Inflammatory Pseudotumor-like Follicular Dendritic Cell Tumor (IPT-FDC)

The Key Features

  • Restricted in the liver and spleen;

  • Similar morphologic features to IMT;

  • FDC markers: expressed in most of cases but not required for diagnosis;

  • EBER-ISH positive in spindle cells.

Related Cases: HP-282

Clinical Futures

  • Female predilection, M:F=2.2:1, mean age 54.5 years;
  • Restricted to the liver and spleen;

  • The most common symptoms: abdominal discomfort or pain; systemic symptoms not common.

Gross Findings

  • Mostly solitary, large mass lesions, ranging in maximum dimension from 2 to 22 cm (average 9.2 cm);

  • Round to ovoid, well-circumscribed with pushing borders;

  • Tan cut surface with irregular patches of hemorrhage and yellowish necrotic areas; large lesions may have cystic changes.

Microscopic Findings

  • Well demarcated from the surrounding splenic parenchyma, with or without a fibrous capsule;

  • Closely resembles inflammatory pseudotumor with admixture of lymphocytes, plasma cells, and spindle cell proliferation;

  • The plasma cells and lymphocytes are reactive with no cytologic atypia or clonality. However, the lymphoplasmacytic component may be densely packed and mimics low-grade lymphoma. Eosinophils are often increased;

  • The spindle cells are scattered or form loose clusters, and are sometimes difficult to identify due to a background with abundant lymphocytes and plasma cells. They may proliferate in storiform, fascicular, or solid sheet pattern;

  • The spindle cells usually do not have significant cytologic atypia. The nuclei are ovoid or elongated with thin nuclear membrane, vesicular chromatin, and small central nucleoli. The cytoplasm is abundant and pale pink staining with no distinct cytoplasmic borders;

  • Occasional large atypical cells may be present with large nuclei, irregular nuclear membrane, coarsely condensed chromatin, and multiple, large eosinophilic nucleoli. The atypical cells may resemble Hodgkin lymphoma cells;

  • No increase in mitoses or atypical mitotic figures;

  • Some blood vessels show ectasia and deposition of abundant fibrinous material in the wall.

Subtypes

  • Granulomatous and Eosinophil-rich Variants [2]:

    • Cases with abundant coalescent non-caseating epithelioid granulomas, closely resembling sarcoidosis
    • Cases  with  marked increased in eosinophils and large necrotic eosinophilic abscesses
    • Negative for infectious process
    • May mimic classic Hodgkin lymphoma in cases with large atypical cells

Immunohistochemistry Staining

  • Usually positive for at least one of the FDC markers (CD21, CD23, CD35 CNA.42). But compared to the conventional FDC tumors, the staining could be patchy and focal;

  • Often positive for clusterin, CNA.42, CXCL13, D2-40 and SMA;

  • EBER-ISH diffusely positive in the spindle cells; background lymphocytes negative;

  • Negative for ALK1, desmin, caldesmon, CD1a, CD30, CD31, CD34, HMB45, and S100;

  • IgG4+ cells usually not increased; but cases with increased IgG4+ cells have been reported [3].

Differential Diagnosis

  • Conventional FDC tumor:

    • Mostly in extra-splenic or -hepatic locations;

    • Similar morphologic features with less infiltration of lymphoplasmacytic cells;

    • More often positive for FDC markers;

    • Negative for EBER-ISH;

    • Often recurs and metastasizes.

  • Conventional IPT or IMT:

    • Very similar morphology;

    • SMA usually diffusely positive, ALK positive in subset of cases;

    • Negative for EBER-ISH.

  • IgG4 disease:
    • Similar morphologic features;
    • Negative for EBER-ISH;
    • IPT-FDC usually has no increase in IgG4+ cells; but may have increased IgG4 in subset of cases [3].
  • Sclerosing angiomatoid nodular transformation (SANT) [4,5]:
    • Frequent nodular growth patter with a rich network of capillaries resembling granulation tissue;
    • Variable degree of fibrosis and macrophage collection;
    • May express FDC markers  in a subset of the cases;
    • Negative for EBER-ISH.

Treatment and Prognosis

  • Mostly indolent with a low rate of local recurrence or metastasis;

  • Surgical resection usually sufficient for localized diseases; reported splenic cases had no recurrence or metastasis, and hepatic cases showed a low recurrence or metastasis rate.

Reference

  1. Am J Surg Pathol 25(6): 721731, 2001

  2. Am J Surg Pathol 2014;38:646653

  3. Pathology International 2013; 63: 245251

  4. Histopathology 2008; 53: 299310

  5. Virchows Arch 2008; 453: 27582

  6. Int J Clin Exp Pathol 2014;7(5):2421-2429

Last update: 05/052015