[Histological, immunohistochemical and molecular study of a paratesticular dedifferentiated liposarcoma with inflammatory myofibroblastic tumor-like features]. / Liposarcoma desdiferenciado paratesticular simulando un tumor miofibroblástico inflamatorio. Estudio histológico, inmunohistoquímico y molecular.

We report the histological, immunohistochemical, and molecular findings of a dedifferentiated liposarcoma with inflammatory myofibroblastic tumor-like features occurring in the paratesticular region. Histologically, the dedifferentiated component closely resembled an inflammatory myofibroblastic tumor. The neoplastic cells were positive for smooth muscle actin with focal CD56, CD99, Bcl2 and EMA expression. WT1, calretinin, myogenin, CK(AE1/AE3), desmin, H-caldesmon, CD34, ALK, CKIT, DOG1, MUC4 and STAT6 were negative. MDM2 showed diffuse and strong nuclear positivity in neoplastic cells and fluorescence in situ hybridization (FISH) revealed amplified MDM2 (high level) but no SYT rearrangement. Although a lipomatous component was evident macroscopically, well-differentiated liposarcomatous components were not evident in the section examined. Dedifferentiated liposarcoma can have prominent inflammatory myofibroblastic tumor-like features. Pathologists should be aware of this histological variant in order to avoid misdiagnosing dedifferentiated liposarcoma as inflammatory myofibroblastic tumor or other spindle cell tumors which have different behavioral patterns and treatment requirements.

[Cutaneous Rosai-Dorfman disease with lack of BRAF-V600, KRAS or NRAS mutations: A reactive or neoplastic disorder?] / Enfermedad de Rosai-Dorfman con presentación cutánea y ausencia de mutaciones BRAF-V600, KRAS y NRAS: ¿trastorno neoplásico o reactivo.

Non-Langerhans cell histiocytosis, including Rosai-Dorfman disease (RDD) and xanthogranuloma are rare disorders with occasional overlapping in the histopathological and immunohistochemical (IHC) findings. We report the case of a 53-year-old woman with erythematous-violaceous plaques on the cheeks and edema in the auricular pavilions. A biopsy was performed and the histopathological examination revealed a histiocytic proliferation with emperipolesis characteristic of RDD and lymphoplasmocitic infiltrate. IHC analysis showed S100 and CD68 positivity in the histiocytes but was negative for CD1a, supporting the diagnosis of RDD. Molecular analysis failed to detect BRAF-V600, NRAS or KRAS mutation. We discuss the differential diagnosis of cutaneous non-Langerhans cell histiocytosis. Pathologist must be aware of unusual presentations of RDD and further treatment options must be explored for patients with unresectable lesions and/or resistance to the classical management of RDD.