Desmoplastic Melanoma Research Articles

Abstract CT009: S1512: High response rate with single agent anti-PD-1 in patients with metastatic desmoplastic melanoma

Abstract Background: Desmoplastic melanoma (DM) is a subtype of melanoma with high tumor mutation burden (TMB) due to ultraviolet light damage. A previously published retrospective review of patients with PD-1 blockade treated DM suggested this cancer may be highly responsive to PD-1 blockade (Eroglu et al. Nature 2018). S1512 is the first prospective study investigating PD-1 blockade with pembrolizumab in patients with DM. 1512 Cohort A results were presented and demonstrated a 59% complete pathologic response rate with neoadjuvant pembrolizumab in patients with resectable DM (Kendra et al. ASCO 2022). Herein, we present results from S1512 Cohort B in patients with metastatic DM. Experimental procedures: Patients aged ≥18 with metastatic DM received pembrolizumab 200 mg q3 weeks. Eligibility criteria included: Zubrod PS 0-2, no central nervous system metastases, autoimmune disease, or steroid ≥10 mg of prednisone. The primary endpoint was complete response rate (CR) assessed per RECIST 1.1, with the assumption that CR of 20% or higher indicates that the treatment is of interest. A single stage design with 21 eligible patients would have an alpha of 8.5% (when the true CR is 5%) and a power of 82%. Tumor assessments were performed every 9 weeks. Secondary endpoints included progression free survival (PFS), overall survival (OS), and toxicity assessment. Biopsies were analyzed by whole exome sequencing (WES) for mutational load and oncogenic driver mutations. Summary of data: 27 eligible patients were enrolled in Cohort B. 93% were male, 70% had Zubrod PS 0, median age 75 (range 59-90). Median number of cycles received: 15 (range 1-34). At the time of data cutoff, 3 patients remain on protocol treatment with pembrolizumab. Treatment was discontinued due to: 2 years of therapy (4), adverse event (AE) (8), physician and patient choice (6), progressive disease (4), and under review (2). Objective response rate (including both confirmed and unconfirmed partial and complete responses) was 85% (95% CI: 66%-96%), with 7/27 CR (26%) and 16/27 PR (59%). Grade 3 or higher adverse events were reported in 10 patients. WES analysis was available for 16 patients. Both baseline (N=10) and on-treatment biopsies (N=12) were evaluated for canonical genetic drivers of melanoma; 7 patients had tumors with loss of function (LOF) mutations in NF1, and all had mutations in TP53, with no case having activating mutations in BRAF or NRAS, consistent with the known genetic alterations in DM. The median TMB in baseline biopsies was 79.4 Mut/Mb (range 34.3-159). Conclusion: Patients with metastatic DM are exceptional responders to single agent PD-1 blockade with pembrolizumab. Based on this data, the pathologic subtype of melanoma can be used as a predictive biomarker of response to single agent pembrolizumab. Funding: U10CA180888 and U10CA180819; and in part by Merck Sharp & Dohme LLC., a subsidiary of Merck & Co., Inc., Rahway, NJ, USA Citation Format: Kari Kendra, Shay Bellasea, Zeynep Eroglu, Siwen Hu-Lieskovan, Katie M. Campbell, William Carson, David Wada, Jose A. Plaza, Jeffrey Sosman, Gino K. IN, Alexandra Ikeguchi, John Hyngstrom, Andres Brohl, Nikhil I. Khushalani, Joseph Markowitz, George Negrea, Samer Kasbari, Gary C. Doolittle, Umang Swami, Toni Roberts, Sapna P. Patel, Elad Sharon, James Moon, Michael C. Wu, Antoni Ribas. S1512: High response rate with single agent anti-PD-1 in patients with metastatic desmoplastic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT009.

Top 10 Differential Diagnoses for Desmoplastic Melanoma.

Desmoplastic melanoma is a rare subtype of melanoma mainly appearing on sun-exposed skin. Clinically, it is many times non-pigmented and therefore the diagnosis is often not suspected. Review article. In this paper we review the main histopathological, immunohistochemical, and molecular features of desmoplastic melanoma, as well as the top 10 morphologic differential diagnoses which should be considered in most cases. The histopathological pattern can be many times deceptive, mimicking a scar, a fibrous reaction, a fibrohistiocytic tumor such as a dermatofibroma, a vascular tumor such as angiosarcoma, a smooth muscle tumor such as leiomyosarcoma, or a neural tumor. Although an overlying atypical junctional melanocytic proliferation may be seen in most cases, it is absent in a significant percentage (up to 30%) of cases, making the diagnosis even more difficult in those instances. The range of diagnostic pitfalls is wide, which may present disastrous prognostic consequences. Desmoplastic melanoma is often a difficult diagnosis to make, as it frequently shows nonspecific clinical findings and overlapping histologic features with many other tumors. However, the potential clinical and prognostic consequences of misdiagnosis as another entity are great. Therefore, this diagnosis must always be kept in mind when encountering spindle cell tumors affecting the head and neck area.

Local Recurrence Rates After Excision of Desmoplastic Melanoma: A Systematic Review and Meta-Analysis.

Few prospective studies have evaluated local recurrence rates (LRR) after excision of desmoplastic melanoma (DM); however, several retrospective studies have reported high LRR. To determine LRR after excision of DM and evaluate factors affecting LRR. Systematic review of the PubMed, Embase, and Web of Science databases was performed to identify studies reporting local recurrence after excision of DM with conventional wide local excision (WLE), Mohs micrographic surgery (MMS), or staged excision (SE). Meta-analysis was performed to calculate summary LRR and pooled risk ratios (RR). Literature search identified 4 studies evaluating MMS or SE (total n = 61 DM). 53 studies assessed WLE ( n = 3,080) and were analyzed quantitatively. The overall LRR after WLE of DM was 21% (95% CI, 0.16-0.28; n = 2,308). Local recurrence rate was higher with positive/unknown histologic excision margins (49%, 95% CI, 0.25-0.74; n = 91) versus negative histologic margins (11%, 95% CI, 0.07-0.17; n = 1,075; [ p < .01]). Neurotropism was also associated with increased LRR (RR, 1.79; 95% CI, 1.34-2.38, p < .01; n = 644). DM has high LRR after WLE. Local recurrence risk was greatest with positive excision margins, indicating the importance of achieving negative microscopic margins. Greater study of MMS and SE for DM is required.

Tertiary lymphoid structures in desmoplastic melanoma have increased lymphocyte density, lymphocyte proliferation, and immune cross talk with tumor when compared to non-desmoplastic melanomas

ABSTRACT Tertiary lymphoid structures (TLS) are ectopic lymphoid structures that can arise in human cancers and are associated with improved overall survival (OS) and response to immune checkpoint blockade (ICB) in several cancers, including non-desmoplastic metastatic melanoma (NDMM). Desmoplastic melanoma (DM) has one of the highest response rates to ICB, and we previously identified that primary DM (PDM) contains TLS. Despite the association of TLS with survival and ICB response, it is unknown whether TLS or associated markers of immune activity can differ between PDM and NDMM. We hypothesized that PDM would contain higher frequencies of TLS than NDMM, that T and B-cell densities and proliferation would be greater in TLS of PDM than TLS of NDMM, and that proliferation rates of T and B-cells in PDM TLS would be concordant with those of intratumoral lymphocytes. We found that four features of TLS in PDM distinguish them from TLS in NDMM. TLS were peritumoral in NDMM but intratumoral in PDM. CD8+ T-cell and CD20+ B-cell densities and proliferative fractions were higher in PDM TLS than NDMM TLS. Additionally, the proliferative fractions of T- and B-cells were concordant between the TLS and tumor site in PDM and discordant in NDMM. Collectively, these data suggest that TLS and associated immune markers can differ across melanoma subsets and suggest that PDM TLS may be more immunologically active and have enhanced immune cell trafficking between tumor and TLS compared to NDMM.

Representativeness of initial skin biopsies showing pure desmoplastic melanoma: implications for management

Desmoplastic melanoma (DM) is an uncommon subtype of melanoma with distinct clinicopathological features. It is classified into pure desmoplastic melanoma (PDM) when the proportion of desmoplastic melanoma is ≥90% of the dermally-invasive component, and mixed desmoplastic melanoma (MDM) when the proportion of desmoplastic melanoma is <90%. Studies have reported a lower sentinel lymph node biopsy (SLNB)-positivity rate in PDM compared to MDM and non-DM. As a result, some have recommended not performing SLNB in PDM patients. When PDM is identified in a partial biopsy of a melanoma, there is a risk that sampling bias may under-recognise MDM, but to the best of our knowledge this has not been previously assessed or quantified. The aim of this study was to assess the concordance of the proportion of desmoplastic melanoma in an initial partial biopsy of PDM with the proportion in the entire tumour following complete excision, in patients with cutaneous melanoma. A secondary aim was to determine how frequently this potentially resulted in a patient not receiving a SLNB. Seventy-eight cases of cutaneous melanoma were identified from the Melanoma Institute Australia (MIA) database and 23 cases from the Memorial Sloan Kettering Cancer Centre (MSKCC), where an initial biopsy contained PDM and a subsequent wide excision had residual invasive melanoma. Clinicopathological features were analysed in all patients, including whether a SLNB was performed, the results of SLNB, and any subsequent recurrence. Ninety percent (91/101) of cases were still classified as PDM in the complete wide excision specimen while 10% (10/101) of cases were reclassified as MDM, which was a significant change in classification of final desmoplastic melanoma subtype (p<0.001). The proportion of desmoplastic melanoma was also significantly different between the initial and excisional biopsies (p=0.004). Forty-eight (48/101) patients had a SLNB, of which two (4.5%) were positive for metastatic melanoma; both cases were PDM in the excision specimen. Of the 10 cases demonstrating MDM in the excision specimen, the initial biopsy was a punch biopsy in six cases, shave biopsy in two cases and subcutaneous tissue was sampled in two patients (one punch biopsy, one incisional biopsy). Four of these 10 patients underwent SLNB which was negative in all cases. Twenty-two patients developed recurrence in the follow-up period (median 30 months, range 1-192 months), three with MDM in their excision specimen. One patient did not have a SLNB and developed regional lymph node recurrence. In this study there was a 10% risk that the percentage of desmoplastic melanoma in an initial biopsy of PDM was not representative of the entire lesion, resulting in reclassification as MDM in the excision specimen. If a SLNB is not performed in such cases, a positive SLNB may be missed (one patient in our study) which could impact treatment options for the patient. We recommend caution in not offering a SLNB in the setting of an initial biopsy of PDM if the biopsy is small compared with the overall lesion. If a SLNB is not procured at the time of wide excision in such cases, the SLNs should still be mapped by lymphoscintigraphy to facilitate careful follow up and to enable earlier detection and treatment of nodal disease.

Interobserver agreement in the histopathological classification of desmoplastic melanomas

Desmoplastic melanoma is a subtype of melanoma characterised by amelanotic fusiform melanocytes dispersed in a collagenous stroma. Cell-poor and fibrous stroma-rich 'pure' variants have been distinguished from 'mixed' variants with areas of higher cell density and/or less desmoplastic stroma. This distinction is relevant because patients whose tumours display a pure phenotype have a lower risk for regional lymph node metastasis and distant recurrence. However, little is known about interobserver agreement among pathologists in the subclassification of desmoplastic melanoma. To address this issue, we conducted a study in which eleven dermatopathologists independently evaluated whole slide scanned images of excisions from 30 desmoplastic melanomas. The participating pathologists were asked to classify the tumours as pure or mixed. They were also asked to record the presence or absence of neurotropism and angiotropism. We found substantial interobserver agreement between the 11 dermatopathologists in the classification of tumours as pure versus mixed desmoplastic melanoma (kappa=0.64; p<0.0001). There was fair agreement between the 11 dermatopathologists in the evaluation of presence versus absence of neurotropism (kappa=0.26; p<0.0001), and slight agreement in the assessment of angiotropism (kappa=0.13; p<0.0001). The level of concordance in the subclassification of desmoplastic melanomas is encouraging for the acceptance of this prognostic parameter in the real-world practice of melanoma pathology.

Next-generation Sequencing as a Potential Diagnostic Adjunct in Distinguishing Between Desmoplastic Melanocytic Neoplasms.

Desmoplastic melanomas (DMs) are often challenging to diagnose and ancillary tests, such as immunohistochemistry, have limitations. One challenge is distinguishing DM from benign desmoplastic melanocytic neoplasms. In this study, we explored the utility of next-generation sequencing data in the diagnosis of DMs versus desmoplastic Spitz nevi (DSN) and desmoplastic nevi (DN). We sequenced 47 cases and retrieved 12 additional previously sequenced clinical cases from our dermatopathology database. The 59 total cases were comprised of 21 DMs, 25 DSN, and 13 DN. The DMs had the highest tumor mutation burden at 22 mutations/megabase (m/Mb) versus the DSN (6m/Mb) and DN (8m/Mb). Truncating mutations in NF1 resulting in a loss-of-function were exclusive to the DM cohort, identified in 8/21 (38%) cases. Importantly, missense mutations in NF1 were nonspecific and seen with similar frequency in the different cohorts. Other mutations exclusive to the DMs included truncating mutations in TP53 , CDKN2A , and ARID2 . Among the DSN, 17/25 (68%) had an HRAS mutation or receptor tyrosine kinase fusion consistent with other Spitz tumors. Two cases in the DN cohort had missense mutations in BRAF without additional progression mutations and 2 other cases had mutations in GNAQ , supporting a diagnosis of a sclerosing blue nevus. The remainder of the DN had nonspecific mutations in various signaling pathways with few progression mutations. Overall, our study provides preliminary data that next-generation sequencing data may have the potential to serve as an ancillary diagnostic tool to help differentiate malignant and benign desmoplastic melanocytic neoplasms.

PRAME is a useful marker for the differential diagnosis of melanocytic tumours and histological mimics.

Although the morphological assessment of melanoma is generally straightforward, diagnosis can be especially difficult when the significant morphological and immunohistochemical results overlap with those of benign and malignant melanocytic tumours and histological mimics. This study assessed the potential diagnostic utility of measuring PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemically in naevi, melanomas and clear cell sarcomas (CCSs) in Chinese patients. We examined the immunohistochemical expression of PRAME in 317 melanocytic naevi, 178 primary melanomas, 72 metastatic melanomas and 19 CCSs and compared the sensitivity and specificity of PRAME immunohistochemistry (IHC) in the differential diagnosis of melanocytic tumours and histological mimics. Of the 317 melanocytic naevi, 98.1%were completely negative for PRAME; six cases showed focal PRAME immunoreactivity in a minor population of lesional melanocytes. Diffuse nuclear immunoreactivity for PRAME was found in 89.9% of primary melanomas and 93.1% of metastatic melanomas. Regarding melanoma subtypes, PRAME was expressed in 100% of superficial spreading melanomas, 100% of melanomas arise in congenital naevus, 91.4% of nodular melanomas, 87.8% of acral lentigo melanomas, 80.0% of lentigo malignant melanomas, 60.0% of Spitz melanomas, 96.2% of mucosal melanomas and 80.0% of uveal melanomas. None of the two desmoplastic melanomas expressed PRAME. Of the 19 CCS cases, 89.5% were negative for PRAME and 10.5% showed focal weak PRAME immunoreactivity in a minor population of tumour cells. Our findings indicate that PRAME may be a useful marker to support a suspected diagnosis of melanoma. In addition, lack of PRAME expression is a valuable hint to CCS in a suspected case, and then molecular confirmation of the presence of EWSR1 rearrangement is necessary.

PRAME Immunoexpression in 275 Cutaneous Melanocytic Lesions: A Double Institutional Experience.

In recent years, the preferentially expressed antigen in melanoma (PRAME) has also been used in the histopathological diagnosis of melanocytic lesions, in order to understand if it could constitute a valid, inexpensive, and useful resource in dermatopathological fields. We performed a double-center study to evaluate whether the data on the usefulness and possible limitations of PRAME could also be confirmed by our group. From 1 December 2021 to 29 March 2022, we collected 275 cases of melanocytic lesions that were immunostained with PRAME (Ab219650) and rabbit monoclonal antibody (Abcam). To better correlate the PRAME expression with its nature (benign, uncertain potential for malignancy, or malignant), we categorized PRAME tumor cells’ percentage positivity and intensity of immunostaining in a cumulative score obtained by adding the quartile of positive tumor cells (0, 1+, 2+, 3+, 4+) to the PRAME expression intensity in tumor cells (0, 1+, 2+, 3+). Of these 275 lesions, 136 were benign, 12 were of uncertain potential for malignancy (MELTUMP or SAMPUS or SPARK nevus), and 127 were malignant. The immunoexpression of PRAME was completely negative in 125/136 benign lesions (91.9%), with only a few positive melanocytes (1+) and intensity 1+ in the remaining 11 cases (8.1%). Of the 127 cases of melanoma (superficial spreading, lentigo maligna, and pagetoid histotypes), PRAME was strongly positive in 104/127 cases (81.8%) with intensity 4+ and 3+. In 17 cases (13.3%; melanoma spindle and nevoid cell histotypes), PRAME was positive in percentage 2+ and with intensity ranging from 2+ to 3+. In 7 cases (5.5%) of desmoplastic melanoma, PRAME was 1+ positive and/or completely negative. Of the 12 cases of lesions with uncertain potential for malignancy, the immunoexpression of PRAME was much more heterogeneous and irregularly distributed throughout the lesion. These data are perfectly in agreement with the current literature, and they demonstrate that the reliability of PRAME is quite high, but its use cannot cause physicians to disregard the morphological information and the execution of other ancillary immunohistochemical stains such as Melan-A, HMB-45, MiTF, and SOX-10.

Current and future approaches in the surgical management of T3b/T4 primary and locoregionally advanced melanoma.

Currently accepted principles of surgical management-margin width, use of sentinel node biopsy, performance of radical node dissections for node-positive cases-and some aspects of postoperative management (use of radiation for desmoplastic melanoma primaries and for clinically node-positive disease) will change in the future with the potential widespread adoption of adjuvant and neoadjuvant therapies.

Does the morphology of cutaneous melanoma help to explain the international differences in survival? Results from 1 578 482 adults diagnosed during 2000–2014 in 59 countries (CONCORD-3)

BackgroundCONCORD‐3 highlighted wide disparities in population‐based 5‐year net survival for cutaneous melanoma during 2000–2014. Clinical evidence suggests marked international differences in the proportion of lethal acral and nodular subtypes of cutaneous melanoma.ObjectivesWe aimed to assess whether the differences in morphology may explain global variation in survival.MethodsPatients with melanoma were grouped into the following seven morphological categories: malignant melanoma, not otherwise specified (International Classification of Diseases for Oncology, third revision morphology code 8720), superficial spreading melanoma (8743), lentigo maligna melanoma (8742), nodular melanoma (8721), acral lentiginous melanoma (8744), desmoplastic melanoma (8745) and other morphologies (8722–8723, 8726–8727, 8730, 8740–8741, 8746, 8761, 8770–8774, 8780). We estimated net survival using the nonparametric Pohar Perme estimator, correcting for background mortality by single year of age, sex and calendar year in each country or region. All‐ages survival estimates were standardized using the International Cancer Survival Standard weights. We fitted a flexible parametric model to estimate the effect of morphology on the hazard of death.ResultsWorldwide, the proportion of nodular melanoma ranged between 7% and 13%. Acral lentiginous melanoma accounted for less than 2% of all registrations but was more common in Asia (6%) and Central and South America (7%). Overall, 36% of tumours were classified as superficial spreading melanoma. During 2010–2014, age‐standardized 5‐year net survival for superficial spreading melanoma was 95% or higher in Oceania, North America and most European countries, but was only 71% in Taiwan. Survival for acral lentiginous melanoma ranged between 66% and 95%. Nodular melanoma had the poorest prognosis in all countries. The multivariable analysis of data from registries with complete information on stage and morphology found that sex, age and stage at diagnosis only partially explain the higher risk of death for nodular and acral lentiginous subtypes.ConclusionsThis study provides the broadest picture of distribution and population‐based survival trends for the main morphological subtypes of cutaneous melanoma in 59 countries. The poorer prognosis for nodular and acral lentiginous melanomas, more frequent in Asia and Latin America, suggests the need for health policies aimed at specific populations to improve awareness, early diagnosis and access to treatment. What is already known about this topic? The histopathological features of cutaneous melanoma vary markedly worldwide.The proportion of melanomas with the more aggressive acral lentiginous or nodular histological subtypes is higher in populations with predominantly dark skin than in populations with predominantly fair skin. What does this study add? We aimed to assess the extent to which these differences in morphology may explain international variation in survival when all histological subtypes are combined.This study provides, for the first time, international comparisons of population‐based survival at 5 years for the main histological subtypes of melanoma for over 1.5 million adults diagnosed during 2000–2014.This study highlights the less favourable distribution of histological subtypes in Asia and Central and South America, and the poorer prognosis for nodular and acral lentiginous melanomas.We found that later stage at diagnosis does not fully explain the higher excess risk of death for nodular and acral lentiginous melanoma compared with superficial spreading melanoma.

Desmoplastic melanoma treated with wide local excision or Mohs micrographic surgery: Rates of positive margins, local recurrence, and repeat surgeries

To the Editor: Desmoplastic melanoma (DM) treated with wide local excision (WLE) has high rates of positive margins1,2 and local recurrence,3 leading to repeat surgeries. Mohs micrographic surgery (MMS) may confirm clear margins before reconstruction and reduce recurrence; however, published cohorts of MMS for DM have been small.4 We examined the surgical outcomes of DMs treated with WLE or MMS in the largest published cohort of DMs treated with MMS.

Diagnostic utility of PRAME, p53 and 5-hmC immunostaining for distinguishing melanomas from naevi, neurofibromas, scars and other histological mimics

High expression of PRAME (PReferentially expressed Antigen in MElanoma) and p53 (a proposed marker of desmoplastic melanoma) and low expression of 5-hydroxymethylcytosine (5-hmC) have each been reported in melanoma. However, their combined diagnostic utility for distinguishing melanomas, including uncommon variants, from histological mimics is unknown. This study sought to determine the utility of PRAME, p53 and 5-hmC immunostains for diagnosing melanocytic tumours. A total of 333 cutaneous melanocytic tumours (melanoma n=280, naevi n=53), 20 cutaneous neurofibromas, and 15 scars were evaluated using multiplex immunofluorescence (n=313) or single-plex chromogenic immunohistochemical staining (n=55). Immunostaining for PRAME and 5-hmC were each scored using a previously described semiquantitative scale 0 (absent) to 4+ (diffuse). p53 was scored using a previously described immunoreactive score (range 0-300). PRAME expression was significantly higher in melanomas than in naevi (p<0.0001), with the lowest PRAME expression found in low-grade desmoplastic melanomas compared to the other melanoma subtypes. In non-desmoplastic melanomas, 38% showed 4+ staining (>75% positive tumour cells) and 70% showed 3+ or 4+(>50% positive tumour cells). Conversely, 96% of naevi showed 0, 1+ or 2+ expression. 5-hmC expression was significantly lower in melanomas than in naevi (p<0.0001). However, acral melanomas were not significantly associated with loss of 5-hmC expression (p=0.84). Compared with using PRAME in isolation, combining PRAME and 5-hmC scores increased sensitivity (64%-84%) for detecting melanoma. With respect to desmoplastic melanoma compared to scar or neurofibroma, strong PRAME or p53 staining were almost exclusively found in high-grade desmoplastic melanomas; low-grade desmoplastic melanomas, neurofibromas and scars were negative. 5-hmC was not useful in distinguishing desmoplastic melanomas from neurofibromas or scars. Our data support the use of PRAME as a highly specific ancillary investigation in the diagnosis of melanoma, however PRAME should be considered 'positive' if there is 3+ or 4+ staining (rather than the widely recommended 4+ threshold). 5-hmC, PRAME and p53 appear to have a limited role in the diagnosis of low-grade desmoplastic melanomas.

PRAME expression is similar in scar and desmoplastic melanoma.

PRAME expression is similar in scar and desmoplastic melanoma.

Immunohistochemistry in melanocytic lesions: Updates with a practical review for pathologists.

This review provides a summary of the immunohistochemical markers pertinent to the diagnosis of melanocytic lesions. There is considerable morphologic overlap between benign and malignant melanocytic lesions, and given the significant differences in clinical management, the diagnostic workup becomes crucial. Immunohistochemistry aids in the distinction between various melanocytic proliferations and recent contributions to the literature have furthered our optimization of panels in the diagnostic workup. In recent years, SOX10 has been considered as the optimal marker for melanocytic lesions given the similar sensitivity but higher specificity than S100. HMB-45 is less sensitive than S100 but demonstrates utility in confirmation of deceptively banal small cell and nevoid melanoma variants where deep nests of melanocytes are highlighted. Melan-A (MART-1) and MiTF show similar sensitivity to S100 however there is a lack of expression in spindle cell and desmoplastic melanomas.

Neoadjuvant PD-1 blockade in patients with resectable desmoplastic melanoma (SWOG 1512).

9502 Background: Desmoplastic melanoma (DM) is a rare cancer defined by a dense fibrous collagen matrix. It is associated with high UV exposure leading to a high mutational load. When locally advanced, the standard of care is wide excision and radiation therapy due to its propensity for local relapses. Metastatic DM has a high response rate (RR) to PD-1 blockade therapy (Eroglu et al. Nature 2018). We hypothesized that neoadjuvant treatment with anti-PD-1 monotherapy may induce pathologically confirmed regressions in a high percentage of cases, potentially allowing for less extensive local treatment. Methods: Patients &gt; 18 years old with histologically confirmed resectable (primary, recurrent, or regional lymph node metastasis) DM with clinical evidence of residual disease received pembrolizumab 200 mg q3 weeks (wk) 3 followed by excision. No adjuvant therapy was administered. Primary endpoint: pathological complete response (pCR), with the assumption that pCR of 25% would be considered a positive result worthy of future study. To test this hypothesis, a single arm trial with 25 eligible patients would have a 3.4% probability of a positive result with a true pCR of 5%, and a power of 90% of a positive result if the true pCR is 25%. Secondary endpoints: clinical RR by imaging and clinical exam, median overall survival (OS), and evaluation of safety/tolerability of neoadjuvant pembrolizumab. Adverse events were assessed q3 wk. Disease assessments occurred at baseline and q9 wk. NCT02775851. Results: We enrolled-29 eligible patients with resectable DM. One patient refused treatment and was omitted from further analysis. Median age was 75, 79% were male, primary sites of disease were 72% H&amp;N, 10% torso, 14% extremities, 3% unknown. No patients received prior systemic therapy. Mean time from C1D1 treatment to surgery was 84.2 (range: 52-135) days, mean number of cycles received 3.3 (range: 2-4). 26/27 (93%) of patients underwent wide excision of the resectable disease, of which 14 (54%) underwent sentinel lymph node biopsy. One patient underwent resection of a nodal recurrence thus did not require wide excision. pCR was noted in 15/27 (56%) of patients (95% CI: 35%-75%). One patient without a pCR had a major pathologic response with 0.2 mm residual melanoma. In addition, one patient with a clinical CR did not undergo resection by choice. None became inoperable. Clinical RR was 52% (95% CI: 32%-71%). Median OS has not been reached, with two nontreatment related deaths (acute hypoxic respiratory failure; unknown). No &gt; grade 2 related adverse events were observed. Conclusions: Neoadjuvant pembrolizumab in resectable DM results in a high pCR rate with excellent tolerance, which supports consideration of PD-1 blockade therapy prior to surgery. Funding: U10CA180888 and U10CA180819; and in part by Merck Sharp &amp; Dohme Corp., a subsidiary of Merck &amp; Co., Inc., Kenilworth, NJ, USA. Clinical trial information: NCT02775851.

The Expression of Connexin 37, 40, 43, 45 and Pannexin 1 in the Early Human Retina and Choroid Development and Tumorigenesis.

The expression pattern of Connexins (Cx) 37, 40, 43, 45 and Pannexin 1 (Pnx1) was analyzed immunohistochemically, as well as semi-quantitatively and quantitatively in histological sections of developing 8th- to 12th-week human eyes and postnatal healthy eye, in retinoblastoma and different uveal melanomas. Expressions of both Cx37 and Cx43 increased during development but diminished in the postnatal period, being higher in the retina than in the choroid. Cx37 was highly expressed in the choroid of retinoblastoma, and Cx43 in epitheloid melanoma, while they were both increasingly expressed in mixoid melanoma. In contrast, mild retinal Cx40 expression during development increased to strong in postnatal period, while it was significantly higher in the choroid of mixoid melanoma. Cx45 showed significantly higher expression in the developing retina compared to other samples, while it became low postnatally and in all types of melanoma. Pnx1 was increasingly expressed in developing choroid but became lower in the postnatal eye. It was strongly expressed in epithelial and spindle melanoma, and particularly in retinoblastoma. Our results indicate importance of Cx37 and Cx40 expression in normal and pathological vascularization, and Cx43 expression in inflammatory response. Whereas Cx45 is involved in early stages of eye development, Pnx1might influence cell metabolism. Additionally, Cx43 might be a potential biomarker of tumor prognosis.

Hypopigmented variant of intraoral common blue nevus. A rare entity

<h3>Objectives</h3> Blue nevus (BN) represents a clinicopathologically distinctive subset of benign melanocytic proliferations that may affect the oral mucosa. While diagnosis of conventional BN is usually straightforward, some of its rare variants may cause significant overlap with other entities, causing diagnostic pitfalls. Herein we present a case of hypopigmented variant of common BN and discuss the diagnostic challenges. <h3>Findings</h3> A 52 year-old male of unremarkable medical history was referred for the evaluation of a painless palatal lesion of unknown duration. The clinical examination revealed a well-circumscribed, slightly elevated lesion of normal hue with bluish halo involving the hard palate. With a provisional diagnosis of BN an excisional biopsy was decided. Histopathologically, a proliferation composed of scattered elongated, finely branching melanocytes, located deeply within the lamina propria with non-infiltrating pattern and associated with a variably desmoplastic stroma, was observed. Cytoplasmic pigmentation was detected only in a small subset of dendritic processes after serial sectioning. Minimal cytologic atypia and mild nuclear pleomorphism were also present in the absence of mitotic activity. In order to rule out malignant melanocytic tumors, especially desmoplastic melanoma, extensive immunohistochemical examination was performed. Melanocytes were strongly and diffusely positive for Melan-A, HMB-45, SOX-10, S-100, p16, and vimentin. The proliferation index Ki-67 was <5%. A final diagnosis of hypopigmented common BN was rendered. No signs of recurrence were noted during follow-up. <h3>Conclusions</h3> To this date, few cases of BN with minimal or absent pigmentation have been reported in the literature. However, this pattern is extremely rare in lesions affecting the oral mucosa. Hypopigmented BN lesions require careful evaluation to be distinguished primarily from desmoplastic melanoma. Immunohistochemistry may be helpful, especially when tumors with atypia, pleomorphism, infiltrative pattern and/or mitoses are encountered.

A Diagnostic Challenge: Desmoplastic Melanoma

Desmoplastic melanoma (DM) is uncommon and can be a diagnostic challenge both clinically and histologically. We report a unique presentation of DM presenting as an amelanotic, depressed, indurated plaque on the forehead. The lesion was clinically concerning for a morpheaform basal cell carcinoma and with an unrevealing initial punch biopsy, an excisional biopsy with IHC was necessary to determine a diagnosis of pure desmoplastic melanoma. When a patient presents with a depressed, indurated plaque of unknown etiology, including DM in the clinical differential diagnosis and communicating this to the dermatopathologist can potentially reduce the risk for a delay in diagnosis.

WITHDRAWN: Update on the Diagnosis and Management of Desmoplastic Melanoma

The Publisher regrets that this article is an accidental duplication of an article that has already been published, https://doi.org/10.1016/j.ad.2021.06.013 . The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal