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1 An update on immunohistochemical markers in mesenchymal neoplasms By Konstantinos Linos MD, FCAP, FASDP Assistant Professor of Pathology Geisel School of Medicine at Dartmouth Dartmouth-Hitchcock Medical Center Lebanon, NH, USA Financial disclosures Book Royalties A general truth! Some of these markers may prove to be more useful in clinical practice than others With time it is generally appreciated that significant overlap in staining patterns can be seen in different tumor types, some of which share similar biology or can be explained by known biologic mechanisms 1

2 Outline ERG PAX7 DUX4/ETV4 BCOR Claudin 4 STAT6 MUC4 ERG Member of the ETS family of regulatory transcription factors with diverse biological roles Regulates endothelial cell differentiation, angiogenesis, and expression of several endothelial-specific antigens Also required for embryonic stem cells to differentiate into endothelial cells Regulatory gene of cartilage skeletogenesis May have crucial role in permanent cartilage develpment 2

3 ERG in benign vascular tumors ERG in Hemangioendotheliomas 3

4 ERG in angiosarcoma in comparison with CD31 ERG in non epithelial Mesenchymal, Neuroectodermal and Hematopoietic tumors ERG in Epithelial Neoplams 4

5 ERG in nonvascular tumors A hemorrhagic poorly differentiated carcinoma simulating angiosarcoma 5

6 ERG From these studies ERG is positive in >95% of angiosarcomas, with a greater sensitivity compared to CD31 and CD34 ERG usually shows a diffuse pattern of nuclear staining, which facilitates its interpretation in this context. 6

7 Ewing Sarcoma with EWSR1- ERG FLI1 ERG 7

8 Ewing sarcoma with EWSR1-FLI1 EWSR1, FLI1, ERG and their fusion proteins in Ewing Sarcoma 8

9 Leukemia cutis cases Reactive Leukocytic Infiltrates 9

10 10

11 Soft Tissue Chondroma Convetional Chondrosarcoma ERG 11

12 FLI1 ERG Conclusion ERG is therefore a useful marker for confirming endothelial differentiation in both benign and malignant neoplasms Potentially useful marker to distinguish Leukemia Cutis vs reactive myeloid infiltrates Expression can also be seen in a subset of epithelioid sarcomas and a small percentage of Ewing sarcomas, as well as approximately 45% to 50% of prostatic carcinomas. ERG can be seen in selected bone and soft tissue tumor with cartilaginous differentiation Outline ERG PAX7 DUX4-ETV4 BCOR Claudin 4 STAT6 MUC4 12

13 PAX7 Immunohistochemical detection in tumor cell nuclei of myogenin and MYOD1 currently benchmark for rhabdomyosarcoma diagnosis Sensitivity and specificity even in combination is imperfect Negative or focal myogenin in a considerable number of embryonal rhabdomyosarcomas MYOD1: high background and cytoplasmic staining PAX7 PAX7 is a paired box transcription factor required for mammalian skeletal muscle stem cells (aka satellite cells) It plays a critical role in mammalian myogenesis Controls early lineage specification, whereas MYOG and MYOD1 regulate subsequent lineage commitment 13

14 Embryonal Rhabdomyosarcoma 14

15 Embryonal Rhabdomyosarcoma Alveolar Rhabdomyosarcoma 15

16 PAX7 and Rhabdomyosarcoma Potential diagnostic value of PAX7 IHC in the evaluation of rhabdomyosarcoma, especially embryonal rhabdomyosarcoma Less sensitive in ARMS Could be used secondarily in desmin+, MYOG/MYOD1 - cases 16

17 Ewing Sarcoma CIC-DUX4 PAX7 a sensitive marker for Ewing Sarcoma Positive in NKX2-2 negative cases Also positive in both common and variant forms of Ewing Sarcoma PAX7 expression differentiates Ewing Sarcoma from CIC-DUX4 sarcoma What accounts for the robust PAX7 expression in Ewing Sarcoma? EWSR1-FLI fusion protein binds at position 5 to the PAX7 promoter 17

18 Undifferentiated small round cell or spindle-cell tumor PAX7 positivity: Rhabdo vs Ewing Sarcoma Positivity for desmin, MYOG, MYOD1 would strongly favor rhabdomyosarcoma Rare cases of ES can express myogenic features Diffuse membranous CD99 would favor ES Can be positive in rhabdomyosarcomas NKX2.2 would support ES WT1+, PAX7- would support CIC-DUX4 To date IHC focused on the aberrant expression of one of the genes involved in the pathogenic translocation WT1 in DSMRCT (EWSR1-WT1) STAT6 in SFT (NAB2-STAT6) FLI1 in Ewing Sarcoma (ESWR1-FLI1) BCOR in undifferentiated sarcomas PAX7 in ES exploits a characteristic transcriptional read-out of the diseasecausing translocation 18

19 Outline ERG PAX7 DUX4 & ETV4 BCOR Claudin 4 STAT6 MUC4 DUX4 IHC Emerging undifferentiated sarcomas resembling but distinct from Ewing Sarcoma t(4;19) translocation involving CIC-DUX4 t(10;19) translocation CIC-DUX4L Distinct transcriptional signature with poor clinical outcomes 19

20 CD99 WT1 FISH CIC Ewing Sarcoma Malignant Rhabdoid Synovial Sarcoma Tumor 20

21 21

22 ETV4 (ETS Variant 4) Member of the PEA3 subgroup in the ETS transcription factor family Upregulation of WT1 and ETV1/4/5 in CICrearranged sarcomas 22

23 23

24 ETV4 and round cell sarcomas Sensitive but not entirely specific for CICrearranged sarcomas Diffuse, moderate-to-strong expression in ~90% sensitive and 95% specific Outline ERG PAX7 DUX4 & ETV4 BCOR Claudin 4 STAT6 MUC4 24

25 BCOR (BCL-6 interacting corepressor) A subset of undifferentiated round cell sarcomas: BCOR-CCNB3 BCOR-MAML3 ZC3H7B-BCOR YWHAE-NUTM2B BCOR internal tandem duplication (ITD) Clear cell sarcoma of the kidney Primitive myxoid mesenchymal tumor of infancy 25

26 BCOR and Synovial Sarcoma 26

27 27

28 BCOR BCOR IHC is highly sensitive in identifying sarcomas with BCOR abnormality Triage for further molecular tests Avoid extensive IHC and molecular workups in small specimens Synovial sarcoma should be included in the DDx of round cell sarcomas with BCOR+ 28

29 Outline ERG PAX7 DUX4 & ETV4 BCOR Claudin 4 STAT6 MUC4 Claudin 4 and SWI/SNF complex-deficient tumors Claudins are integral components of tight junctions which for barriers in epithelial, endothelial and perineurial cells Claudin 4 is expressed in most epithelial cells and carcinomas Has been validated as a useful marker in the distinction of mesothelioma (lack of expression) from metastatic adenocarcinoma (consistently +) Claudin 4 It has been observed: Epithelial component of biphasic synovial sarcoma Subset of Desmoplastic Small Round Cell Tumor 29

30 SWI/SNF complex Fundamental role in regulation of gene expression Tumor suppressor properties SMARCB1 (INI-1) SMARCA2 (BRM) SMARCA4 (BRG1) ARID1A SWI/SNF complex SMARCB1 deficiency (INI1 loss) Malignant Rhabdoid Tumor Epithelioid Sarcoma Subset of myoepithelial carcinomas Epithelioid MPNST SMARCA4 deficiency (BRG1 loss) Nearly all cases of ovarian small cell carcinomas of hypercalcemic type ARID1A deficiency ~half of ovarian clear cell carcinomas 30

31 Epithelioid Sarcoma Epithelioid Angiosarcoma Epithelioid MPNST Biphasic Synovial Sarcoma 31

32 Ovarian Clear Cell Carcinoma Pancreatic Rhabdoid Carcinoma Cecal Rhabdoid Carcinoma INI1- deficient Sinonasal Carcinoma Claudin 4 It may serve as a useful diagnostic adjunct in the distinction of SWI/SNF complex deficient carcinomas from sarcomas with epithelioid morphology Strongly associated with true epithelial differentiation However absence of claudin 4 staining does not entirely exclude carcinoma 32

33 Keratin CD34 SMARCA4 33

34 Outline ERG PAX7 DUX4 & ETV4 BCOR Claudin 4 STAT6 MUC4 STAT6 and Solitaty Fibrous Tumor STAT6 is a member of the STAT family of cytoplasmic transcription factors, which regulate gene expression by transmitting signals to the nucleus and binding to specific DNA promoter sequences NAB2 is a transcriptional corepressor, a regulator of the early growth response 1 (EGR1) transcription factor 34

35 Variable truncation of the repressor domain of NAB2 with replacement by the transcriptional activation domain of STAT6 Subsequent translocation to the nucleus, where it acts as a transcriptional activator resulting in increased proliferation 35

36 Synovial sarcoma STAT6 Cellular spindle cell lipoma STAT6 36

37 Dedifferentiated liposarcoma Pitfall! Presence of STAT6 expression in approximately 7% to 15% of dedifferentiated liposarcomas The staining pattern in dedifferentiated liposarcoma is variable and may be focal or diffuse, weak or medium to strong in intensity, unlike the generally strong diffuse pattern seen in solitary fibrous tumor 37

38 Unlike the predominantly nuclear pattern of staining seen in solitary fibrous tumor, both cytoplasmic and nuclear expression is common in dedifferentiated liposarcoma. Diffuse expression of MDM2 and CDK4 helps favor a diagnosis of dedifferentiated liposarcoma If doubt persists, FISH for MDM2 amplification may also be useful FISH vs PCR Because STAT6 and NAB2 are located close together on the long arm of chromosome 12, FISH to demonstrate rearrangement of the genes is technically challenging and not diagnostically useful Outline ERG PAX7 DUX4 & ETV4 BCOR Claudin 4 STAT6 MUC4 38

39 MUC4 MUC4 is a useful marker for low-grade fibromyxoid sarcoma (LGFMS) and sclerosing epithelioid fibrosarcoma 39

40 Sclerosing epithelioid sarcoma 40

41 Monophasic synovial sarcoma and MUC4 Sclerosing epithelioid sarcoma, MUC4 and carcinoma Importantly, regarding SEF, in which a poorly differentiated carcinoma may fall into the differential diagnosis it should be remembered that MUC4 expression is seen in a variety of different carcinomas, such as pancreaticobiliary carcinomas, breast carcinoma, and colonic adenocarcinoma. NEVER FORGET! The use of all of these markers requires careful clinical correlation and knowledge of the spectrum of staining in other tumor types, as no one marker is 100% sensitive or specific for a given diagnosis 41

42 KonstantinosLin 42