Hemangioblastoma-like clear cell stromal tumor of the lung

"Putting the cart before the horse": an update on promiscuous gene fusions in soft tissue tumors

The ever-increasing availability and affordability of molecular genetic testing has revolutionized our understanding of the pathogenesis and proper classification of soft tissue tumors but has also brought new challenges. As is known, many soft tissue tumors harbor gene fusion events, and while it was initially thought that individual entities would be defined by single, specific fusions, it quickly became clear that some entities could be caused by several different fusion events (e.g., EWSR1::FLI1, EWSR1::ERG, EWSR1:FEV and others in Ewing sarcoma). More recently, it has become apparent that these fusion events themselves are "promiscuous", appearing in more than one discrete entity (e.g., EWSR1::CREB1 in clear cell sarcoma, angiomatoid fibrous histiocytoma and others). This review article will briefly discuss the best known examples of genetic promiscuity, the EWSR1/FUS::ATF1/CREB1 and ETV6::NTRK3 fusions, and more comprehensively cover recently discovered and less well-known examples of genetic promiscuity, including EWSR1::WT1, MALAT1::GLI1, YAP1::TFE3 and fusions involving members of the FET and ETS gene families.

Uncommon Tumors of the Lung: Recently Described and Rediscovered Tumors

CONTEXT.—

The great majority of primary pulmonary neoplasms are represented by non-small cell carcinomas-adenocarcinoma and squamous cell carcinoma. In addition, there is another group of neoplasms such as those of neuroendocrine origin that also represent a meaningful subset of primary lung neoplasms. Basically, any other tumor that is not in these groups of tumors may represent an unusual lung neoplasm.

OBJECTIVE.—

To highlight more recently described unusual tumoral entities that may represent a challenge in diagnosis and that require awareness of their existence.

DATA SOURCES.—

This is a review of 3 different entities: bronchiolar adenoma, adenofibroma, and hemangioblastoma-like clear cell stromal tumor. These tumoral conditions are rare, and a review of the literature is presented. The most relevant morphologic, immunohistochemical, and molecular aspects of bronchiolar adenoma, adenofibroma, and hemangioblastoma-like clear cell stromal tumor are presented. The difficulty of arriving at an unequivocal diagnosis in small biopsies is highlighted.

CONCLUSIONS.—

The 3 entities represent uncommon tumors occurring primarily in the lung and a diagnostic challenge not only in biopsy specimens but also often in surgically resected specimens. The use of immunohistochemical stains and in some cases of molecular diagnostics is of aid in arriving at final interpretation.

Perivascular Epithelioid Cell Tumor of the Lung With a Novel YAP1::TFE3 Fusion

Perivascular epithelioid cell tumor (PEComa) belongs to a family of rare mesenchymal neoplasms that share characteristic morphologic, immunohistochemical and molecular findings. In this report, we provide a detailed clinicopathological characterization of a PEComa incidentally discovered in the right lung of a 53-year-old woman. This tumor with epithelioid cell morphology and myomelanocytic differentiation demonstrated a TFE3::YAP1 fusion by targeted RNA sequencing. While a subset of PEComas shows TFE3 rearrangements, fusion with YAP1 has not been systematically documented in this entity. Clear cell stromal tumor of the lung and epithelioid hemangioendothelioma characteristically display the TFE3::YAP1 fusion; however, as currently defined, both lack myomelanocytic features. Here, we describe a novel TFE3 fusion partner that further expands the spectrum of molecular alterations seen in PEComa.

Emerging fusion-associated mesenchymal tumours: a tabular guide and appraisal of five 'novel' entities

AIMS

The field of molecular pathology has undergone significant advancements in the clinical impact of sarcoma diagnosis, resulting in challenges to nosology of bone and soft tissue tumours. The surge in molecular data has led to the identification of novel fusions and description of new 'entities'. To illustrate this, we have selected five emerging entities with novel fusions: clear cell stromal tumour of the lung with YAP1::TFE3 fusion, GAB1::ABL1 fusion spindle cell neoplasm, NUTM1-rearranged sarcomas, NR1D1-rearranged sarcomas and calcified chondroid mesenchymal neoplasms.

METHODS

Literature for the relevant case reports and case series of these five entities were reviewed and clinicopathological data was collected. Additionally, this review includes a table format of recently described fusion-associated mesenchymal neoplasms.

RESULTS

The morphological and immunohistochemical features, along with diagnostic challenges, are discussed for each entity.

CONCLUSIONS

Here, we have provided a review of selected emerging mesenchymal neoplasms, which of these neoplasms will meet the threshold to be 'new entities' remains to be determined.

Inflammatory spindle cell PEComa of the lung with YAP1::TFE3 fusion: a report of two cases and a potential relationship with clear cell stromal tumour

AIMS

The PEComa family of tumours is defined by spindle/epithelioid cells with myomelanocytic differentiation. A small subset harbours TFE3 fusion; however, YAP1::TEE3 has not been reported. Clear cell stromal tumour of the lung (CCST-L) is an emerging entity characterized by spindle to epithelioid cells with focal cytoplasmic clearing, inflammatory infiltrates, no myomelanocytic differentiation, and YAP1::TFE3 fusion. Herein, we report two cases of lung tumours with myomelanocytic differentiation that showed inflammatory spindle cell histology, focal epithelioid clear cells, as well as YAP1::TFE3 fusion.

METHODS AND RESULTS

The patients were both men, aged 61 and 68 years. The tumours in both cases presented as well-circumscribed solid masses involving the lung hilum. After lobectomy, no recurrence was observed at 7 and 32 months. Both tumours shared storiform to short fascicular growth of long spindle cells, with a minor component of epithelioid cells showing clear cytoplasm in the background of substantial intratumoral chronic inflammation and dilated blood vessels. One tumour showed focal melanin deposition. Both tumours were immunohistochemically positive for HMB45, Melan A, and h-caldesmon. Fluorescence in situ hybridization assays indicated the presence of YAP1::TFE3 fusions, which was confirmed by RNA sequencing in one case tested, and by immunohistochemical TFE3 expression and loss of YAP1 C-terminus staining.

CONCLUSION

We present two cases of inflammatory spindle to epithelioid cell tumours of the lungs with myomelanocytic differentiation and YAP1::TFE3 fusion. This unique morphology and gene fusion suggest that these tumours may constitute a distinct subset of lung PEComa. Furthermore, morphological and molecular overlap with CCST-L gives rise to a hypothesis of a potential inherent relationship between PEComa and CCST-L.

Clear Cell Stromal Tumor of the Lung: Clinicopathologic, Immunohistochemical, and Molecular Characterization of Eight Cases

Clear cell stromal tumor is a recently described mesenchymal neoplasm of the lung, characterized by spindle cells with variably clear-to-pale eosinophilic cytoplasm and prominent vascularity, as well as a recurrent YAP1::TFE3 gene fusion in most cases. Diagnosis can be challenging given its rarity and the lack of supportive immunohistochemical (IHC) markers aside from TFE3. To date, less than 20 cases have been reported, and data on clinical behavior are also limited. Although most appear to be benign, aggressive behavior has been reported rarely. In this study, we present the largest multiinstitutional series of clear cell stromal tumor to date, comprising a total of 8 cases and including 6 previously unpublished cases. We investigate its clinicopathologic and genomic features, while also assessing the diagnostic use of IHC for YAP1 C-terminus. Five patients were men and 3 were women. The median age was 59 years (range: 35-84 years). In all cases, a TFE3 rearrangement was demonstrated by either fluorescence in situ hybridization or DNA/RNA sequencing. In 7 tumors, the YAP1::TFE3 fusion was identified by sequencing. We demonstrate that the combination of YAP1 C-terminus loss and TFE3 overexpression using IHC reliably predicts an underlying YAP1::TFE3 fusion in these neoplasms and may be more sensitive than TFE3 fluorescence in situ hybridization. Although the median follow-up time for our study was short (18 months, available in 7 cases), all cases pursued a benign clinical course, with no recurrences or metastases. Our study provides further characterization of this novel entity, supporting its wider recognition.

Clear cell stromal tumor of the lung: Report of 3 cases with emphasis on multifocal tumors

We describe 3 patients with clear cell stromal tumor (CCST) of the lung, all of whom presented with multifocal disease. The patients were 2 men and 1 woman aged 47-58 years (mean, 54 years). Two patients had evidence of autoimmune disease and their pulmonary disease was an incidental finding; one patient presented with non-specific respiratory symptoms. Radiologic imaging revealed multiple pulmonary nodules in all patients. Histologically, the tumors were solid-cystic and composed of cytologically bland, medium-sized ovoid to spindle cells with eosinophilic to clear cytoplasm arranged in a subtle nested pattern. These tumor cells were set in a highly vascularized stroma. Occasional cytologic atypia with multinucleated tumor cells was noted but mitotic activity was low. An infiltrate of mixed inflammatory cells was apparent in all tumors. Immunohistochemical analysis demonstrated diffuse expression of vimentin and TFE3 in all cases. Next generation sequencing revealed the presence of YAP1::TFE3 fusion in 1/1 case. All patients have remained alive albeit with stable or progressive disease, 24-66 months after diagnosis. These cases highlight the existence of multifocal pulmonary CCST and seem to support the notion that multifocality in CCST may be associated with more protracted clinical course. Awareness of the existence of multifocal pattern is important for patient management and prognosis.

Non-small cell lung carcinoma with clear cell features: a clinicopathologic, immunohistochemical, and molecular study of 31 cases

Non-small cell lung carcinoma with predominantly clear cell features is a rare histologic presentation of lung carcinoma. We have examined 31 cases of lung carcinomas showing extensive clear cell features. The patients were 10 women and 21 men aged 47-92 years (mean: 70 years). The tumors showed a predilection for the right upper and lower lobes and measured from 0.8 to 9.5 cm (mean: 4.2 cm). By immunohistochemistry, 9 cases were typed as adenocarcinoma, 19 cases as squamous cell carcinoma, and 3 showed a "null" phenotype with complete loss of markers for adenocarcinoma or squamous cell carcinoma. Most cases that typed as adenocarcinoma showed a solid growth pattern. A subset of the solid adenocarcinoma cases showed a distinctive "pseudosquamous" morphology. Next-generation sequencing was performed in 20 cases and showed a variety of molecular alterations. The most common abnormalities were found in the TP53 gene (9 cases), FGFR gene family (8 cases), KRAS (5 cases), AKT1 (5 cases), and BRAF (3 cases). Clinical follow-up was available in 21 patients; 16/21 patients died of their tumors from 6 months to 12 years after initial diagnosis (mean: 4.2 years, median: 1.5 years). Four patients were alive and well from 4 to 27 years (mean: 11.5 years, median: 7.5 years); all were pathologic stage 1 or 2. NSCLC with clear cell features can display aggressive behavior and needs to be distinguished from various other tumors of the lung that can show clear cell morphology. The identification of targetable molecular alterations in some of these tumors may be of value for therapeutic management.

Clear cell stromal tumor of the lung with multinucleated giant cells: a report of a case with YAP1-TFE3 fusion

BACKGROUND

Clear cell (hemangioblastoma-like) stromal tumor of the lung (CCSTL) is a rare pulmonary neoplasm. Recently, 9 cases of CCSTL harboring the YAP1-TFE3 gene fusion have been described, and it has been suggested that this aberration could be a characteristic feature of this tumor.

CASE PRESENTATION

We here report another case of CCSTL in a 57-year-old male, which presented as a solitary lung nodule 45 mm in the greatest dimension. Microscopically, the tumor consisted of epithelioid to spindled cells with mild-to-moderate nuclear atypia, finely granular or vesicular chromatin, and small nucleoli. Nuclear indentations were a common finding. There were up to 3 mitoses per 10 HPF. The cytoplasm was slightly eosinophilic or clear. Scattered non-tumor large multinucleated cells were present. Immunohistochemically, the tumor cells showed diffuse positivity for TFE3, CD10, vimentin, and IFITM1. Other markers examined were negative, and the expression of lineage-specific markers was not found. NGS analysis revealed a fusion transcript of the YAP1 and TFE3 genes, and a pathogenic variant of the MUTYH gene.

CONCLUSION

Our finding supports the recent data suggesting that CCSTL represents a distinct entity characterized by the recurrent YAP1-TFE3 fusion.

Clear cell stromal tumor of the lung with YAP1::TFE3 fusion: four cases including case with highly aggressive clinical course

Clear cell stromal tumor of the lung (CCST-L) is a rare, recently recognized neoplasm, which has been found to express TFE3 and harbor YAP1::TFE3 fusions. Initial data suggested a benign process, however a single reported case gave rise to distant metastases. We sought to describe the clinicopathologic and molecular features of additional cases of CCST-L. Pathology and molecular archives were searched for cases of CCST-L or tumors with YAP1::TFE3 fusions. Clinical features were noted. Available slides, including immunohistochemical studies, were re-reviewed for diagnosis confirmation and assessment of pathologic features. Results of molecular studies were also recorded. Four tumors were identified, all occurring in women [median age 61 years (range: 24-69)]. Median tumor size was 4.4 cm (range: 1-9.5 cm); three tumors were unifocal and one was multifocal. Tumors were composed of epithelioid to spindled cells with eosinophilic to clear cytoplasm and grew in sheets, vague nests and short fascicles. Nuclear atypia was predominately mild, however two cases showed scattered atypical cells. Mitotic activity was generally low, though one case showed a mitotic count of 6/2 mm² . All tumors expressed TFE3 and harbored YAP1::TFE3 fusions. One case was unresectable and was treated with chemotherapy, and two underwent complete resection. One patient died of disease 7 months following diagnosis, while a second patient is alive with no evidence of disease after 43 months. Follow-up was not available for two cases. CCST-L expresses TFE3, harbors YAP1::TFE3 fusions and at least rare cases behave in an aggressive manner.

Case Report: Hemangioblastoma- Like Clear Cell Stromal Tumor of the Left Lower Lung

Background

Hemangioblastoma-like clear cell stromal tumor (HLCCST) is a recently reported neoplasm of the lung. Only 13 cases have been reported in four recent studies. Because HLCCST is very rare, it has not been included in the 2021 WHO classification of lung tumors.

Case Presentation

We report a case of HLCCST of the left lower lung in a 40-year-old female who was admitted to our hospital after pulmonary nodules were discovered. A plain chest CT scan showed a nodular high-density shadow measuring approximately 8 mm in diameter in the left lower lung. The lesion had clear borders, uneven internal density, and a low-density central vacuolar area. The left lower lung was partially resected by video-assisted thoracic surgery. Post-operative histopathologic diagnosis “hemangioblastoma-like clear cell stromal tumor” of the left lower lung.

Conclusion

The HLCCST is an extremely rare tumor and needs long-term follow-up after operation. Clinically, it may be easily confused with other benign and malignant tumors of the lung, and diagnosis is solely determined by histopathologic examination. This case suggests that immunohistochemical CD34 can be a strong positive marker.

Recurrent YAP1-TFE3 Gene Fusions in Clear Cell Stromal Tumor of the Lung

Clear cell (hemangioblastoma-like) stromal tumor of the lung (CCST-L) is a recently described distinctive rare pulmonary neoplasm of unknown histogenesis and molecular pathogenesis. Only 7 cases have been reported in 2 recent studies, although additional cases might have been reported under the heading of extraneural pulmonary hemangioblastoma. We herein describe 4 CCST-L cases, 3 of them harboring a YAP1-TFE3 fusion. The fusion-positive tumors occurred in 3 women, aged 29, 56, and 69 years. All presented with solitary lung nodules measuring 2.3 to 9.5 cm. Histologically, all tumors showed similar features being composed of relatively uniform medium-sized epithelioid to ovoid cells with clear cytoplasm and small round monomorphic nuclei. Scattered larger cells with enlarged hyperchromatic nuclei and marked pleomorphism were noted in 2 cases. The tumors were associated with a hypervascularized stroma with variable but essentially subtle resemblance to capillary hemangioblastoma and perivascular epithelioid cell tumor (PEComa). Immunohistochemistry was negative for all lineage-specific markers. Targeted RNA sequencing showed a YAP1-TFE3 fusion in 3 of 4 cases. All 3 tumors showed homogeneous nuclear TFE3 immunoreactivity. Two patients were disease free at 36 and 12 months. The third patient had biopsy-proven synchronous renal and hepatic metastases, but extended follow-up is not available (recent case). The fourth case lacking the fusion affected a 66-year-old woman and showed subtle histologic differences from the fusion-positive cases, but had comparable TFE3 immunoreactivity. CCST-L represents a distinctive entity unrelated to hemangioblastoma and likely driven by recurrent YAP1-TFE3 fusions in most cases. The relationship of our cases to the recently reported "hemangioblastoma-like" CCST-L remains to be determined. Analysis of larger series is paramount to delineate the morphologic spectrum and biological behavior of this poorly characterized entity.

YAP1-TFE3 gene fusion variant in clear cell stromal tumour of lung: report of two cases in support of a distinct entity

AIMS

Clear cell (haemangioblastoma-like) stromal tumour of the lung is a newly described, rare pulmonary neoplasm. Recurrent YAP1-TFE3 gene fusions have recently been reported in three cases. We describe two additional cases and confirm the characteristic YAP1-TFE3 gene fusion.

METHODS AND RESULTS

Two mesenchymal tumours of lung were identified from our soft tissue pathology consultation services and RNA sequencing was performed. Both cases were in male patients, aged 35 and 77 years. Both presented as solitary lung nodules measuring 3.9 and 7.5 cm in greatest dimension. Histopathologically, the tumours were composed of epithelioid to plump spindle cells arranged in packets and solid sheets. The cells showed fusiform to ovoid nuclei with open chromatin, variably prominent nucleoli and scant to moderate, clear to eosinophilic cytoplasm. Cytological atypia and significant mitotic activity were minimal. None of the tumours expressed lineage-specific immunophenotypical markers. Both cases were diffusely positive for nuclear TFE3. Unlike YAP1-TFE3-fused epithelioid haemangioendothelioma, for which the fusion breakpoint occurs in YAP1 exon 1 and TFE3 exons 4 or 6, the fusion breakpoints of these tumours were located in YAP1 exon 4 and TFE3 exon 7. Following complete surgical resection, neither of the tumours has recurred or metastasised (follow-up period 6-7 months).

CONCLUSIONS

We validate the presence of YAP1-TFE3 gene fusion in a unique primary mesenchymal tumour of lung, adding additional support for clear cell stromal tumour of the lung as a distinct entity.

Hemangioblastoma-like Clear Cell Stromal Tumor of the Lung: A Clinicopathologic and Immunohistochemical Study of 5 Cases

Five cases of an unusual primary benign stromal tumor designated as hemangioblastoma-like clear cell stromal tumor of the lung are presented. The patients are 4 women and 1 man between the ages of 39 and 52 years of age (average: 45.5 y). The patients presented with nonspecific symptoms of cough, chest pain, or dyspnea. None of the patients had any prior history of malignancy or tumor elsewhere. Diagnostic imaging showed the presence of an intrapulmonary tumor. Lobectomy was performed in all 5 patients. Grossly, the tumors were well-demarcated but not encapsulated with focal areas of hemorrhage without necrosis. Histologically, low power examination showed a cellular proliferation alternating with discrete dilated vessels reminiscent of a vascular neoplasm. Higher magnification showed medium-sized cells with clear cytoplasm arranged in sheets and cords. Mitotic activity and marked cellular atypia were not present. A wide panel of immunohistochemical studies was performed including epithelial, neural, muscle, vascular, and neuroendocrine markers, all of which showed negative staining. Tumor cells showed positive staining for vimentin. In 2 cases, fluorescence in situ hybridization for the solitary fibrous tumor was performed and was negative. Clinical follow-up in 3 patients showed no evidence of recurrence. The cases herein presented highlight an unusual benign stromal tumor of the lung, which needs to be considered in the differential diagnosis of tumors with a clear cell and vascular appearance.

EWSR1-CREM fusion in pulmonary mesenchymal neoplasm showing distinctive clear cell morphology

EWSR1-CREM gene fusions were recently discovered in several mesenchymal and epithelial tumors, including myxoid mesenchymal tumors of the central nervous system, rare cases of soft tissue clear cell sarcoma and angiomatoid fibrous histiocytoma, and hyalinizing clear cell carcinoma, which implicates the potential phenotypic diversities of tumors harboring an EWSR1-CREM fusion. We herein present an exceedingly indolent pulmonary mesenchymal tumor showing distinctive clinicopathological features. This tumor histologically displayed a small nest and alveolar pattern consisting of monomorphic clear cells intermingled with dilated anastomosing vasculature. Immunophenotypically, tumor cells were positive for vimentin and focally positive for synaptophysin, but negative for many immunohistochemical panels including keratins, EMA, desmin, mesothelial markers, melanotic markers, smooth muscle actin, inhibin and S-100 protein. Interestingly, RNA sequencing identified an in-frame EWSR1-CREM fusion, which was confirmed by subsequent real-time/reverse transcription polymerase chain reaction and fluorescence in situ hybridization assay. Clinical follow-up showed no evidence of recurrence and metastasis. Our pathological findings further expand the phenotypic spectrum of tumors associated with EWSR1-CREM fusions, implying the emergence of a possible novel tumor entity.

Primary pulmonary clear cell sarcoma-the first two reported cases

We report two cases (male patients 50 and 55 years old) of clear cell sarcoma ("melanoma of soft parts") arising in the lung, of which one case showed regional lymph node metastases. Histologically, both tumors displayed varying clear epithelioid and spindle neoplastic cells arranged in storiform and nested growth patterns, separated by thin fibrovascular septa. Immunohistochemical studies demonstrated positive expression of S-100 protein, HMB-45 and Melan-A in one case and S-100 protein only in the other. Fluorescence in situ hybridization showed positive EWSR1 gene rearrangement, and a presence of EWS-ATF1 fusion transcript was confirmed by RT-PCR and sequencing in one case.