[Cutaneous Rosai-Dorfman disease with lack of BRAF-V600, KRAS or NRAS mutations: A reactive or neoplastic disorder?].

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.

Machado I ，Alcacer Fernández-Coronado J ，Requena C ，Través V ，Latorre Martínez N ，Ortega J ，Requena L ，Alcacer García J ... -  《-》

Primary Rosai-Dorfman disease of the central nervous system: A clinical, histological, and molecular appraisal.

Parkhi M ，Chatterjee D ，Kashyap D ，Aggarwal A ，Radotra B ... -  《-》

Rosai-Dorfman Disease Harboring an Activating KRAS K117N Missense Mutation.

Shanmugam V ，Margolskee E ，Kluk M ，Giorgadze T ，Orazi A ... -  《-》

Cutaneous adult xanthogranuloma with a small portion of BRAF(V) (600E) mutated Langerhans cell histiocytosis populations: A case report and the review of published work.

Histiocytoses, including Langerhans cell histiocytosis (LCH), juvenile or adult xanthogranuloma (AXG) and Rosai-Dorfman disease (RDD), are rare disorders characterized by the proliferation of cells derived from monocyte/macrophage lineages. A few cases of LCH coexisting with xanthogranuloma or RDD have been reported. The etiology of these diseases remains unclear. However, oncogenic BRAFV 600E mutations have been identified in LCH. Here, we report the case of a 26-year-old Japanese man with a 3-month history of a solitary occipital nodule. No abnormality was detected in his other organs, and a total resection of the nodule was performed. Histopathological examination revealed the coexistence of LCH and AXG with prominent emperipolesis characteristic of RDD. Immunohistochemistry showed that most of the large histiocytes were positive for CD68, weakly positive or negative for S100, and negative for CD207 and CD1a, supporting the diagnosis of AXG. The tumor cells with emperipolesis did not show S100-positive findings characteristic of RDD. The focally aggregated oval histiocytic cells were positive for CD1a, CD207, CD68 and S100, and were compatible with the immunophenotype of LCH cells. In addition, these cells were positive for BRAFV 600E mutation. The tumor cells in our patient exhibited a cellular morphology characteristic of multiple histiocytoses in a solitary cutaneous nodule, which may imply an etiological association among LCH, AXG and RDD. To our knowledge, this is the first report of a BRAFV 600E mutation-positive case of LCH coexisting with AXG. Because patients with BRAFV 600E mutation have higher risks of multisystemic LCH and recurrence, we should carefully follow up the patient.

Ishikawa M ，Endo Y ，Uehara A ，Suto M ，Yasuda M ，Motegi SI ，Ishikawa O ... -  《-》

KRAS 117N positive Rosai-Dorfman disease with atypical features.

Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is a rare disease typically characterized by a histiocytic proliferation within lymph nodes, which is due to an unknown etiology. Extranodal involvement can occur, and it more rarely can involve the skin. RDD generally presents with an indolent nature and follows a benign disease course, although more aggressive cases have been reported. The condition predominately affects children and young adults. It is classically characterized by massive, bilateral painless lymphadenopathy and accumulation of CD68-positive, S100-positive, CD1a-negative histiocytes, with the presence of emperipolesis as a hallmark. Herein, we present an aggressive case in a 76-year-old male with past medical history significant for prostate cancer, who presented with a 7-month history of lymphadenopathy and new onset of multiple large abdominal wall, cutaneous, lymph node, liver, and lung masses, all of which were histopathologically atypical, but showed features consistent with RDD, including emperipolesis and strong S100 positivity. Molecular studies showed a KRAS 117N mutation, which has been recently reported in RDD. While most cases present as a benign tumor, this case demonstrated aggressive features clinically, showed partial response to MEK inhibitor immunotherapy in the setting of a KRAS mutation, and demonstrated atypical cytologic features on histopathology.

Jafri ZA ，Reddy SP ，Cassarino DS 《-》