Solitary fibrous tumor: a case series identifying pathological adverse factors—implications for risk stratification and classification Abstract Solitary fibrous tumors (SFTs) are a rare type of mesenchymal lesion in which specific clinicopathologic factors have been related to patient outcome. We collected clinical, pathological, and molecular data of 28 patients with histologically confirmed SFT having at least one pathological factor associated with aggressive behavior. Molecular analysis to detect NAB2/STAT6 gene fusion, TP53, and/or TERT promoter mutation was performed. We analyzed the pathological factors predictive of recurrence/metastasis and compared with clinical outcome. The risk of metastasis was calculated using four previously described scoring systems. Histopathologically, all tumors revealed hypercellularity, 11 had ≥ 4 mitoses/10 HPF, and 12 showed necrosis. Dedifferentiation was observed in three tumors. STAT6 was positive in all cases. Desmin, p16, INSM1, and HTER immunoexpressions were detected in 14, 18, 21, and 46% of the SFT, respectively. The NAB2/STAT6 gene fusion was detected in 16 tumors. After a median follow-up of 34 months, 32.0% recurred, 32.1% metastasized, and 35.7% died of disease. TERT mutations were detected in almost half the tumors. Tumors with TP53 mutations or with TP53 and TERT promoter mutations were almost always classified as high risk, and the patients developed metastases and/or died of disease. Tumors with intermediate-risk and TERT mutation had a worse evolution. SFTs with adverse pathological parameters were not always related with a poor outcome, thus confirming the unpredictable clinical behavior of SFT. The inclusion of molecular factors (TP53 and TERT promoter status) may provide new prognostic indicators for future risk stratification systems, especially in the intermediate-risk group.

The broad and challenging landscape of extranodal lymphoproliferations Abstract Two sessions in the workshop of the 19th meeting of the European Association for Haematopathology termed “challenging extranodal lymphoproliferations” and “extranodal non-site-specific lymphoproliferations”, dealt with a series of heterogenous cases. These included lymphoproliferations of all cell lineages, from reactive lesions mimicking lymphomas through indolent lymphoid neoplasia and tumours with unclear biological behaviour to aggressive and transformed lymphomas. The themes addressed included cases with borderline features between hyperplastic and neoplastic lesions, the diagnostic spectrum of IgG4-related disease, T cell lymphoproliferations arising in extranodal sites with presumed indolent behaviour, diverse clinical presentations of intravascular large B cell lymphoma, diagnostic problems encountered with tumours displaying plasmablastic morphology, pitfalls concerning rare entities like adult T cell lymphoma/leukaemia (ATLL) and extranodal natural killer/T cell (NK/T) lymphomas, and unusual clinical presentations of various lymphomas. Altogether, within the frame of these two sessions, 75 cases remarkably differing in their clinical background, genetic features and overall need for a meticulous diagnostic approach were presented and discussed. In this paper, the salient points raised during the discussion of the cases, current diagnostic concepts and recommendations relevant to the diagnosis of these lymphoproliferations are described.

Histomorphologic assessment and distribution of high-risk human papillomavirus (HPV) types in cervical high-grade squamous intraepithelial lesions with unusual histomorphologic features Abstract In rare cases, equivocal histomorphology (‘deceiving dysplasia’) does not allow immediate diagnosis of cervical high-grade squamous intraepithelial lesion (HSIL). We studied whether these cases are correlated with specific high-risk human papillomavirus (hr HPV) types. During 2011–2017, 39 cases of p16-positive cervical tissue biopsies with unusual (‘deceiving’) dysplastic histomorphology were identified and matched with the same number of controls (typical HSIL samples). Histomorphological characteristics were reviewed blindly and HPV testing was performed using the clinically validated RealTime test (Abbott) and Anyplex HPV 28 (Seegene). HPV 16 and HPV 31 were the two most frequent HPV types in both groups, although minimum, proportional, hierarchical and any etiological attribution estimates for HPV 16 were significantly lower in the deceiving group (13.2%, 21.3%, 23.7% and 23.7%) than in the control group (32.4%, 48.1%, 48.6% and 48.6%). In addition, the distribution of other hr HPV types differed between the two study groups, with five HPV types (HPV 56, 58, 59, 73 and 82) detected only in the deceiving group. Histomorphologic review of both groups (regardless of HPV type) confirmed significant differences in nuclear atypia, maximum lesion thickness and cellularity, although these were diminished when cross-comparisons between HPV16/18 and non-HPV16/18 cases pooled from both study groups were evaluated. Different attribution estimates for HPV 16, HPV 16/18 and non-16/18 hr HPV types in deceiving and control groups were observed, in particular for HPV 16. However, an unusual (deceiving) histomorphology may also depend on unknown HPV-related molecular changes.

Update on selected advances in the immunohistochemical and molecular genetic analysis of soft tissue tumors Abstract Although traditional morphological evaluation remains the cornerstone for the diagnosis of soft tissue tumors, ancillary diagnostic modalities such as immunohistochemistry and molecular genetic analysis are of ever-increasing importance in this field. New insights into the molecular pathogenesis of soft tissue tumors, often obtained from high-throughput sequencing technologies, has enabled significant progress in the characterization and biologic stratification of mesenchymal neoplasms, expanding the spectrum of immunohistochemical tests (often aimed towards recently discovered genetic events) and molecular genetic assays (most often fluorescence in situ hybridization and reverse transcription-polymerase chain reaction). This review discusses selected novel molecular and immunohistochemical assays with diagnostic applicability in mesenchymal neoplasms, with emphasis on diagnosis, refinement of tumor classification, and treatment stratification.

Compound blue nevus: a reappraisal of the concept in the genomic era Abstract We report a series of 21 compound blue nevi, a rare variant in the vast clinical and morphological spectrum of blue melanocytic proliferations. Clinically, they presented in young adults, with a slight female predominance. One-third were located on the dorsum of the foot. Morphologically, all cases displayed large dendritic melanocytes restricted to the deep layers of the epidermis. The compound component was central and evenly distributed. Melanocytic density ranged from scarce isolated cells to a confluent lentiginous architecture. In 12 of the 21 cases, junctional nests of small, bland, weakly pigmented melanocytes were associated. These nests became confluent in the most cellular cases. In all cases, a dermal component was immediately present underneath, mainly of cellular blue nevus-type. All cases were genetically confirmed to harbor either a GNAQ or GNA11 hotspot mutation. This study expands the morphological spectrum of blue nevi that should not be restricted to a strictly intradermal melanocytic proliferation.

What’s new in bone forming tumours of the skeleton? Abstract Bone tumours are difficult to diagnose and treat, as they are rare and over 60 different subtypes are recognised. The emergence of next-generation sequencing has partly elucidated the molecular mechanisms behind these tumours, including the group of bone forming tumours (osteoma, osteoid osteoma, osteoblastoma and osteosarcoma). Increased knowledge on the molecular mechanism could help to identify novel diagnostic markers and/or treatment options. Osteoid osteoma and osteoblastoma are bone forming tumours without malignant potential that have overlapping morphology. They were recently shown to carry FOS and—to a lesser extent—FOSB rearrangements suggesting that these tumours are closely related. The presence of these rearrangements could help discriminate these entities from other lesions with woven bone deposition. Osteosarcoma is a malignant bone forming tumour for which different histological subtypes are recognised. High-grade osteosarcoma is the prototype of a complex karyotype tumour, and extensive research exploring its molecular background has identified phenomena like chromothripsis and kataegis and some recurrent alterations. Due to lack of specificity, this has not led to a valuable novel diagnostic marker so far. Nevertheless, these studies have also pointed towards potential targetable drivers of which the therapeutic merit remains to be further explored.

MDM2-positive papillary sarcomatoid renal cell carcinoma: a potential diagnostic pitfall Abstract Sarcomatoid renal cell carcinoma is a highly aggressive form of carcinoma, histologically showing both carcinomatous and mesenchymal component in different proportions. We present a case of advanced type 1 papillary sarcomatoid renal cell carcinoma infiltrating adjacent organs and showing positivity for MDM2 by immunohistochemistry and MDM2 amplification by fluorescence in situ hybridization. This finding, together with sarcomatoid morphology, poses a potential pitfall for diagnosis with dedifferentiated liposarcoma. MDM2 is known to be altered in various human sarcomas. Only recently, MDM2 alterations have been reported in carcinomas. The presented case illustrates the need of thorough sampling with clinic-pathological correlation before making a final diagnosis in sarcomatoid retroperitoneal tumours. Additionally, the potential clinical implications of MDM2 amplification in renal cell carcinoma are discussed.

PAX8 expression in anaplastic thyroid carcinoma is less than those reported in early studies: a multi-institutional study of 182 cases using the monoclonal antibody MRQ-50 Abstract Anaplastic thyroid carcinoma (ATC) is an aggressive malignant tumor composed of undifferentiated thyroid follicular cells. Pathological diagnosis of ATC can be challenging as the tumor may show morphological overlap with other neoplasms with anaplastic morphology. Immunohistochemical demonstration of thyroid origin facilitates the diagnosis of ATC. Previous studies using the polyclonal anti-PAX8 antibody 10336-1-AP suggested that PAX8 was the most sensitive marker, expressed in up to 80% of ATC. According to a 2018 NordiQC report, the monoclonal anti-PAX8 antibody MRQ-50 has become the most commonly used anti-PAX8 antibody worldwide. However, validation of this antibody in ATC is lacking. In this study, we recruited 182 ATC cases from seven institutions. Pathology slides were subjected to histology review. PAX8 immunohistochemistry using the MRQ-50 antibody was performed in whole tissue slides (n = 147) or tissue microarray sections (n = 35). We found PAX8 expression in 54.4% of the cases, which was significantly lower than those reported in prior studies with the polyclonal antibody. PAX8 expression was positively correlated with the presence of an epithelial pattern (63.6% vs 37.5%, p = 0.0008) and a coexisting differentiated thyroid carcinoma component (71.6% vs 44.3%, p = 0.0004), but was not associated with age, gender, specimen type, or presence of giant cell and sarcomatoid patterns. In conclusion, we demonstrated PAX8 expression using the monoclonal antibody MRQ-50 in only half of the cases in a large ATC series. Pathologists should be aware that PAX8 expression in ATC is less than those reported in early studies to avoid misdiagnosis.

Different histological types of active intraplaque calcification underlie alternative miRNA-mRNA axes in carotid atherosclerotic disease Abstract Arterial calcification is an actively regulated process, with different morphological manifestations. Micro-RNAs emerged as potential regulators of vascular calcification; they may become novel diagnostic tools and be used for a finest staging of the carotid plaque progression. The present study aimed at characterizing the different miRNA-mRNA axes in carotid plaques according to their histological patterns of calcification. Histopathological analysis was performed on 124 retrospective carotid plaques, with clinical data and preoperatory angio-CT. miRNA analysis was carried out with microfluidic cards. Real-time PCR was performed for selected miRNAs validation and for RUNX-2 and SOX-9 mRNA levels. CD31, CD68, SMA, and SOX-9 were analyzed by immunohistochemistry. miRNA levels on HUVEC cells were analyzed for confirming results under in vitro osteogenic conditions. Histopathological analysis revealed two main calcification subtypes of plaques: calcific cores (CC) and protruding nodules (PN). miRNA array and PCR validation of miR-1275, miR-30a-5p, and miR-30d indicated a significant upregulation of miR-30a-5p and miR-30d in the PN plaques. Likewise, the miRNA targets RUNX-2 and SOX-9 resulted poorly expressed in PN plaques. The inverse correlation between miRNA and RUNX-2 levels was confirmed on osteogenic-differentiated HUVEC. miR-30a-5p and miR-30d directly correlated with calcification extension and thickness at angio-CT imaging. Our study demonstrated the presence of two distinct morphological subtypes of calcification in carotid atheromatous plaques, supported by different miRNA signatures, and by different angio-CT features. These results shed the light on the use of miRNA as novel diagnostic markers, suggestive of plaque evolution.

Clinicopathologic features of Buschke-Löwenstein tumor: a multi-institutional analysis of 38 cases Abstract Buschke-Löwenstein tumor (BLT) is a rare sexually transmitted disease, mostly described in clinical literature as case reports or small series. Here, we investigated the clinicopathologic features of BLT in a total of 38 cases retrieved from multiple academic institutions. The average age was 47.6 ± 12.8 (mean ± SD) years old at diagnosis. The male to female ratio was 4.4:1. Common presenting symptoms were pain/discomfort, bleeding, mass lesion, and discharge. It was frequently linked to smoking and positive human immunodeficiency virus status. The tumor size and thickness were 8.5 ± 6.6 cm and 1.5 ± 1.3 cm, respectively. Histologically, 19 (50%) cases had an invasive squamous cell carcinoma component and were associated with high-risk human papillomavirus infection. There was no lymphovascular or perineural invasion, or nodal metastasis at initial diagnosis. BLTs with invasion had higher frequency of dyskeratosis, neutrophilic microabscesses, and abnormal mitoses, but lower frequency of pushing border compared with BLTs without invasion. All patients underwent wide excision, and some also received chemoradiation therapy. After a median follow-up of 23 months (range 1–207), the recurrence rate was 23.7% and disease-specific mortality was 2.6%. In summary, we presented the largest case series of BLT to date to characterize its unique clinicopathologic features. Our study indicated that certain histologic features such as dyskeratosis, neutrophilic microabscess, and abnormal mitosis in the non-invasive portion may be important clues on lesional biopsy to predict the presence of underlying invasive carcinoma.