Dysplastic lipoma

Dysplastic lipoma
Terminology that acknowledges the cytomorphologic, immunohistochemical, and molecular genetic abnormalities
Positions the tumor midway in the spectrum between conventional lipoma and MDM2 gene amplified atypical lipomatous tumors

1. WHO 4 th Edition – 2003

2. Lipoma Minimal variation in size Lobules separated by thin fibrovascular septae Atypical lipomatous tumor Absence of MDM2 amplification Variation in size Lobules separated by spindle cells and cells with marked nuclear atypia MDM2 amplification

3. Patient with a swelling over back, having smooth borders and a positive slip sign

4. Globular mass with a yellow greasy cut surface

5. Variation in shape and size Lochkern cells with atypia Binucleation

6. Are we dealing with an “ATYPICAL LIPOMATOUS TUMOR” ? Let’s do FISH  I am sure MDM2 will be amplified !

7. MDM2 NOT AMPLIFIED ! What now ?

8. NO sweat ! Let’s give it A NEW NAME !

9. Dysplastic Lipoma Michael Michal, Abbas Agaimy , Alejandro Luiña Contreras, Marian Svajdle Dmitry V. Kazakov , Petr Steiner, Petr Grossmann,Petr Martinek , Ladislav Hadravsky , Kvetoslava Michalova , Peter Svajdler , Zoltan Szep , Michal Michal , and John F. Fetsch Am J Surg Pathol Volume 42, Number 11, November 2018

10. Charles University, Pilsen Charles University, Prague Friedrich-Alexander University, Nürnberg Louis Pasteur University, Kosice Cytopathos Ltd, Bratislava

11. 66 cases were retrieved Authors searched their registries for : Anisometric cell lipoma Lipoma with mild atypia of uncertain significance ALT variant

12. Immunohistohemistry done on Ventana BenchMark ULTRA Antibody Clone Dilution Company CD34 QBEnd /10 1:200 Dako , Glostrup , Denmark Retinoblastoma 1 (RB1) protein G3- 245 1:50 BD Biosciences, Franklin Lakes, NJ MDM2 1F2 1:100 Thermo Fisher Scientific, Rockford, IL P16 E6H4 Prediluted Ventana Medical System Inc. CDK4 DCS-156 1:100 Zytomed CD163 MRQ-26 Prediluted Cell Marque, Rocklin, CA S100p Polyclonal Prediluted Ventana Medical System Inc.

13. One hundred randomly selected nonoverlapping tumor cell nuclei were evaluated in all analyzed samples Criteria for positivity on FISH M DM2 amplification ( ZytoLight SPEC MDM2/CEN 12 Dual Color Probe) Ratio of MDM2 probe signals to corresponding chromosome 12 centromeric probe signals was ≥ 2.0 RB1 loss (Mix of SureFish 13q14.2 RB1 and Vysis CEP 17 probes ) Number of cells with loss divided by the total number of cells counted >45% of nuclei had only one signal per nucleus

14. DNA extraction and mutation analysis by Sanger sequencing of coding exons for the TP53 gene Primers designed against known single-nucleotide polymorphisms in TP53 gene

15. Next Generation Sequencing Panel of genes including TP53, RB1, and MDM2 QIAseq technology (Qiagen, Hilden, Germany) Illumina’s Nextseq . 500 system

16. 22 to 87 years (mean: 51.2 y) Gender (male predominant)

17. All subcutaneous site Head and neck Upper back shoulders and posterior neck Inguinal region

18. 1.5 to 14 cm in the greatest dimension Mean size of 5.2 cm. Size

19. Synchronous or Metachronous

20. All were removed by simple excision Follow-up available for 47 patients Follow-up interval of 27.3 months (range: 1 to 192 months) Two individuals (4.2%) experienced a local recurrence 1 at 7 months and 1 at 44 months There were no metastases

21. Well-circumscribed and had a lobular contour Adipocytic size variation Single-cell fat necrosis Collagenous stroma was sparse and thick ropy collagen bundles were absent

22. Lochkern cells Binucleation Histiocyte Coarse chromatin

23. P53 immunostain 2% to 20% of the adipocytic nuclei Had a strong tendency to highlight the most atypical cells

24. S100 protein was always positively expressed by most adipocytes No case showed CDK4 immunostaining CD34 highlighted some spindled stromal cells Usually sparse More substantial than appreciated in H & E sections

25. 20 out of 50 cases tested had adipocytic nuclei with immunoreactivity for MDM2 In most cases, <1% of the nuclei were positive But in 4 cases, as many as 10% of cells were immunoreactive

26. Of the 32 tested cases, 22 showed a deficiency of RB1 protein expression in almost all lesional cells Remaining 10 cases, RB1 showed a partial loss of expression by the tumor cell population

27. p16 immunostaining was difficult to interpret Increased interobserver variability 5% to 20% cytoplasmic and nuclear immunoexpression by tumor cells, including those with nuclear atypia

28. CD163 was expressed by histiocytes and helped differentiate these cells from the atypical fat cells

29. MDM2 FISH was negative in all 60 analyzable cases, including those with MDM2 immune expression RB1 heterozygous gene deletion, as defined in this study by was present in 3 of 13 cases All 5 tested cases showed no TP53 mutations

30. Most samples had low DNA quality with an unfavorable ratio of sequenced reads and did not reach the expected limit of detection of at least 25% and were therefore excluded from analysis Only 3 samples showed detectable variants in the KMT2D, PAK3, SETD2, SUZ12, PDGFRA, and FGFR4. However, their clinical significance was not available in the ClinVar database.

31. DISCUSSION

32. Evans et al proposed: Atypical lipoma for tumors located in the soft tissue of the extremities Well-differentiated liposarcoma for those found in the retroperitoneum The definition of ALT/WDL was and still is largely based on morphologic features: Significant variation in cell size At least focal adipocytic nuclear atypia Nonlipogenic stromal cell atypia Lipoblasts may contribute to the morphologic diagnosis but are not a requisite feature Genetic standpoint: most ALT/WDLs are characterized by a supernumerary ring or giant marker chromosome which contains amplified sequences of MDM2 (12q15)

33. MDM2 gene amplification defines the ALT category There are a variety of other well-differentiated fatty tumors that lack MDM2 gene amplification that can still be reasonably viewed from a biologic/clinical perspective as ALT variants Convincing adipocytic atypia Some potential for local recurrence Lack of metastatic potential

34. Analyzing the concordance between expert morphologic assessment and MDM2 status have noted discrepancies Lipoma and lipoma-like ALT is one of the most common diagnostic dilemmas solved by soft tissue pathology consultants Subgroup of microscopically equivocal well-differentiated lipomatous neoplasms that elude definitive histological diagnosis “Dysplastic lipoma” - represents a major constituent of this category

35. Strong male predominance 66 cases Broad age range at presentation Striking predilection for upper back, shoulders and posterior neck region Tendency for multifocality Infrequent association with a pediatric history of retinoblastoma

36. Adipocytic size variation and patchy single-cell fat necrosis Distinctive morphology Spindled stromal cells and collagenous matrix tend to be scant or absent Adipocytes with one or more atypical nuclei are always present Atypical adipocytes have enlarged variably sized nuclei with coarsened chromatin, small nucleoli, and often focal Lockhern change

37. Overexpression of p53 Always present Not uniformly expressed Tendency to highlight the abnormal adipocytic nuclei RB1 gene abnormalities are an additional noteworthy feature MDM2 immunoexpression can be present Typically limited and focal finding Expression levels usually less than p53 Importantly, FISH analysis for MDM2 gene amplification is consistently negative

38. Mononucleated and multinucleated histiocytes can occasionally be confused with atypical adipocytes They tend to have dark-staining reniform or oval nuclei Finely vacuolated or slightly granular eosinophilic cytoplasm In doubt, immunostaining for CD163 and CD68 can be helpful Authors’ suspect cellular dysplasia contributes to the development of single cell fat necrosis in dysplastic lipomas p53 immunoexpression , by itself, does not distinguish dysplastic lipoma from a conventional- type ALT Up to half of ALT will have focal p53 expression Can also be seen, on occasion, in other fatty tumors with atypia - Authors’ data suggests RB1 gene abnormalities are a likely oncogenic event in dysplastic lipomas - Not clear what role, if any, TP53 and MDM2 play in the formation of these tumors

39. Authors consider the follow-up data insufficient to reliably assess the biological behavior of dysplastic lipomas There is no evidence, at present, that dysplastic lipomas have potential for dedifferentiation over time, and there is no metastatic potential Nevertheless, when drawing on all available data, the recurrence rate for this tumor appears to be at least 8%, Higher than that expected for a conventional subcutaneous lipoma Less than what would generally be expected for a subcutaneous conventional- type (MDM2 amplified) atypical lipomatous tumor

40. Authors proffer the epithet “Dysplastic lipoma,” Terminology that acknowledges the cytomorphologic, immunohistochemical, and molecular genetic abnormalities Positions the tumor midway in the spectrum between conventional lipoma and MDM2 gene amplified atypical lipomatous tumors