Targeted genomic sequencing of follicular dendritic cell sarcoma reveals recurrent alterations in NF-κB regulatory genes

Distinctive Patterns of CTNNB1 (β-Catenin) Alterations in Salivary Gland Basal Cell Adenoma and Basal Cell Adenocarcinoma

Salivary gland basaloid neoplasms are diagnostically challenging. Limited publications report that some basal cell adenomas harbor CTNNB1 mutations, and nuclear β-catenin expression is prevalent. We evaluated β-catenin expression in basal cell adenomas and adenocarcinomas in comparison with salivary tumors in the differential diagnosis and performed targeted genetic analysis on a subset of cases. β-catenin immunohistochemistry was performed on formalin-fixed, paraffin-embedded whole sections from 73 tumors. Nuclear staining was scored semiquantitatively by extent and intensity. DNA was extracted from 6 formalin-fixed, paraffin-embedded samples (5 basal cell adenomas, 1 basal cell adenocarcinoma) for next-generation sequencing. Nuclear β-catenin staining was present in 18/22 (82%) basal cell adenomas; most were diffuse and strong and predominant in the basal component. Two of 3 basal cell adenocarcinomas were positive (1 moderate focal; 1 moderate multifocal). All adenoid cystic carcinomas (0/20) and pleomorphic adenomas (0/20) were negative; 2/8 epithelial-myoepithelial carcinomas showed focal nuclear staining. Most β-catenin-negative tumors showed diffuse membranous staining in the absence of nuclear staining. Four of 5 basal cell adenomas had exon 3 CTNNB1 mutations, all c.104T>C (p.I35T). Basal cell adenocarcinoma showed a more complex genomic profile, with activating mutations in PIK3CA, biallelic inactivation of NFKBIA, focal CYLD deletion, and without CTNNB1 mutation despite focal β-catenin expression. Nuclear β-catenin expression has moderate sensitivity (82%) for basal cell adenoma but high specificity (96%) in comparison with its morphologic mimics. CTNNB1 mutation was confirmed in most basal cell adenomas tested, and findings in basal cell adenocarcinoma suggest possible tumorigenic mechanisms, including alterations in PI3K and NF-κB pathways and transcriptional regulation.

Histiocytic and dendritic cell neoplasms: what have we learnt by studying 67 cases

Tumors derived from histiocytic and dendritic cells encompass a large and heterogeneous group of neoplastic and reactive conditions, and their diagnosis is challenging both for pathologists and clinicians. Diagnosis is based on morphological and phenotypical findings, but hybrid features are not uncommon. Furthermore, recent studies uncovered the molecular mechanisms driving some of these tumors, improving diagnostic adequacy, and providing the basis for effective therapeutic breakthroughs.Sixty-seven cases were submitted to the accessory cell and histiocytic neoplasms session at the European Association of Haematopathology/Society for Hematopathology workshop 2016 held in Basel, Switzerland. The cases included histiocytic sarcomas (HS), Langerhans cell tumors (LCT), Erdheim-Chester disease, interdigitating dendritic cell sarcomas (IDCS), indeterminate dendritic cell tumors (IND-DCT), follicular dendritic cell sarcomas, and blastic plasmacytoid dendritic cell neoplasms. Rosai-Dorfman disease and, more rare, conditions such as ALK-positive histiocytosis were also submitted. These cases illustrated classical and unexpected features at morphological, phenotypical, and molecular levels, providing a valuable compendium for pathologists confronting with these tumors.The paper summarizes the most notable features of every single group of diseases, with comments about the most challenging issues, in the attempt to provide practical indications for their recognition.

Histiocytic sarcoma: New insights into FNA cytomorphology and molecular characteristics

BACKGROUND

Histiocytic sarcoma (HS) is a rare malignant neoplasm showing morphologic and immunophenotypic features of histiocytes. Molecular characteristics of HS and fine-needle aspiration (FNA) criteria for its diagnosis have not been established.

METHODS

A case series of HS in 8 FNA samples from 6 patients was reviewed along with histopathologic and clinical data. Immunohistochemistry was performed on cell blocks (3 cases), core biopsies (5 cases), and surgical specimens (4 cases). Targeted-exome next-generation sequencing (NGS) was performed on surgical resection specimens in 4 cases.

RESULTS

Four patients had a known history of hematolymphoid malignancy. Cytomorphologic features included variably cellular smears composed of large epithelioid cells with reniform nuclei and abundant vacuolated cytoplasm, in an inflammatory background, with occasional cytophagocytosis and lymphoglandular bodies. Marked pleomorphism, multinucleated monster cells, and binucleated histiocytoid cells with partially overlapping, eccentrically placed nuclei resembling Pac-Man were common. Most cases expressed histiocytic markers CD68 (6 of 7 cases), CD163 (5 of 5 cases), and PU.1 (3 of 4 cases). In 3 cases, NGS analysis revealed alterations in lysine methyltransferase 2D (KMT2D)/mixed-lineage leukemia 2 (MLL2), a gene involved in chromatin regulation and previously implicated in the pathogenesis of follicular lymphoma.

CONCLUSIONS

Although diagnosing HS with FNA alone is extremely challenging, the presence of pleomorphic and epithelioid large cells with binucleation and/or multinucleation in an inflammatory background should prompt the diagnosis of HS with judicious use of confirmatory histiocytic lineage markers. The detection of recurrent KMT2D/MLL2 alterations implicates epigenetic regulation in the pathogenesis of HS and supports the notion of transdifferentiation from a genetically similar but phenotypically distinct tumor of a different lineage. Cancer Cytopathol 2017;125:604-14. © 2017 American Cancer Society.

Follicular Dendritic Cell Sarcoma

Follicular dendritic cell sarcoma is a rare tumor that typically arises within lymph nodes but can also occur extranodally. It is important to have a high index of suspicion, so follicular dendritic cell sarcoma is included in the differential diagnosis of a spindle cell neoplasm in the appropriate clinical and morphologic settings. When included in the differential diagnosis, immunohistochemistry is generally sufficient to substantiate the diagnosis of follicular dendritic cell sarcoma. In this review, we discuss the clinicopathologic features of follicular dendritic cell sarcoma, recent molecular and cytogenetic findings, prognosis, and current approaches to treatment.

Characteristics, management, and outcomes of patients with follicular dendritic cell sarcoma

Dendritic cell sarcomas are rare tumours of antigen presenting cells. Data regarding their biology, management and outcomes are sparse. We analysed 66 patients with follicular dendritic cell sarcoma (FDCS). Six patients also had Castleman disease, 9 had another malignancy and 13 had an autoimmune disease. Fifty-four per cent of patients presented with localized disease and 46% with systemic involvement. The median progression-free (PFS) and overall survival (OS) following frontline therapy was 21 and 50 months, respectively. Survival outcomes were significantly inferior in patients with extranodal, bulky or intra-abdominal disease at presentation. Stage was not associated with survival. Management approaches were heterogeneous. Patients who underwent an upfront gross total resection (GTR) experienced better PFS and OS (both P < 0·0001). In patients who underwent a GTR, consolidative radiotherapy was associated with improved local control (P = 0·03), PFS (P = 0·04) and OS (P = 0·05). In patients with measureable disease, gemcitabine with a taxane yielded an overall response rate of 80%. The pattern of relapse was predominantly locoregional. Salvage rates after recurrence were poor. Studies are underway at our institution to define the genomic profile in FDCS and identify potential novel therapeutic targets.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features Accounts for More Than Half of "Carcinomas" Harboring RAS Mutations

BACKGROUND

Molecular testing of thyroid nodules is increasingly being utilized to guide clinical management decisions. RAS mutations are the most frequent mutations detected in the context of an indeterminate fine-needle aspiration (FNA) diagnosis. The term "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) was recently introduced to promote conservative management of tumors previously classified as noninvasive follicular variant of papillary thyroid carcinoma (FVPTC). This change in terminology was based on the indolent clinical behavior of these tumors and their molecular profile, which includes frequent RAS mutations. The aim of this study was to determine the percentage of RAS-mutant "carcinomas" that would now be classified as NIFTPs.

METHODS

A search was performed for cases with known activating RAS mutations in a database of 199 thyroid carcinomas that underwent molecular characterization as part of Profile:Oncopanel between July 2013 and July 2015. Cases of FVPTC were re-reviewed to identify tumors that now would be categorized as NIFTP. Preceding FNA diagnoses were recorded, and cases with an indeterminate FNA result (defined as a diagnosis of atypia/follicular lesion of undetermined significance, suspicious for follicular neoplasm, or suspicious for malignancy) were identified.

RESULTS

A total of 27 RAS-mutant thyroid tumors were identified. Fifteen (56%) cases had an NRAS mutation, nine (33%) had an HRAS mutation, and three (11%) had a KRAS mutation. Twenty-four (89%) cases had a preceding FNA, 19 (79%) of which had an indeterminate FNA diagnosis. The surgical resection specimen demonstrated FVPTC in 20 (74%) cases, classical type PTC in two (7%), solid variant of PTC in one (4%), and follicular thyroid carcinoma in four (15%). Of the 20 FVPTCs, 16 (80%) would now be classified as NIFTP. NIFTPs accounted for 59% of RAS-mutant carcinomas overall and 63% of RAS-mutant carcinomas with a prior indeterminate FNA diagnosis.

CONCLUSION

NIFTPs accounted for more than half of RAS-mutant "carcinomas" in this cohort. In cases where clinical and sonographic data support a low-risk phenotype, these results suggest that a lobectomy should be considered as the initial surgical approach for a nodule with an indeterminate FNA diagnosis and a RAS mutation.

miRNA expression profiling divides follicular dendritic cell sarcomas into two groups, related to fibroblasts and myopericytomas or Castleman's disease

Follicular dendritic cell (FDC) sarcomas are rare mesenchymal tumours, which are fatal in 20% of the patients and usually occur in secondary lymphoid organs or extranodal localizations. Due to the rareness of these tumours, only few studies have been conducted on molecular level. In the present study, we performed microRNA (miRNA) profiling of 31 FDC sarcomas and identified two subgroups, one with high miRNA expression and the other group with low miRNA expression levels. The first group showed a strong similarity to fibroblasts and myopericytomas, whereas the second group was more closely related to FDCs from Castleman's disease. Both groups showed important differences compared with myeloid-derived dendritic cells, confirming mesenchymal origin of FDCs and their derived sarcomas. The two FDC sarcoma groups did not differ on morphological grounds, mitotic activity or BRAF mutation status. However, patients of group I presented a tendency to a shorter overall survival and more frequent podoplanin expression by immunohistochemistry. The importance of these newly recognized FDC sarcoma subgroups in terms of clinical behaviour and therapeutic implications should be assessed in a larger cohort in future studies.

Treatment of breast cancer 2 (BRCA2)-mutant follicular dendritic cell sarcoma with a poly ADP-ribose polymerase (PARP) inhibitor: a case report

BACKGROUND

Follicular dendritic cell sarcoma is a rare tumour with clinical behaviour covering a spectrum from indolent to aggressive disease. Treatment recommendations are currently based on case reports and small series describing combinations of surgery, chemotherapy and radiotherapy providing the best patient outcomes. Recent knowledge on molecular aberrations in this disease have not yet impacted on therapeutic decisions.

CASE PRESENTATION

We describe a case of progressive follicular dendritic cell sarcoma of the lung and pleura, treated based on knowledge of the tumour's molecular aberrations. The patient was initially treated with surgery, chemotherapy and radiotherapy and developed disease progression. Mutation testing by Caris molecular intelligence demonstrated a breast cancer 2 gene mutation and further treatment with carboplatin and veliparib achieved disease stabilisation.

CONCLUSION

Understanding of the molecular profile of rare tumours is key to improve therapeutic decision making and patient outcomes.