Clinical and Histopathologic Study of Apocrine-Type Mixed Tumor of the Skin.

ABSTRACT: Mixed tumor of the skin (MTS) is a tumor characterized by folliculosebaceous-apocrine differentiation. Because of the wide range of histological variations, understanding the unique features of MTS can help improve diagnosis. This study describes the histopathological characteristics of MTS, mainly apocrine-type MTS (AMT), using 166 cases of AMT. We found that nodular aggregates of myoepithelial cells, mucinous changes in the stroma, and follicular differentiation were standard characteristic features of MTS. Among the cases studied, 67% showed prominent follicular germinative cells and 40% showed prominent lipomatous metaplasia in the stroma. These cases often pose difficulties for the diagnosis of AMT because of insufficient evidence of sweat glands or myoepithelial cell differentiation. This is the first study to examine how the histological features of AMT change as the tumor extends deeper into the dermis. We found that the proportion of AMT with folliculosebaceous differentiation and large lumina increased as it got deeper into the dermis. Histopathological diagnosis of MTS is vital because the clinical symptoms lack specificity. This study enhances our understanding of the histopathological characteristics of MTS.

A preliminary study investigating the detection of lymphovascular invasion in germ cell tumors of the testis with double staining for OCT4/CD34.

Lymphovascular invasion (LVI) is a relevant prognostic factor in germ cell tumors of the testis (GCTT) and it has been included in the AJCC staging system. Nevertheless, its histological assessment is challenging, with low/moderate interobserver agreement also among expert uropathologists. Few studies focused on the potential role of immunohistochemistry to solve this critical issue; as result, in current guidelines there is no indication for additional staining to detect this histological feature. In the present study, we investigated the detection of LVI invasion in a small cohort of GCTT with double staining for OCT4/CD34. Although our results need to be validated in larger case series with follow-up data, they suggest as OCT4/CD34 could be a useful tool for the histological assessment of these tumors, helping to identify some histological mimickers of LVI and modifying the pT/stage in a significant percentage of patients.

Gene expression microarray analysis of adult testicular germ cell tumor: a comparison between pure-type seminomas and seminoma components in mixed tumors.

We previously demonstrated a genetic evidence of the progression from seminoma to embryonal carcinoma in mixed testicular germ cell tumors (TGCTs). This process, the "reprogramming" of seminoma cells, is crucial for pathological tumorigenesis and should be kept in mind while designing clinical therapeutic strategies. We hypothesized that a comparison between pure-type seminomas and seminoma components in mixed tumors (mixed-type seminomas) could reveal early changes in the reprogramming process. In the present study, we performed gene expression microarray analysis of six pure-type and six mixed-type seminomas. Hierarchical clustering analysis properly grouped each type of seminomas into a separated cluster. Supervised analysis between pure-type and mixed-type seminomas revealed 154 significantly dysregulated genes (Storey-adjusted q < 0.05). The genes with the highest overexpression in mixed-type seminomas compared with the pure-type seminomas included MT1 isoforms, PRSS8, TSC22D1, and SLC39A4; downregulated genes included DEFB123, LMTK2, and MYRF. Functional annotation analysis of the differentially expressed genes revealed that the top-ranked functional categories were related to cellular zinc metabolism and consisted of MT1 isoforms and SLC39A4, the results of which were validated using quantitative polymerase chain reaction and immunohistochemical analysis. In conclusion, this research provides further evidence that pure and mixed types of seminomas are molecularly different, which may contribute to elucidate the reprogramming mechanism in the progression of TGCTs.

DNA mismatch repair deficiency and p53 abnormality are age-related events in mixed endometrial carcinoma with a clear cell component.

Mixed endometrial carcinoma (MEC) is defined as a tumor composed of two or more spatially distinct subtypes, at least one of which is serous or clear cell carcinoma. In this study, the clinicopathological features of 15 MEC cases containing a clear cell component (MEC-C) were investigated. The ages of patients ranged from 32 to 83 years (median, 61 years). The combinations of carcinoma components observed were endometrioid and clear cell in ten patients; endometrioid, clear cell and serous in three; and clear cell and serous in two. Immunohistochemically, nine had DNA mismatch repair (MMR) protein deficiency (MMR-d), nine had loss of ARID1A and three cases had aberrant p53 expression. MMR-d and loss of ARID1A showed a strong correlation. Only one case showed both MMR-d and aberrant p53 expression. The patients with MMR-d were younger than those without MMR-d (median; 58 years vs. 71 years). Loss of ARID1A also showed significant predilection for younger women than ARID1A intact cases. In conclusion, MMR-d was observed in 60 % of MEC-C, showed predilection for young women, and was associated with ARID1A loss. In contrast, non- MMR-d MEC-C occurred in elder women and some tumors may associate with TP53 mutation. These findings suggest that MEC-C develop via two different molecular mechanisms and they are age-related events.

Dermal and Intraepidermal Merkel Cell Carcinoma With Squamous Cell Carcinoma: A Report of a Rare Case With Special Reference to the Touch Dome.

ABSTRACT: In skin containing hair follicles, specialized epithelial structures known as "touch domes (TDs)" are located where the Merkel cells are clustered. We explored the histogenetic relationship between intraepidermal and dermal Merkel cell carcinomas (MCCs) and investigated which transformed progenitor cells can develop into intraepidermal MCC. We encountered an association between an extremely rare case of dermal and intraepidermal MCC with squamous cell carcinoma, which was examined using standard immunohistochemical methods with various epithelial, neuroendocrine, and TD markers including several immunohistochemical markers. Differential expression levels of CK20 and CD56 were found between intraepidermal and dermal MCCs, indicating molecularly distinct MCC populations. CK15 and CK17, expressed in TDs, were partially expressed in the intraepidermal neuroendocrine component at the tumor periphery in intraepidermal MCC with squamous cell carcinoma. These differences may suggest that the origin of dermal and intraepidermal MCCs is different under pathological conditions. We hypothesize that intraepidermal MCC is derived from tissue-specific stem cells localized within TDs.

Clear Cell Hidradenoma-Basal Cell Carcinoma Collision.

ABSTRACT: A 91-year-old man presented with a tumor on the left temporal area, clinically suspicious of basal cell carcinoma. The histopathologic study showed a central solid-cystic tumor composed by 3 different types of cells (clear or finely granular cells, polygonal cells, and squamoid cells). It had a sclerotic stroma. At the periphery, another tumor composed by smaller interconnected nests was evident. Some nests were separated from the stroma by clefts. The stroma of this second tumor was highly cellular. There was a sharp delimitation between both tumors, with no transitional area. Immunochemistry demonstrated they are different tumor. A diagnosis of clear cell hidradenoma-basal cell carcinoma collision was performed. To the best of our knowledge, this is the first description of this challenging association.

Coexisting well-differentiated and anaplastic thyroid carcinoma in the same primary resection specimen: immunophenotypic and genetic comparison of the two components in a consecutive series of 13 cases and a review of the literature.

Anaplastic carcinoma (AC) is a rare but highly aggressive form of thyroid cancer. It mostly arises on a background of pre-existing well-differentiated cancer (WDC); however, whether it evolves directly from a WDC or originates as a second independent neoplasm is still to be defined. To obtain further insights into these mechanisms, we performed morphological, immunohistochemical, and next-generation sequencing analyses to compare AC and its associated WDC in a subset of 13 surgically resected specimens. Histologically, most WDC were of aggressive subtypes. Papillary carcinomas (8 cases; 62%) were tall cell (4/8), columnar (1/8), classic with hobnail features (1/8), classic and follicular variant in the remaining 2 cases; Hürthle cell and follicular carcinomas were present in 5 (38%) and in 1 (8%) patient, respectively. One patient harbored both a PTC, follicular variant, and a Hürthle cell carcinoma. We did not find any correlation between a histotype of WDC and a specific anaplastic growth pattern. Immunohistochemically, ACs retained pankeratin/PAX8 expression but with significantly lower levels than WDCs, and they tended to lose TTF1 expression, as can be expected within a dedifferentiation process. In addition, AC showed a more frequent expression of p63 and/or SMA, a mutated pattern of p53, and an abnormal expression of p16. Genetic analysis showed that the number of mutations was higher in AC than in the associated WDC, confirming a role of the progressive accumulation of genetic damage in this transition. We observed that mutations found in the WDCs were consistently identified in the anaplastic counterparts, further supporting the hypothesis of a developmental link.

Mixed large cell neuroendocrine carcinoma and squamous cell carcinoma of the colon: detailed molecular characterisation of two cases indicates a distinct colorectal cancer entity.

We present two rare cases of mixed large cell neuroendocrine carcinoma and squamous cell carcinoma of the colon. A literature search revealed only three published cases with similar histology but none of these reports provided profound molecular and mutational analyses. Our two cases exhibited a distinct, colon-like immunophenotype with strong nuclear CDX2 and ß-catenin expression in more than 90% of the tumour cells of both components. We analysed the two carcinomas regarding microsatellite stability, RAS, BRAF and PD-L1 status. In addition, next-generation panel sequencing with Ion AmpliSeq™ Cancer Hotspot Panel v2 was performed. This approach revealed mutations in FBXW7, CTNNB1 and PIK3CA in the first case and FBXW7 and RB1 mutations in the second case. We looked for similar mutational patterns in three publicly available colorectal adenocarcinoma data sets, as well as in collections of colorectal mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs) and colorectal neuroendocrine carcinomas. This approach indicated that the FBXW7 point mutation, without being accompanied by classical adenoma-carcinoma sequence mutations, such as APC, KRAS and TP53, likely occurs at a relatively high frequency in mixed neuroendocrine and squamous cell carcinoma and therefore may be characteristic for this rare tumour type. FBXW7 codifies the substrate recognition element of an ubiquitin ligase, and inactivating FBXW7 mutations lead to an exceptional accumulation of its target ß-catenin which results in overactivation of the Wnt-signalling pathway. In line with previously described hypotheses of de-differentiation of colon cells by enhanced Wnt-signalling, our data indicate a crucial role for mutant FBXW7 in the unusual morphological switch that determines these rare neoplasms. Therefore, mixed large cell neuroendocrine and a squamous cell carcinoma can be considered as a distinct carcinoma entity in the colon, defined by morphology, immunophenotype and distinct molecular genetic alteration(s).

Collision Tumor Composed of an Inflammatory Myofibroblastic Tumor and Adenocarcinoma of the Colon: a Rare Entity.

This report presents the case of an 83-year old man with a collision tumor consisting of an inflammatory myofibroblastic tumor (IMT) and adenocarcinoma of the left colon. As the clinical and radiologic features of IMT are non-specific, only the accurate histopathological examination from the left hemicolectomy specimen was diagnostic. Although the prognosis of a colorectal IMT seemed more favorable than in other sites, four months after surgery the patient developed a tumor relapse. Therefore, malignant behavior of IMT could not be totally excluded. Recent studies have demonstrated that a chromosomal rearrangement involving 2p23, the site of the anaplastic lymphoma kinase (ALK) gene, is present in a subset of these tumors. In our patient, tumor cells did not present ALK-1 perinuclear positivity and it could have indicated a less favorable prognosis. The collision of these different entities is extremely rare and this is the first case reported in literature. Further cases of collision tumors with clinical information including their treatment and prognosis are needed.

Molecular Profiles of Mixed Endometrial Carcinoma.

Mixed endometrial carcinomas are defined as a combination of 2 or more distinct histologic subtypes, one of which must be a type II tumor comprising at least 5% of the tumor volume. The oncogenesis of these tumors remains unclear, particularly in light of the increasingly appreciated morphologic overlap among subtypes, as well as evolving molecular data. We evaluated 8 cases of mixed endometrial carcinoma, including 4 endometrioid (EC)/serous (SC), 1 SC/clear cell (CC), and 3 EC/CC cases, to study the underlying molecular features and oncogenic mechanisms at play. Each component was analyzed by a targeted next-generation sequencing assay. All tumors shared mutations in both components. In 6 cases, one component showed additional mutations. Two EC/SC cases showed shared mutations and mutations unique to each component. When present, unique mutations were typically seen in the SC component, including variants in POLE and TP53, as well as potentially targetable genes DDR2, MAP2K1, and CCNE1. In EC/SC tumors, ERBB2 abnormalities were seen in 2 cases. EC/CC cases showed FGFR2 activating mutations in the EC component only. No fusion drivers were identified. Our data suggest that the majority of these tumors begin as a single clone and diverge along 2 pathways: (1) tumor progression, with one component showing additional mutations, and (2) tumor divergence, in which tumor components have both shared mutations and mutations unique to each component. In addition, the findings suggest a component of morphologic mimicry in these tumors. Our findings are clinically relevant since targetable mutations may be present in only one component of mixed tumors.

Updates in the diagnosis of combined hepatocellular-cholangiocarcinoma.

Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare primary liver carcinoma showing variable degrees of differentiation toward hepatocellular and cholangiocellular carcinoma. Its great heterogeneity in term of morphology, immunophenotype, molecular, radiological and clinical features represents a challenge still to overcome. The multidisciplinary 2018 International Consensus on the nomenclature of cHCC-CCA allowed to define key issues of this entity. Here we review the historical controversies of cHCC-CCA, resume the key elements of the 2018 consensus, now incorporated in the 2019 WHO classification, and propose a short survival guide to help surgical pathologists facing cHCC-CCA in their routine workup.

Pancreatic Neoplasms With Acinar Differentiation: A Review of Pathologic and Molecular Features.

CONTEXT.­: Pancreatic acinar lesions encompass a broad spectrum of malignant tumors and benign reactive processes affecting both adults and children, with clinical, pathologic, and molecular features that are distinct from more common ductal neoplasms. Accurate morphologic diagnosis and molecular assessment of these uncommon neoplasms is critical for effective patient care. OBJECTIVE.­: To review the clinical, pathologic, and molecular features of pancreatic neoplasms with acinar differentiation, the most common of which is acinar cell carcinoma but which also includes mixed carcinomas with acinar components, cystic acinar lesions, and pancreatoblastoma. DATA SOURCES.­: We assessed the current primary literature, as well as recently updated diagnostic manuals. CONCLUSIONS.­: Pancreatic acinar neoplasms are a morphologically and molecularly heterogeneous group of diseases that are characterized by acinar differentiation of at least a subset of the neoplastic cells, defined either morphologically (granular cytoplasm, single prominent nucleoli) or immunohistochemically. Squamoid nests are a key morphologic feature of pancreatoblastoma. Alterations in WNT signaling and chromosomal 11p loss are common molecular features of both acinar cell carcinoma and pancreatoblastoma. Targetable molecular alterations in acinar carcinoma include BRAF rearrangements and DNA repair defects, including mismatch repair deficiency and BRCA pathway defects. For practicing pathologists, morphologic recognition of such acinar neoplasms is critical, and in the future, molecular diagnostics to identify lesions susceptible to targeted therapy will likely form an important component of patient care.

Gastrointestinal mixed adenoneuroendocrine carcinoma (MANEC): An immunohistochemistry study of 13 microsatellite stable cases.

BACKGROUND: Mixed adenoneuroendocrine carcinoma (MANEC) is currently included in the category of neuroendocrine carcinomas but the therapeutically management is not yet defined. AIMS: To present the immunohistochemical (IHC) features of the epithelial mesenchymal transition (EMT) of MANEC. MATERIALS AND METHODS: The clinicopathological features of 13 consecutive cases of MANEC (6 gastric and 7 colorectal) were correlated with the IHC expression of the biomarkers E-cadherin, ß-catenin, N-cadherin, vimentin, maspin, CD44 and S100. In all of the cases open surgery was performed. RESULTS: All of the cases showed microsatellite stable status, expressed E-cadherin and membrane ß-catenin in both components (neuroendocrine and adenocarcinoma) and were negative for N-cadherin, vimentin and S-100. The colorectal MANECs were negative for maspin. In gastric MANECs, maspin showed cytoplasm positivity in the neuroendocrine component and nuclear translocation in the adenocarcinoma cells. CD44 was positive in all of the cases, in both components. No tumor buddings were identified. Three of the 13 patients survived for at least 32 months, all of them showing lymphatic emboli but not lymph node metastases. Pure neuroendocrine lymph node metastases were seen in only four of the cases: one from stomach, two of the ascending colon and two cases of the upper rectum. CONCLUSIONS: Gastrointestinal MANEC is a microsatellite stable tumor with nodular growth, which components might originate from a CD44-positive stem-like precursor cell. Lymph node status remains the most reliable prognostic parameter and agressivity seems to not be influenced by tumor budding degree or EMT-related features. The histologic aspect of metastatic component (neuroendocrine versus adenocarcinoma) should be included in the histopathological reports and might be used for establishing the proper-targeted therapy of MANEC.

An Atypical Fibroxanthoma and Intradermal Nevus Collision Tumor-Potential for Misdiagnosis.

Atypical fibroxanthomas (AFX) are rare cutaneous tumors, which typically present as a solitary ulcerated papule or nodule on sun-damaged skin. Despite malignant-appearing features on histology, AFX typically pursue a benign clinical course. In rare instances, AFX can form collision tumors with other lesions. However, to the best of our knowledge, AFX in collision with a nevus has never been previously reported. In this study, we describe such a lesion for its novelty and challenge in diagnosis, as this case was originally considered to be melanoma arising in a nevus. On histologic examination, there were 2 distinct populations of cells; one composed of markedly atypical and pleomorphic epithelioid and oval to spindled cells, consistent with AFX, and the other, a bland-appearing intradermal nevus with congenital features. The AFX population stained positive with smooth muscle actin, CD10, and CD68 and was negative for S100, SOX10, Melan-A, desmin, pancytokeratin, CK5/6, and p63. Deep to this was a second population of small, bland-appearing melanocytes in a broad, band-like distribution. This unusual collision tumor between AFX and an intradermal nevus highlights the important role immunohistochemistry plays in avoiding the misdiagnosis and potential overtreatment of benign or low-grade lesions, and in identifying potential mimickers.

Sarcomatoid carcinomas of the gallbladder: clinicopathologic characteristics.

Sarcomatoid carcinomas recently came into the spotlight through genetic profiling studies and also as a distinct model of epithelial-mesenchymal transition. The literature on sarcomatoid carcinomas of gallbladder is limited. In this study, 656 gallbladder carcinomas (GBC) were reviewed. Eleven (1.7%) with a sarcomatoid component were identified and analyzed in comparison with ordinary GBC (O-GBC). Patients included 9 females and 2 males (F/M = 4.5 vs. 3.9) with a mean age-at-diagnosis of 71 (vs. 64). The median tumor size was 4.6 cm (vs. 2.5; P = 0.01). Nine patients (84%) presented with advanced stage (pT3/4) tumor (vs. 48%). An adenocarcinoma component constituting 1-75% of the tumor was present in nine, and eight had surface dysplasia/CIS; either in situ or invasive carcinoma was present in all cases. An intracholecystic papillary-tubular neoplasm was identified in one. Seven showed pleomorphic-sarcomatoid pattern, and four showed subtle/bland elongated spindle cells. Three had an angiosarcomatoid pattern. Two had heterologous elements. One showed few osteoclast-like giant cells, only adjacent to osteoid. Immunohistochemically, vimentin, was positive in six of six; P53 expression was > 60% in six of six, keratins in six of seven, and p63 in two of six. Actin, desmin, and S100 were negative. The median Ki67 index was 40%. In the follow-up, one died peri-operatively, eight died of disease within 3 to 8 months (vs. 26 months median survival for O-GBC), and two were alive at 9 and 15 months. The behavior overall was worse than ordinary adenocarcinomas in general but was not different when grade and stage were matched. In summary, sarcomatoid component is identified in < 2% of GBC. Unlike sarcomatoid carcinomas in the remainder of pancreatobiliary tract, these are seldom of the "osteoclastic" type and patients present with large/advanced stage tumors. Limited data suggests that these tumors are aggressive with rapid mortality unlike pancreatic osteoclastic ones which often have indolent behavior.

Genomic and Transcriptomic Profiling of Combined Hepatocellular and Intrahepatic Cholangiocarcinoma Reveals Distinct Molecular Subtypes.

We performed genomic and transcriptomic sequencing of 133 combined hepatocellular and intrahepatic cholangiocarcinoma (cHCC-ICC) cases, including separate, combined, and mixed subtypes. Integrative comparison of cHCC-ICC with hepatocellular carcinoma and intrahepatic cholangiocarcinoma revealed that combined and mixed type cHCC-ICCs are distinct subtypes with different clinical and molecular features. Integrating laser microdissection, cancer cell fraction analysis, and single nucleus sequencing, we revealed both mono- and multiclonal origins in the separate type cHCC-ICCs, whereas combined and mixed type cHCC-ICCs were all monoclonal origin. Notably, cHCC-ICCs showed significantly higher expression of Nestin, suggesting Nestin may serve as a biomarker for diagnosing cHCC-ICC. Our results provide important biological and clinical insights into cHCC-ICC.

Goblet Cell Carcinoid/Carcinoma: An Update.

Goblet cell carcinoid (GCC) or goblet cell carcinoma is a unique mixed endocrine-exocrine neoplasm that is almost exclusively seen in the appendix. The hallmark of GCC is the concentric infiltration of the appendiceal wall by small tight clusters, nests or cords of tumor cells that exhibit a goblet cell morphology with a small compressed nucleus and conspicuous intracytoplasmic mucin. The coexistence of high-grade adenocarcinoma with GCC has been increasingly recognized as a common finding, which has been called adenocarcinoma ex GCC or mixed GCC-adenocarcinoma. A number of studies have shown that it is the high-grade adenocarcinomatous component that dictates the prognosis. Several histologic classification/grading systems have been proposed, which correlate with overall patient survival. Treatment options are primarily based on tumor stage and the presence or absence of a high-grade adenocarcinomatous component.

Phenotypic and molecular dissection of metaplastic breast cancer and the prognostic implications.

Metaplastic breast carcinoma (MBC) is relatively rare but accounts for a significant proportion of global breast cancer mortality. This group is extremely heterogeneous and by definition exhibits metaplastic change to squamous and/or mesenchymal elements, including spindle, squamous, chondroid, osseous, and rhabdomyoid features. Clinically, patients are more likely to present with large primary tumours (higher stage), distant metastases, and overall, have shorter 5-year survival compared to invasive carcinomas of no special type. The current World Health Organisation (WHO) diagnostic classification for this cancer type is based purely on morphology - the biological basis and clinical relevance of its seven sub-categories are currently unclear. By establishing the Asia-Pacific MBC (AP-MBC) Consortium, we amassed a large series of MBCs (n = 347) and analysed the mutation profile of a subset, expression of 14 breast cancer biomarkers, and clinicopathological correlates, contextualising our findings within the WHO guidelines. The most significant indicators of poor prognosis were large tumour size (T3; p = 0.004), loss of cytokeratin expression (lack of staining with pan-cytokeratin AE1/3 antibody; p = 0.007), EGFR overexpression (p = 0.01), and for 'mixed' MBC, the presence of more than three distinct morphological entities (p = 0.007). Conversely, fewer morphological components and EGFR negativity were favourable indicators. Exome sequencing of 30 cases confirmed enrichment of TP53 and PTEN mutations, and intriguingly, concurrent mutations of TP53, PTEN, and PIK3CA. Mutations in neurofibromatosis-1 (NF1) were also overrepresented [16.7% MBCs compared to ∼5% of breast cancers overall; enrichment p = 0.028; mutation significance p = 0.006 (OncodriveFM)], consistent with published case reports implicating germline NF1 mutations in MBC risk. Taken together, we propose a practically minor but clinically significant modification to the guidelines: all WHO_1 mixed-type tumours should have the number of morphologies present recorded, as a mechanism for refining prognosis, and that EGFR and pan-cytokeratin expression are important prognostic markers. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mixed Adenoma Well-differentiated Neuroendocrine Tumor (MANET) of the Digestive System: An Indolent Subtype of Mixed Neuroendocrine-NonNeuroendocrine Neoplasm (MiNEN).

Mixed neuroendocrine-nonneuroendocrine neoplasm (MiNEN) consisting of adenoma and well-differentiated neuroendocrine tumor (NET) has been recently defined as "MANET." However, the clinico-pathologic and pathogenetic features of this entity are not thoroughly studied. We examined the clinico-pathologic features of 12 MANETs by expanding their p53 and ß-catenin expression profiles as well as the presence of microsatellite instability and KRAS, BRAF, and PIK3CA mutations in the 2 tumor components. In all cases, the adenomatous component represented the larger part of the lesions and the NET was localized in the deep central portion of polyps. In 9 cases the latter was represented by NET G1, in 2 by NET G2, and in 1 by NET G3. In all cases, the glandular and NET components were intimately admixed, with zone of transition between the tumor components. The NET component was p53 negative in all cases and 3 of 8 cases showed variable nuclear positivity for ß-catenin. All patients with follow-up data were alive and free of disease after a mean follow-up time of 9 years. No mutations in KRAS, BRAF, and PIK3CA genes and no microsatellite instability were found in both tumor components. Review of the literature also identified 59 previously reported MANETs and no tumor-related death has been found. Like mixed adenoneuroendocrine carcinomas, a high-grade malignant form of MiNENs with a poorly differentiated neuroendocrine carcinoma component, a common origin for both tumor constituents may be hypothesized. Moreover, the current series provides evidence that MANET is an indolent disease that needs to be distinguished from aggressive high-grade MiNENs.

The role of next-generation sequencing in the differential diagnosis of composite neoplasms.

Composite neoplasms (CNs) are rare and diagnostically challenging lesions that require differentiating between mixed clonal tumors with divergent phenotypes (MT), collision of 2 independent tumors adjacent to each other (CT), and tumor-to-tumor metastasis (TTM). To that end, pathologists have traditionally used immunohistochemistry and limited molecular studies, such as Sanger sequencing. Herein we evaluate the potential application of NGS in the differential diagnosis of these rare neoplasms. Four CNs were included in the study. Two were diagnosed as MT (mixed adenoneuroendocrine carcinoma of the gallbladder and metastatic papillary thyroid carcinoma with squamous dedifferentiation) and 2 were interpreted as TTM (esophageal adenocarcinoma to lung adenocarcinoma and small cell carcinoma of the lung to meningeal melanoma). Diagnoses were made using clinical, histologic, and immunophenotypic information, with the aid of limited molecular studies in 2 cases. Formalin-fixed, paraffin-embedded tissue was dissected for DNA and RNA extraction, and NGS was performed using the Oncomine Comprehensive Panel. The 2 tumors initially interpreted as MT showed shared genetic aberrations in the different neoplastic components, supporting the pathologic diagnosis. NGS results for the lesion diagnosed as esophageal adenocarcinoma metastatic to lung adenocarcinoma did not support the histopathologic interpretation and were deemed inconclusive. However, the identification of an identical CDKN2A mutation in all components and in the adjacent benign lung parenchyma suggests a possible germline aberration. Sequencing results in the last case were clearly supportive of TTM. This study illustrates the role of NGS in the diagnostic workup of CNs, as an adjunct to light microscopy and immunohistochemistry.