Cutaneous apocrine mixed tumor with intravascular tumor deposits: a diagnostic pitfall

SOX10-Internal Tandem Duplications and PLAG1 or HMGA2 Fusions Segregate Eccrine-Type and Apocrine-Type Cutaneous Mixed Tumors

Cutaneous mixed tumors exhibit a wide morphologic diversity and are currently classified into apocrine and eccrine types based on their morphologic differentiation. Some cases of apocrine-type cutaneous mixed tumors (ACMT), namely, hyaline cell-rich apocrine cutaneous mixed tumors (HCR-ACMT) show a prominent or exclusive plasmacytoid myoepithelial component. Although recurrent fusions of PLAG1 have been observed in ACMT, the oncogenic driver of eccrine-type cutaneous mixed tumors (ECMT) is still unknown. The aim of the study was to provide a comprehensive morphologic, immunohistochemical, and molecular characterization of these tumors. Forty-one cases were included in this study: 28 cases of ACMT/HCR-ACMT and 13 cases of ECMT. After morphologic and immunohistochemical characterization, all specimens were analyzed by RNA sequencing. By immunohistochemistry, all cases showed expression of SOX10, but only ACMT/HCR-ACMT showed expression of PLAG1 and HMGA2. RNA sequencing confirmed the presence of recurrent fusion of PLAG1 or HMGA2 in all cases of ACMT/HCR-ACMT, with a perfect correlation with PLAG1/HMGA2 immunohistochemical status, and revealed internal tandem duplications of SOX10 (SOX10-ITD) in all cases of ECMT. Although TRPS1::PLAG1 was the most frequent fusion, HMGA2::WIF1 and HMGA2::NFIB were detected in ACMT cases. Clustering analysis based on gene expression profiling of 110 tumors, including numerous histotypes, showed that ECMT formed a distinct group compared with all other tumors. ACMT, HCR-ACMT, and salivary gland pleomorphic adenoma clustered together, whereas myoepithelioma with fusions of EWSR1, FUS, PBX1, PBX3, POU5F1, and KLF17 formed another cluster. Follow-up showed no evidence of disease in 23 cases across all 3 tumor types. In conclusion, our study demonstrated for the first time SOX10-ITD in ECMT and HMGA2 fusions in ACMT and further refined the prevalence of PLAG1 fusions in ACMT. Clustering analyses revealed the transcriptomic distance between these different tumors, especially in the heterogenous group of myoepitheliomas.

Differential Expression of PLAG1 in Apocrine and Eccrine Cutaneous Mixed Tumors: Evidence for Distinct Molecular Pathogenesis

Cutaneous mixed tumors, also known as chondroid syringomas, are benign adnexal neoplasms that share histomorphologic features with pleomorphic adenomas of the salivary gland. Recent work suggests that the similarity between these 2 tumor types extends to the molecular level because both harbor identical chromosomal rearrangements involving the PLAG1 gene. The resulting nuclear PLAG1 overexpression can be detected by immunohistochemistry and has become a useful diagnostic adjunct for both tumor types. In the skin, however, there are 2 morphologically distinct types of mixed tumor, which have been referred to as apocrine-type cutaneous mixed tumor (AMT) and eccrine-type cutaneous mixed tumor (EMT). Previous studies of PLAG1 expression in cutaneous mixed tumor did not distinguish between these types. Here, we evaluated PLAG1 expression by immunohistochemistry in a cohort of 25 cutaneous mixed tumors stratified by type. PLAG1 was overexpressed in the majority of AMT cases (14 of 16) but in none of the EMT cases (0 of 9). A second gene, HMGA2, known to be upregulated in a subset of salivary gland pleomorphic adenomas, was overexpressed in only 1 case of AMT (1 of 16) and in none of the cases of EMT (0 of 9). Our results indicate that apocrine- and eccrine-type mixed tumors are associated with different pathways of molecular pathogenesis and suggest that the emerging relationship between skin and salivary gland mixed tumors is likely limited to those of apocrine type.

An Overview of Uncommon Cutaneous Malignancies, Including Skin Appendageal (Adnexal) Tumours and Sarcomas

A standardised classification of malignant skin appendageal (adnexal) tumours and sarcomas is required for improved patient management and prognosis. This has been hindered by considerable morphological variation both within and between tumour types, the use of many synonyms for the same tumour types and variation in classification between pathologists. This update uses the improved classification in the 2018 WHO classification of skin tumours as the basis to discuss malignant skin appendageal tumours, sarcomas and cutaneous metastases that regularly present to skin cancer clinicians, multidisciplinary skin cancer teams and tumour boards, with current evidence for management, where appropriate.

Hyaline Cell-Rich Apocrine Mixed Tumor with Cytologic Atypia

Hyaline cell-rich apocrine mixed tumor is relatively rare, and it often possesses atypical cells. Despite the presence of atypical cells, other histopathological features such as well circumscription, smooth border, predominance of bland cells, and no mitotic figures lead to classify these tumors as benign. In addition, no recurrence or metastasis has been reported even when cytologic atypia is identified. Here we report a case of hyaline cell-rich apocrine mixed tumor with cytologic atypia, which did not recur for 14 months after excision.

Clinical and pathological study on mixed tumors of the skin

Mixed tumor of the skin (MTS) is a rare benign tumor of the sweat glands with a reported frequency of 0.01% to 0.098%. The objective of the study is to investigate clinicopathological and immunohistochemical features of mixed tumor of the skin.This was a retrospective study of 21 patients diagnosed with MTS at the Institute of Dermatology and Venereology of Sichuan Provincial People's Hospital from 1980 to 2016. Pathological sections of all cases were reread and the diagnosis was verified.There were 14 males (67%) and 7 females (33%). MTS affected the face. The lesions were skin-colored or lightly red, with no subjective symptoms in most cases. Histopathologically, the tumors consisted of epithelial and interstitial components. The epithelium was mainly composed of cubic or polygonal cells, which can be seen within the tubule-like structures with bilayer epithelium. The inner cells mainly expressed cytokeratin and other epithelial markers. The outer cells expressed epithelial and mesenchymal markers. The outer cells expressed S-100, P63, and glial fibrillary acidic protein. The tumors showed interstitial mucus-like and fibrosis changes, and some parts had cartilage-like changes.Pathological diagnosis is particularly important because the clinical symptoms of MTS lack specificity.

Clear cell nodular hidradenoma involving the lymphatic system: a tumor of uncertain malignant potential or a novel example of "metastasizing" benign tumor?

Exceedingly rare cases of neoplasms with clear-cut histopathologic features of benignity can show locoregional or even distant spread. Such cases can become putative examples of "benign metastasis" when a completely favorable clinical outcome is documented after an adequately long follow-up. We report 8 cases of morphologically benign clear cell nodular hidradenoma (CCNH) with lymphatic involvement. In 5 cases the cutaneous tumor showed small foci of intravascular deposits of neoplastic cells; in 2 cases the cutaneous tumor presented with a synchronous tumor in a regional node; in 1 case a nodal location CCNH was found with no evidence of any primary in the skin. All the cases were treated with conservative surgery and none of them showed disease progression during a follow-up period ranging from 2 to 11 years. These data suggest that in the absence of other histopathologic features of malignancy, lymphatic spread in CCNH can still carry an excellent prognosis and can be therefore considered as an example of "benign metastasis." As the latter concept can be set forth only after an uneventful long-term follow-up, in routine practice, cases of morphologically benign CCNH with lymphatic involvement are best labeled "atypical CCNH," or "CCNH-like tumor of uncertain malignant potential."

Pleomorphic adenoma of the salivary glands with intravascular tumor deposits: a diagnostic pitfall

The diagnosis of pleomorphic adenoma (PA) of salivary glands is usually straightforward posing few diagnostic problems for the general surgical histopathologist. The purpose of our investigation was to present a series of 22 cases of PA of major salivary glands, each of which contained small foci of tumor within vascular spaces. This feature has previously been described very rarely in PA and may represent a significant diagnostic pitfall. The patients included 12 women and 10 men, ranging in age at diagnosis from 17 to 82 years. Histopathologically, all 22 tumors displayed the features of PA with mixed epithelial and myoepithelial growth patterns and chondromyxoid areas. None of these neoplasms showed any cytologic evidence of malignancy. In all cases, there were multiple dilated thin-walled and/or muscular thick-walled blood vessels containing small intraluminal collections of neoplastic cells with or without myxoid stromal components. The intravascular tumor cells expressed cytokeratins, and in some cases they were also immunoreactive for S-100 protein, GFAP, D2-40, and p63 protein. The intravascular location of the neoplastic cells was confirmed by CD31, CD34, and factor VIII-related antigen immunostains. Reaction for D2-40 was negative in the endothelium of the involved vessel in all cases, confirming that they were vascular rather than lymphatic channels. Seven patients (36%) underwent fine-needle aspiration biopsy 25 days to several years before excision of the tumor. Follow-up of the patients in our series revealed no cases of recurrence or metastasis (range, 6 mo to 9.5 y; mean 3.8 y; median 3.5 y). The biological significance of intravascular tumor in PA is not clear, but there is growing evidence that it is an innocuous phenomenon that might be related to artifactual spillage caused by tumor injury presumably by either fine-needle aspiration or intraoperative trauma.