Superficial CD34 Positive Fibroblastic Tumour with Myxoid Stroma.

Superficial CD34 positive fibroblastic tumor is a rare low-grade neoplasm of the skin and subcutis with indolent behavior. This entity has been included in the current World Health Organisation (WHO) classification of soft tissue tumors. Pathological diagnosis can be challenging due to significant morphological overlap with other entities and the large spectrum of CD34 positive tumors. We report a case in a twenty-five male which showed characteristic diagnostic features, but in addition showed myxoid stroma. The presence of myxoid stroma has not been previously emphasized in this entity and broadens the histologic differential diagnosis significantly to include myxoid soft tissue tumors. A subset of these tumors harbor PRDM10-rearrangements, but a defining molecular feature has not yet been described, highlighting the need for further molecular characterization of this potentially genetically heterogenous tumor. Awareness of this entity among surgeons and pathologists is important to prevent misclassification as an aggressive sarcoma and avoid over-treatment.

HIV, Placental Pathology, and Birth Outcomes-a Brief Overview.

The spectrum of placental pathology in human immunodeficiency virus (HIV) is vast. Features observed are not only limited to the effects of the virus itself but may include that of coinfections such as tuberculosis and syphilis. The presence of other comorbidities and changes as a result of antiretroviral therapy may further confound the histologic findings. There is a paucity of unbiased information of the effects of maternal HIV on the placenta and how these changes relate to birth outcomes. Antiretroviral therapy, now in widespread use, has altered the course of maternal HIV disease and it is unknown whether this has altered the pathophysiology of HIV on the placenta. HIV-associated placental findings that have been most well described include acute chorioamnionitis, low placental weight, and maternal vascular malperfusion, with a tendency towards lower rates of chronic villitis.

Gene of the month: IDH1.

Isocitrate dehydrogenase 1 (IDH1) encodes a protein which catalyses the oxidative decarboxylation of isocitrate to α-ketoglutarate. Mutant IDH1 favours the production of 2-hydroxyglutarate, an oncometabolite with multiple downstream effects which promote tumourigenesis. IDH1 mutations have been described in a number of neoplasms most notably low-grade diffuse gliomas, conventional central and periosteal cartilaginous tumours and cytogenetically normal acute myeloid leukaemia. Post zygotic somatic mutations of IDH1 characterise the majority of cases of Ollier disease and Maffucci syndrome. IDH1 mutations are uncommon in epithelial neoplasia but have been described in cholangiocarcinoma.

Rosai-Dorfman disease: an overview.

CONTEXT: Rosai-Dorfman disease is an uncommon histiocytic disorder most frequently presenting as bilateral cervical lymphadenopathy in children and young adults. Extranodal disease occurs in a significant proportion of patients. It has been recently classified as part of the 'R group' of histiocytoses by the Histiocyte Society in 2016. Cutaneous Rosai-Dorfman disease is regarded as a separate disease entity that falls into the 'C group' of histiocytoses according to this classification system. The pathogenesis was previously poorly understood; however, recent evidence demonstrating clonality in a subset of cases raises the possibility of a neoplastic process. A possible association with IgG4-related disease remains controversial. OBJECTIVES: To provide a comprehensive review of Rosai-Dorfman disease, including nodal, extranodal and cutaneous forms, with a particular emphasis on new insights into the possible clonal nature of the disease; to discuss the recently revised classification of the histiocytoses by the Histiocyte Society; and to summarise the findings from the literature regarding the controversial association with IgG4-related disease. DATA SOURCES: This review is based on published peer-reviewed English literature. CONCLUSIONS: Classic Rosai-Dorfman disease, which may be sporadic or familial, is considered a separate entity from cutaneous disease, which is reflected in the revised classification of histiocytoses. An increase in IgG4-positive plasma cells may be seen in Rosai-Dorfman disease. This finding in isolation is of limited significance and should be interpreted with caution. Studies investigating the molecular profile of the disease show that in at least a subset of cases the disease is a clonal process. The classification of Rosai-Dorfman disease is therefore likely to change as our understanding of the aetiopathogenesis evolves.

Kaposi Sarcoma With Intravascular Primary Effusion Lymphoma in the Skin: A Potential Pitfall in HHV8 Immunohistochemistry Interpretation.

Primary effusion lymphoma is a rare, clinically aggressive large B-cell neoplasm universally associated with human herpesvirus 8 that occurs in the setting of immune compromise. It is classically described as a lymphomatous effusion occurring within body cavities. Recently, however, solid tumor masses, and rarely an intravascular form, have been described. We report a case of a cutaneous intravascular primary effusion lymphoma occurring within ectatic vascular spaces of a Kaposi sarcoma skin lesion in a human immunodeficiency virus-positive adult. Human herpesvirus 8 immunohistochemistry was positive in the nuclei of the Kaposi sarcoma spindled cells as well as within large intravascular plasmacytoid cells. This unusual case highlights the importance of careful assessment of the nature of human herpesvirus 8-positive staining cells in an otherwise typical Kaposi sarcoma. A careful search for dual pathology in immune-compromised patients as well as the importance of histologic assessment of skin lesions in human immunodeficiency virus-positive patients is also highlighted.