INTRODUCTION along with the T cell markers (CD2,

INTRODUCTIONLymphnode sarcomas are very uncommon tumours arising either from Interdigitatingdendritic cells present in the paracortical region or from Follicular dendriticcells present in follicles and rarely from fibroblastic reticular cells ensheathingpost capillary venules in lymphnodes. Interdigitating dendritic cells arisefrom hematopoietic stem cell expressing high levels of MHC II and are stronglyS100 positive.  Follicular dendriticcells arise from mesenchymal stem cells and are present in the follicles in thelymph node. They present antigen to B lymphocytes and are positive for CD 21,CD23 and CD35 but negative for CD45.

Fibroblastic reticular cells are also mesenchymalin origin and are involved in transport of cytokines and other mediators.3Only nineteen cases have been reported till now thus the case is beingreported because of its rarity.Case Report                     37-year-oldfemale presented with mass in left axilla in the Surgery OPD of a tertiary carecenter.

Breast examination did not show any lump. On ultrasonomammography bothbreasts were normal. Multiple enlarged hypoechoic lymph nodes measuring 40X20mmin left axillary region were present.  FNAC fromoutside reported the presence of atypical suspicious cells. So excision biopsy forthe same was done for histopathological evaluation.Grossly, a nodular grey white and firm tissuepiece measuring 4 X 2 cm in size was received and tissue sections wereprocessed.

Histopathological examination showed round to oval cells withvesicular nuclei having prominent nucleoli along with mature lymphocytes interspersedamongst which were seen elongated tumour cells with moderate amount ofeosinophilic cytoplasm forming fascicles and sheets.Histopathologically a diagnosis ofLymphoproliferative disorder- Non-Hodgkin’s Lymphoma was made and IHC wasadvised.Immunohistochemistry was done first using CD45 (leucocyte commonantigen) which showed positive staining for lymphocytes only whereas the otherpopulation of cells were negative. After this the B cell markers (CD20 andPAX5)were used to rule out B cell lymphomas along with the T cell markers (CD2, CD3,CD4 and CD8) to rule out Tcell lymphomas. All of these markers showed negativeresults. CD56 and CD57 were also negative and thus, ruled out neuroendocrinetumours.

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Further, CD1a, CD34 and desmin negativity ruled out Langerhans cellhistiocytosis, Langerhans cell sarcoma, angiosarcomas and rhabdomyosarcoma. MPOstain, CD 15 and CD 30 negativity ruled out the myeloid origin as well ashodgkins and anaplastic large cell lymphoma.As CD1a was negative with focal CD68 positivity possibility ofInterdigitating dendritic cell sarcoma was ruled out. Then Follicular dendriticcell markers were used. CD21, the most sensitive marker for FDCs, came outnegative but pancytokeratin showed very strong positivity, proving epithelialorigin of neoplastic cells. CK8 and CK18 were also positive. Smooth muscleactin (SMA)showed focal positivity thus showing fibroblastic nature of thetumour.

So it was diagnosed as Fibroblastic reticulum cell sarcoma.Thesefindings suggested that CIRCs originate from mesenchymal stem cells that showbi-directional differentiation towards epithelioid and myoid/myofibroblasticcells. 3DISCUSSIONLymph node consists of heterogenous populationof stromal cells showing reticular morphology and this group is formed byfollicular dendritic cells (FDCs), interdigitating dendritic cells (IDCs),Langerhan’s cells (LCs), and fibroblastic reticular cells (FRCs).

FRCs plays arole in maintaining the integrity of lymph nodes, production and transport ofcytokines and other mediators.Franke and Moll in the year 1987 were thefirst to identify and label these cells as Cytokeratin-positive interstitialreticulum cells.2These interstitial reticulum cells are consideredto be indigenous to lymphoid organs, originating from mesenchymal stem cells.They have long slender cytoplasmic processes extending between lymphocytes andare found in the extrafollicular compartment, paracortex and medulla of lymphnodes, spleen and tonsils.

They express cytokeratin 8 and 18 with some ofthem co-expressing smooth muscle actin (SMA) (20-60%) and desmin(1-10%).Dendritic cell markers are negative. Lymph node sarcomas are very uncommon tumours. Arising either fromInterdigitating dendritic cells present in the paracortical region or fromFollicular dendritic cells present in follicles and rarest from fibroblasticreticular cells ensheathing post capillary venules in lymphnodes.

Interdigitatingdendritic cells arise from hematopoietic stem cell expressing high levels ofMHC II and are strongly S100 positive. Whereas Follicular dendritic cells arisefrom mesenchymal stem cells and arepresent in the follicles in the lymph node.They present antigen to B lymphocytes and are positive for CD 21, CD23 and CD35but negative for CD45. Fibroblastic reticular cells are also mesenchymal inorigin and are involved in transport of cytokines and other mediators.3IDC sarcomas typically have branching and interdigitatingprocesses with an absence of cell junctions.4,5 FDC sarcomas arecharacterized by interdigitating spindle cells with well-developed desmosomesand a lack of cytoplasmic filaments.6,7,8 On the other hand thekeratin-positive subset of FRC sarcoma can apparently show both desmosomes andtonofilaments  along with variablemyofibroblastic features and dense bodies.9Immunophenotypically FDC sarcomas have shown strong uniformpositivity for CD21, CD23 and CD35 in nearly all reported cases.6,7Some investigators have reported expression of CD45 (weak), B cell markersCD19, CD20, CD22, EMA or CD4 on cases of FDC sarcoma.Nodal FRC show uniform positivity for vimentin with subsetspositive for actin, desmin, CD68 and keratin with focal SMA positivity.10