Histiocytic Sarcoma



Histiocytic Sarcoma


Aaron Auerbach, MD, PhD





Key Facts


Terminology



  • Histiocytic sarcoma (HS)


  • Malignant histiocytosis


  • Extramedullary monocytic tumor


Clinical Issues



  • Extremely rare tumor


  • Mostly seen in adults


  • Usually rash or single lesion on skin


  • Some patients develop both histiocytic tumors and lymphoid tumors (transdifferentiation)


Microscopic Pathology



  • Dermal and subcutaneous infiltrate sparing epidermis


  • Composed of large, noncohesive, atypical epithelioid tumor cells with abundant cytoplasm


  • Immunohistochemistry: CD163(+), CD68(+), lysozyme(+), CD4 (+/−), S100(-)/focal(+)


  • B-cell markers, melanoma markers, carcinoma markers, and myeloid markers negative


Ancillary Tests



  • B- and T-cell gene rearrangements usually negative


Top Differential Diagnoses



  • Myeloid sarcoma


  • Langerhans cell histiocytosis and Langerhans cell sarcoma


  • Anaplastic large cell lymphoma (ALCL)


  • Diffuse large B-cell lymphoma


  • Classic Hodgkin lymphoma


  • Melanoma


  • Carcinoma







Histiocytic sarcoma at low magnification shows a diffuse, dermal-based sheet-like proliferation of enlarged, undifferentiated-appearing cells at this power.






High magnification of histiocytic sarcoma shows sheets of markedly enlarged and atypical cells image with abundant cytoplasm, enlarged nuclei with prominent nucleoli, and scattered mitotic figures image.


TERMINOLOGY


Abbreviations



  • Histiocytic sarcoma (HS)


Synonyms



  • Extramedullary monocytic tumor


  • Malignant histiocytosis


  • True histiocytic lymphoma


Definitions



  • Malignant tumor of mature histiocytes



    • Neoplasms associated with acute monocytic leukemia are excluded



      • Are now classified as monocytic sarcoma


ETIOLOGY/PATHOGENESIS


Etiology



  • Idiopathic



    • Sometimes associated with germ cell tumors


    • Also can be associated with lymphoma, leukemia, or myelodysplastic syndrome


Postulated Normal Counterpart



  • Mature histiocyte


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Extremely rare tumor


  • Age



    • Mostly in adults



      • Median age = 52 years old


      • Rare in children


  • Gender



    • Approximately equal male:female ratio


  • Ethnicity



    • No known ethnic predilection


Site



  • Most cases are extranodal



    • Skin, gastrointestinal tract, and soft tissue most common


  • Lymph node less common


Presentation



  • Often a single painless mass



    • B symptoms common


  • Skin



    • Variable presentation



      • Can be seen as a rash, a single lesion, or multiple lesions (disseminated)


  • Gastrointestinal tract



    • Abdominal pain


    • Intestinal obstruction


  • Bone marrow



    • Focal/patchy bone marrow involvement is considered HS



      • Diffuse bone marrow involvement is currently classified as acute monocytic leukemia


Laboratory Tests



  • Cytopenias in some patients



    • Thrombocytopenia is most common


Natural History



  • Some patients develop both histiocytic tumors and lymphoid tumors



    • Lineage promiscuity (a.k.a. transdifferentiation)


    • Both tumors share molecular findings



      • HS can have t(14;18)(q32;q21)


      • HS can have clonal IgH gene rearrangements


      • Identical IgH rearrangements or BCL2 gene breakpoints in same patients with HS and B-cell lymphoma


Treatment



  • Surgical approaches




    • Surgical excision with wide margins


  • Adjuvant therapy



    • Chemotherapy and radiation therapy



      • Non-Hodgkin lymphoma protocols (i.e., CHOP)


      • Acute leukemia protocols


Prognosis



  • Low-stage (localized) lesions may be less clinically aggressive


  • High-stage lesions (multiple lesions, systemic disease, recurrences) resistant to adjuvant therapy



    • 80% of patients die of disease


MACROSCOPIC FEATURES


General Features



  • Skin with rash or tumor nodule



    • 1 or more firm lesions


MICROSCOPIC PATHOLOGY


Histologic Features



  • Skin



    • Dermal and subcutaneous infiltrate with infiltrative borders


    • Spares epidermis, separated by grenz zone


  • Lymph node



    • Usually diffuse effacement of lymph node architecture


    • Focal involvement is often in paracortex


    • Rare tumor is seen in sinuses


  • Hemophagocytosis, sometimes



    • Emperipolesis in some cases


  • Mitotic figures


  • Inflammatory background



    • Often prominent



      • Reactive T cells, plasma cells, eosinophils


      • Especially in HS of central nervous system


Cytologic Features



  • Neoplastic cells, large and noncohesive



    • Nuclei



      • Usually epithelioid


      • Rarely spindle-shaped


      • Often highly pleomorphic cells, sometimes monomorphic


      • Vesicular chromatin


      • Nucleoli, prominent sometimes


      • Multinucleated cells can be seen


    • Cytoplasm is abundant



      • Eosinophilic


      • Cytoplasmic vacuoles sometimes


      • Xanthomatous appearance sometimes


ANCILLARY TESTS


Immunohistochemistry

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Histiocytic Sarcoma

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