Undifferentiated and Dedifferentiated Metastatic Melanomas Masquerading as Soft Tissue Sarcomas: Mutational Signature Analysis and Immunotherapy Response

Undifferentiated Pleomorphic Sarcoma in Children and Young Adults: A Comprehensive Clinicopathologic, Genomic, and Epigenetic Comparison With Adult Counterparts

Undifferentiated pleomorphic sarcoma (UPS) occurs primarily in older adults and remains a diagnosis of exclusion due to its lack of differentiation and specific molecular alterations. Its occurrence in children is rare and controversial, with an unclear relationship to its adult counterpart. In this study, we aimed to investigate a cohort of 6 pediatric undifferentiated pleomorphic sarcoma (P-UPS, mean 10 years old) and 19 young-adult undifferentiated pleomorphic sarcoma (YA-UPS, mean 30 years old) cases by conducting a comprehensive comparative analysis of their clinicopathologic, genomic, and epigenetic features relative to their adult undifferentiated pleomorphic sarcoma counterparts (A-UPS, n = 100). Histologically, P-UPS and YA-UPS exhibited broad morphologic spectrum. The most frequent alterations across all groups were TP53, CDKN2A/B, and ATRX, with no significant differences among subsets. Notably, RB1 alterations were absent in P-UPS, although representing the second most common alteration in YA-UPS (32%) and A-UPS (41%). PTEN alterations were significantly more prevalent in YA-UPS (26%) compared with that in P-UPS (0%) and A-UPS (6%). Deletions in chromosomes 10, 16q, and 13q, along with amplification of 20q, were the most common across all groups. Except for a higher frequency of 17q amplification in P-UPS (33%) and YA-UPS (26%) compared with that in A-UPS (6%), no other arm-level differences were observed. P-UPS showed a lower mean fraction genome altered compared with YA-UPS and A-UPS, whereas all UPS age groups showed a low tumor mutational burden (mean <10 mut/MB). Pathogenic germline variants of high clinical significance (TP53, NF1, MLH1, CHEK2, and BARD1) were observed only in YA-UPS (31%) and A-UPS (12%) cases. By T-distributed stochastic neighborhood embedding and hierarchical clustering of DNA methylation, the majority of P-UPS and a small subset of YA-UPS grouped in a distinct cluster, characterized by a lower genomic index compared to A-UPS. In contrast, most UPS occurring in young adults genomically parallel their older adults' counterparts. P-UPS and YA-UPS cases exhibited a better disease-specific and progression-free survival, compared with A-UPS cases.

Molecular Analysis of Cutaneous Sarcomatoid Neoplasms Frequently Identifies Melanoma Driver Variants

Primary cutaneous neoplasms that lack definitive histologic and immunophenotypic evidence of differentiation are a heterogeneous group of tumors with diverse prognoses and management options. These include undifferentiated and dedifferentiated melanoma (UM/DM), atypical fibroxanthoma (AFX), pleomorphic dermal sarcoma (PDS), and sarcomatoid squamous cell carcinoma. Diagnosis requires careful correlation between the clinicopathologic and molecular features, and the finding of a MAPK pathway variant commonly associated with melanoma may support the diagnosis of melanoma over other tumors in this group. To examine the frequency of typical melanoma-associated MAPK pathway-related variants (BRAF, NRAS, KIT, GNAQ, GNA11) among a cohort of primary cutaneous sarcomatoid neoplasms, we conducted a retrospective analysis of 37 cases of immunohistologically unclassifiable primary cutaneous neoplasms, submitted for targeted NGS analysis. All cases lacked a history of a prior relevant tumor, were negative for melanocytic markers (S100, SOX10, HMB45, and Melan-A), or showed <5% staining with 1 or 2 of these markers. Other lineage markers were negative. We identified typical melanoma driver variants in 7 cases (7/37, 19%), including NRAS (5/37, 14%), KIT (1/37, 3%), and GNAQ (1/37, 3%). There were no significant differences in age, sex, tumor site, or mitotic rate between patients with and without a melanoma driver variant. Melanoma cases were thicker (16.3 vs. 9.25 mm, P=0.041) and more likely to show epithelioid cell phenotype (P=0.008). In our cohort, nearly 20% of patients with immunohistologically unclassifiable cutaneous tumors could be reclassified as having primary UM/DM after molecular testing, thereby opening alternative management pathways.

Myxofibrosarcoma with epithelioid morphology: A clinicopathological study of 44 cases with emphasis on differential diagnosis

AIMS

Epithelioid myxofibrosarcoma (eMFS) is an aggressive morphological variant associated with high rates of local recurrence and metastatic disease. The clinicopathological understanding of this disease is currently limited to a few small case-series.

METHODS AND RESULTS

We reviewed 44 cases of eMFS and classified them based on the presence of focal (< 50%) or diffuse (> 50%) epithelioid morphology and Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) grade. The patients (28 males; 16 females) had a median age of 71 years (range = 14-90 years). The proximal extremity was the most common site (n = 21), followed by the trunk (n = 11), distal extremity (n = nine) and head/neck (n = two). Of cases with known depth of involvement (n = 41), 39 involved the subcutis, one was limited to the dermis and one limited to the skeletal muscle. Most cases (n = 34, 77%) demonstrated diffuse (> 50%) epithelioid morphology and were FNCLCC grade 3 (n = 29, 66%). Follow-up data were available for 22 patients. Two developed local recurrence and 10 developed metastases, frequently to regional lymph nodes. All metastatic tumours had a primary lesion with diffuse epithelioid morphology (P = 0.09). There was no association between grade and recurrent or metastatic disease (P = 0.67 and 0.90, respectively). Three cases initially diagnosed as eMFS, one in the neck and two in the axilla, were found to have NRAS Q61R mutations and a high tumour mutation burden and/or ultraviolet (UV)-light DNA mutational signature.

CONCLUSIONS

These findings suggest that UV-driven malignancies (including melanoma or sarcomatoid squamous cell carcinoma) may histologically mimic eMFS and should be considered in cases of eMFS presenting at atypical anatomical sites.

The Diagnostic Utility of PRAME in Primary Cutaneous Dedifferentiated and Transdifferentiated Melanomas

Melanomas show a wide spectrum of clinical, morphological, immunohistochemical, and molecular features, which can impact treatment and prognosis. Dedifferentiated and transdifferentiated melanomas (DTM) are defined as melanomas which have lost conventional melanocytic morphologic and immunohistochemical features, showing sarcomatous morphology and/or immunohistochemical staining of other cell lineages, and as such, can be mistaken for other entities such as collision tumors and undifferentiated spindle cell tumors. In this series, we highlight the utility of preferentially expressed antigen in melanomas (PRAME) in diagnosing undifferentiated/dedifferentiated melanomas. Case 1 is a lentigo maligna melanoma with dedifferentiation on the scalp of an 85-year-old. Case 2 is a desmoplastic melanoma with leiomyosarcomatous transdifferentiation on the cheek of an 80-year-old. Case 3 is a desmoplastic melanoma with rhabdomyosarcomatous transdifferentiation arising from the temple of an 88-year-old. In all cases, conventional melanocytic immunohistochemical markers were positive in the conventional melanoma and negative in the dedifferentiated/transdifferentiated areas. However, PRAME was positive in both the conventional and dedifferentiated areas with varying intensity. Although PRAME immunoreactivity can be seen in other malignant spindle cell tumors, this study highlights the potential utility of PRAME immunohistochemistry when considering a diagnosis of DTM.

A Comparative Genomic Study of Conventional and Undifferentiated Melanoma

Undifferentiated melanoma, defined as melanoma that has lost all usual phenotypic and immunohistochemical characteristics of conventional melanoma, can pose significant diagnostic challenges. Molecular studies have advanced our understanding of undifferentiated melanoma by demonstrating that a subset of these tumors harbors known melanoma driver alterations in genes such as BRAF, NRAS, and NF1. However, there is a paucity of data describing genetic alterations that may distinguish undifferentiated melanoma from conventional melanoma. In this study, we directly compared the genomic profiles of undifferentiated melanoma to a cohort of conventional melanomas, including 14 undifferentiated melanoma cases (comprised of 2 primary cases, 2 cutaneous recurrences, and 10 metastases) and a cohort of 127 conventional melanomas including primary, recurrent, and metastatic cases. Targeted sequencing of 447 cancer-associated genes was performed, including identification of mutations and copy number alterations. NRAS was the most frequent melanoma driver in undifferentiated melanoma (8/14 cases, 57%), although notably, only 1 undifferentiated melanoma harbored an NRAS Q61R mutation. Compared with the conventional melanoma cohort, undifferentiated melanoma demonstrated statistically significant enrichment of pathogenic activating RAC1 mutations (6/14 total cases, 43%), including P29S (4/6 cases), P29L (1/6 cases), and D11E (1/6 cases). In addition to providing insight into the molecular pathogenesis of undifferentiated melanoma, these findings also suggest that RAS Q61R immunohistochemistry may have limited utility for its diagnosis. The presence of recurrent RAC1 mutations in undifferentiated melanoma is also notable as these alterations may contribute to mitogen-activated protein kinase pathway-targeted therapy resistance. Furthermore, the RAC1 alterations identified in this cohort have been shown to drive a melanocytic to mesenchymal switch in melanocytes, offering a possible explanation for the undifferentiated phenotype of these melanomas.

Update on cutaneous mesenchymal tumors in the 5th edition of WHO classification of skin tumors with an emphasis on new fusion-associated neoplasms

The section on mesenchymal tumors in the 5th edition of WHO classification of skin tumors has undergone several changes, the most important of which is the inclusion of newly identified tumor entities, which will be the main focus of this review article. These specifically include three novel cutaneous mesenchymal tumors with melanocytic differentiation, and rearrangements of the CRTC1::TRIM11, ACTIN::MITF, and MITF::CREM genes as well as EWSR1::SMAD3-rearranged fibroblastic tumors, superficial CD34-positive fibroblastic tumors, and NTRK-rearranged spindle cell neoplasms. Some of the other most important changes will be briefly mentioned as well.

Comprehensive Next Generation Sequencing Reveals that Purported Primary Squamous Cell Carcinomas of the Parotid Gland are Genetically Heterogeneous

Squamous cell carcinoma (SCC) is one of the most common malignancies involving the parotid gland, but it has been recognized that the vast majority of parotid SCC represents metastases, especially from the ipsilateral facial skin. Bona fide primary SCC of the parotid is so rare that it is unclear whether it truly exists at all. We sought to molecularly characterize cases diagnosed as primary parotid gland SCC to see if they possess a unique genetic makeup.We identified cases in our archives which had been diagnosed as primary SCC of the parotid gland. In all cases, metastatic disease was excluded by a thorough history and physical examination. Cases with histologic evidence of a precursor neoplasm (e.g., carcinoma ex-pleomorphic adenoma) were also excluded. Targeted next-generation sequencing (NGS) was attempted on all cases.Six cases diagnosed as primary parotid SCC were identified, arising in 4 males and 2 females ranging from 8 to 73 years (mean, 51.8 years). All cases exhibited keratinization and unequivocal invasion. Four of 6 appeared to be arising from cystically dilated ducts. Five of 6 exhibited well-developed cellular atypia; the remaining case, while cytologically bland, demonstrated perineural invasion. Targeted NGS was successful in 5 of 6 cases. Two SCC harbored several mutations in a mutational profile reminiscent of SCCs seen in other organs. One case harbored YAP1::MAML2, a fusion previously reported in porocarcinoma and other neoplasms. One case harbored IRF2BP2::RUNX2, and presumably represents keratocystoma or SCC ex-keratocystoma. Finally, one case an increase of C > T mutations consistent with ultraviolet damage, suggesting that this case represented a cryptic metastasis from cutaneous SCC.Our analysis did not confirm a unifying genetic signature for purported primary parotid SCC. Indeed, our findings suggest that true primary parotid gland SCC is even rarer than already believed. In our 5 cases with results, NGS findings demonstrated that one was likely a keratocystoma, one a cryptic metastasis from a cutaneous SCC, and one a porocarcinoma, either metastatic or primary. The two remaining cases had complex genotypes reminiscent of SCCs from other sites. This may be the signature of genuine parotid primary SCC, but metastasis from an SCC from another organ cannot be excluded. Accordingly, a diagnosis of primary parotid gland SCC should be viewed with skepticism.

Comparisons of clinical characteristics, treatments, and outcomes among different pathological subtypes of chondrosarcoma in the spine

INTRODUCTION

Spinal chondrosarcoma exhibits higher invasiveness and a worse prognosis compared to chondrosarcoma in the extremities. The prognosis and therapeutic plan vary greatly among different pathological subtypes of chondrosarcoma. This study aimed to analyze the differences in clinical characteristics, molecular features, therapeutic effects, and prognostic factors among the subtypes of chondrosarcoma in the spine.

METHODS

A retrospective review was conducted on 205 patients with spinal chondrosarcoma. The clinical features and immunohistochemical (IHC) markers were compared among the pathological subtypes of chondrosarcoma grade 1, grade 2, grade 3, mesenchymal chondrosarcoma (MCS), dedifferentiated chondrosarcoma (DCS), and clear cell chondrosarcoma (CCCS). Chondrosarcoma grade 1/2/3 are collectively referred to as conventional chondrosarcoma (CCS) for multivariate survival analysis. Univariate and multivariate analyses were performed to investigate independent prognostic factors for overall survival (OS) and recurrence-free survival (RFS) in patients with spinal chondrosarcoma. Furthermore, independent prognostic factors for OS and RFS were identified in CCS and MCS.

RESULTS

MCS patients were younger than the other subtypes. Patients with chondrosarcoma grade 1/2 had better OS than those with chondrosarcoma grade 3, MCS and DCS, while only chondrosarcoma grade 1 patients showed better RFS than chondrosarcoma grade 2/3, MCS and DCS patients. Ki-67 index was higher in chondrosarcoma grade 3, MCS and DCS than chondrosarcoma grade 1/2. The comparison of IHC markers further highlighted the overexpression of P53/MDM2 in MCS and DCS. Gross total resection, including en-bloc and piecemeal resection, significantly improved OS and RFS for CCS patients, while only en-bloc resection significantly improved the prognosis of MCS patients. Chemotherapy appeared to be important for the OS of MCS patients.

CONCLUSION

P53/MDM2 pathway was upregulated in MCS and DCS compared to chondrosarcoma grade 1/2. Radical tumor resection is crucial for the treatment of spinal chondrosarcoma, while MCS patients require further comprehensive treatments perioperatively.

Management of undifferentiated adrenal gland metastases from malignant melanoma: case report

Adrenal gland metastases from malignant melanoma are a common but poorly characterised condition. Their lack of consistent clinical features and poor response to immune checkpoint inhibitors pose a significant diagnostic and therapeutic challenge to practitioners. This case report describes a 78-year-old male with no prior history of melanoma presenting with nonspecific abdominal symptoms and unintentional weight loss who was found to have undifferentiated bilateral adrenal gland metastases from malignant melanoma. Despite ongoing investigations, the primary site of the adrenal gland metastases remained unknown, prompting the consideration of primary adrenal melanoma as a diagnosis. The patient underwent four cycles of treatment with immune checkpoint inhibitors, nivolumab and ipilimumab, followed by maintenance therapy and subsequent adrenal metastasectomy. Despite therapeutic efforts, the patient's tumour was resistant to treatment and became undifferentiated. The patient continued with palliative care until his death, more than three years after the onset of symptoms. The clinical features, pathophysiology, diagnosis, treatment, and prognosis of this patient's disease are discussed in detail to help inform the management of similar cases.

Inflammatory Rhabdomyoblastic Tumor: From a Nebulous Smooth Muscle Neoplasm to a Novel Skeletal Muscle Tumor Subtype

Inflammatory rhabdomyoblastic tumor is a recently introduced name for neoplasms currently included in the World Health Organization classification of soft tissue tumors under the rubric inflammatory leiomyosarcoma. Inflammatory rhabdomyoblastic tumor is an excellent example of how surgical pathologists working in conjunction with tumor biologists can greatly improve tumor classification to the benefit of patients. Over the last 28 years, understanding of this entity has undergone a fascinating evolution. This review serves as a summary of the latest findings in inflammatory rhabdomyoblastic tumor research and a diagnostic manual for the practicing surgical pathologist.

The practical utility of AI-assisted molecular profiling in the diagnosis and management of cancer of unknown primary: an updated review

Cancer of unknown primary (CUP) presents a complex diagnostic challenge, characterized by metastatic tumors of unknown tissue origin and a dismal prognosis. This review delves into the emerging significance of artificial intelligence (AI) and machine learning (ML) in transforming the landscape of CUP diagnosis, classification, and treatment. ML approaches, trained on extensive molecular profiling data, have shown promise in accurately predicting tissue of origin. Genomic profiling, encompassing driver mutations and copy number variations, plays a pivotal role in CUP diagnosis by providing insights into tumor type-specific oncogenic alterations. Mutational signatures (MS), reflecting somatic mutation patterns, offer further insights into CUP diagnosis. Known MS with established etiology, such as ultraviolet (UV) light-induced DNA damage and tobacco exposure, have been identified in cases of dedifferentiated/transdifferentiated melanoma and carcinoma. Deep learning models that integrate gene expression data and DNA methylation patterns offer insights into tissue lineage and tumor classification. In digital pathology, machine learning algorithms analyze whole-slide images to aid in CUP classification. Finally, precision oncology, guided by molecular profiling, offers targeted therapies independent of primary tissue identification. Clinical trials assigning CUP patients to molecularly guided therapies, including targetable alterations and tumor mutation burden as an immunotherapy biomarker, have resulted in improved overall survival in a subset of patients. In conclusion, AI- and ML-driven approaches are revolutionizing CUP management by enhancing diagnostic accuracy. Precision oncology utilizing enhanced molecular profiling facilitates the identification of targeted therapies that transcend the need to identify the tissue of origin, ultimately improving patient outcomes.