' cells within epidermis. All tumours were consistently positive for CK7, GATA3 and GCDFP-15 and negative for p63. The tumours had variable expression of CAM5.2, CEA, ER, PR, HER2, androgen receptor and EMA. In three cases, there was a preservation of the myoepithelial cell layer (with calponin and SMA), which also confirmed the primary cutaneous origin. PCAC is a difficult neoplasm to diagnose, as it can appear identical to metastatic carcinomas. We describe 12 cases of poorly differentiated PCAC, highlighting their salient clinical, histopathological and immunohistochemical features, and discuss the potential diagnostic pitfalls in distinguishing this entity from other malignant neoplasms. Our results indicate that a combination of thorough histological inspection coupled with an adequate battery of immunohistochemical stains is necessary to support the diagnosis of PCAC.

Necrotizing Infundibular Crystalline Folliculitis-A Case Report of a Rare Entity and Review of the Literature.

ABSTRACT: Necrotizing infundibular crystalline folliculitis (NICF) is a rare distinct entity that was introduced in 1999. It typically presents with numerous eruptive waxy papules on the forehead and/or the upper back in adults in their fifth to seventh decade of life. The pathogenesis is unknown to date, but yeast and bacterial infection of the follicular ostia seems to contribute to the development. More recently, NICF has occasionally been observed as a side effect of targeted antitumoral therapy. Histopathologically, NICF is characterized by dilated follicular ostia filled with pale filamentous and birefringent material enclosed by parakeratotic columns of the epidermis and accompanied by a mild superficial inflammatory infiltrate of the dermis. This case report is about a 58-year-old male patient presenting with multiple eruptive keratotic papules on his forehead. Histopathology revealed all classic features of NICF. The case represents a classic example of NICF and is compared with previously published cases that are comprehensively summarized in this article.

Value of Immunohistochemistry to Differentiate Digital Papillary Adenocarcinoma From Acral Hidradenoma With Papillary Structures.

ABSTRACT: Digital papillary adenocarcinoma is a malignant adnexal tumor with a predilection for acral sites. Hidradenoma is a benign solid and cystic sweat gland neoplasm with focal ductal and glandular differentiation and good outcomes. Hidradenomas can occur at acral sites and show papillary structures; for this reason, they are included in the differential diagnosis of digital papillary adenocarcinoma, and immunohistochemistry is a valuable tool in this scenario. We described a case of a 43-year-old man with an epithelial tumor showing papillary structures in the intermediate phalanx of the fourth finger. There was diffuse positivity for p63 and negativity for S100 protein, suggesting that this tumor was an acral hidradenoma with papillary structures.

Association of HPV42 with digital papillary adenocarcinoma and the use of in situ hybridization for its distinction from acral hidradenoma and diagnosis at non-acral sites.

Digital papillary adenocarcinoma (DPAC) is a rare tumor of sweat gland origin that preferentially affects the digits and has the potential to metastasize. Its tumor diagnosis can be difficult. Well-differentiated variants of DPAC can be confused with a benign sweat gland tumor, in particular nodular hidradenoma. With the recent detection of HPV42 DNA in DPAC by next-generation sequence analysis, we reasoned that this association could be used for diagnostic purposes. To this end, we performed in situ hybridization for HPV42 on 10 tumors diagnosed as DPAC as well as 30 sweat gland tumors of various histology types, including 8 acral hidradenomas. All DPAC were positive for HPV42. Positive hybridization signals for HPV42 were seen in both primary and metastatic DPACs. All other tumors and normal tissues were negative. This study confirms the association of HPV42 with the tumor cells of DPAC through in situ hybridization. The positive test result in all lesions of DPAC and lack of detection of HPV42 in any of the acral hidradenomas or other sweat gland tumors examined in this series is encouraging for the potential diagnostic utility of the assay. As documented by two scrotal tumors of DPAC, the in situ hybridization test for HPV42 can also help support the rare occurrence of this tumor at a non-acral site.

Cutaneous Myoepithelial Neoplasms on Acral Sites Show Distinctive and Reproducible Histopathologic and Immunohistochemical Features.

Cutaneous myoepithelial neoplasms are a heterogenous group of neoplasms with mixed tumors typically affecting the head and myoepitheliomas showing a predilection for the extremities. Their malignant counterparts, myoepithelial carcinoma, and malignant mixed tumor are exceptionally rare in the skin, and the morphologic criteria for malignancy are only poorly defined. The aim of the present study was to characterize the clinicopathologic features of myoepithelial neoplasms presenting on acral skin. The clinical and histopathologic features of 11 tumors were recorded, and follow-up was obtained. Immunohistochemistry was performed for S100, SOX10, glial fibrillary acidic protein, keratins, epithelial membrane antigen, p63, p40, smooth muscle actin, desmin, and PLAG1. The tumors mainly affected the feet of adults (range: 26 to 78 y; median: 47 y) with a predilection for the great toe and a male predominance of 1.8:1. Most tumors (91%) displayed a lobular architecture composed of solid and nested growth of epithelioid cells with plasmacytoid features in a myxoid or angiomatous stroma. Scattered cytologic atypia and rare duct differentiation were frequently noted. Three tumors with confluent cytologic atypia, infiltrative growth, and lymphovascular invasion were classified as malignant. By immunohistochemistry, the tumors were positive for S100, SOX10, keratins AE1/AE3, CK5/6 and CK7, and PLAG1. Local recurrence and bilateral pulmonary metastasis were observed in a patient presenting with a histopathologically benign-appearing tumor. Two patients with malignant tumors experienced local recurrences, and 1 developed metastasis to soft tissue, lung, and mediastinal lymph nodes. All patients are currently alive, all but 1 with no evidence of disease after a median follow-up interval of 96 months (range: 2 to 360 mo). In conclusion, acral myoepithelial neoplasms show distinctive and reproducible histopathologic and immunohistochemical features. They are best regarded as a distinctive subset of mixed tumors with features reminiscent of their salivary gland counterparts. While most tumors pursue a benign disease course, histopathologic features appear to be a poor indicator of prognosis.

Tumor MHC Class I Expression Associates with Intralesional IL2 Response in Melanoma.

Cancer immunotherapy can result in lasting tumor regression, but predictive biomarkers of treatment response remain ill-defined. Here, we performed single-cell proteomics, transcriptomics, and genomics on matched untreated and IL2 injected metastases from patients with melanoma. Lesions that completely regressed following intralesional IL2 harbored increased fractions and densities of nonproliferating CD8+ T cells lacking expression of PD-1, LAG-3, and TIM-3 (PD-1-LAG-3-TIM-3-). Untreated lesions from patients who subsequently responded with complete eradication of all tumor cells in all injected lesions (individuals referred to herein as "extreme responders") were characterized by proliferating CD8+ T cells with an exhausted phenotype (PD-1+LAG-3+TIM-3+), stromal B-cell aggregates, and expression of IFNγ and IL2 response genes. Loss of membranous MHC class I expression in tumor cells of untreated lesions was associated with resistance to IL2 therapy. We validated this finding in an independent cohort of metastatic melanoma patients treated with intralesional or systemic IL2. Our study suggests that intact tumor-cell antigen presentation is required for melanoma response to IL2 and describes a multidimensional and spatial approach to develop immuno-oncology biomarker hypotheses using routinely collected clinical biospecimens.

Primary de-differentiated, trans-differentiated and undifferentiated melanomas: overview of the clinicopathological, immunohistochemical and molecular spectrum.

Primary cutaneous and mucosal melanoma shows a wide histological spectrum. The correct diagnosis depends upon the demonstration of melanocytic differentiation by recognition of an associated in-situ component or immunohistochemical evidence of a melanocytic phenotype using conventional melanocytic markers, such as S-100, SOX10, Melan-A and HMB-45. Exceptionally, melanomas lose their melanocytic phenotype, at least focally, and show differentiation towards other lineages. Review of the literature shows that de- and trans-differentiation in melanoma is rare but probably under-recognised and under-reported. These often large and frequently ulcerated tumours affect adults and show a wide anatomical distribution, including mucosal sites, although there is a predilection for sun-damaged skin of the head and neck. Histologically, the tumours are biphasic and contain a pre-existing conventional melanoma. The de-differentiated component closely resembles atypical fibroxanthoma, both morphologically and immunohistochemically. Trans-differentiated melanoma may show rhabdomyosarcomatous or spindle cell carcinomatous features. Undifferentiated melanomas are similar tumours in which the conventional melanoma component is absent. Their diagnosis depends entirely upon the clinical context and identification of a classical melanoma driver gene mutation, i.e. BRAF V600E. The diagnosis of these rare and unusual tumours is challenging, and requires thorough tumour sampling and recognition of the background of a pre-existing but often focal conventional melanoma together with molecular analysis.