Angioimmunoblastic T-cell lymphoma (AITL) is one of the most common subtypes of peripheral T-cell lymphomas, accounting for approximately 15-20% of all cases, or 1-2% of all non-Hodgkin lymphomas [1]. AITL is frequently accompanied by a polymorphic nature including fever, skin eruptions, polyclonal hypergammaglobulinemia, generalized lymphadenopathy and hepatosplenomegaly [2]. Histopathologically, the primary site of AITL is lymph node characterized by the effacement of the lymph node architecture, the increase of arborizing high endothelial venules and the infiltration of clear small- to medium-sized lymphocytes, along with the increase of B-immunoblasts that usually contain Epstein-Barr virus (EBV). AITL patients exhibit immunodeficiency secondary to the neoplastic process. Expansion of EBV-positive B cell is thought to be a consequence of underlying immune dysfunction [3]. In rare condition, secondary EBV-associated B cell lymphoma may occur together with AITL. However, to our knowledge, so far only 22 cases of AITL developed EBV-associated secondary B cell lymphomas have been described in English literature [4–14]. Herein, we report a case of secondary EBV-associated diffuse large B cell lymphoma occurring in the skin of a patient with lymph node AITL.

A 65-year-old Chinese male patient presented with a 6-month history of enlarged right inguinal lymph nodes without pain and fever and initially sought examination and treatment at our hospital in September, 2009. Physical examination revealed multiple enlarged lymph nodes easily identified in the right inguinal region, and the spleen was palpable 2 cm below the left costal margin without discrete masses or tenderness. Maculopapular eruptions could be found in the trunk. There was no remarkable edema and masses observed in the skin. The laboratory results including blood count, differential, liver and renal function were within the normal range. Eosinophilia and hypergammaglobulinemia were not observed. Computed tomography (CT) scan disclosed the enlargement of right inguinal and visceral lymph nodes, as well as hepatosplenomegaly. Test for EBV exhibited both viral capsid antigen (VCA) and EBV-associated antigen positive.

The patient then underwent biopsy of right inguinal lymph node, but the biopsy of skin lesion was not performed at that time. The biopsy tissue was routinely processed and stained by hematoxylin and eosin (H&E). Under the microscopy, the normal architecture of lymph node was destroyed by polymorphic cellular infiltration composed of diffused small to medium-sized lymphoid cells along with plasma cells and eosinophils. The infiltrated lymphocytes had clear cytoplasm with mildly irregular nuclei. Some of large immunoblast-like lymphoid cells with large distinct nuclei and clear cytoplasm were observed to intermingle with those infiltrated lymphocytes. Numerous arborizing high-endothelial venules were prominent in the background of lymph node. In addition, scattered Reed-Sternberg (RS)-like cells with irregular multilobated nuclei and large eosinophilic nucleoli were also present in the node (Figure 1A-B). Immunohistochemically, the infiltrated small to medium-sized lymphoid cells were strongly positive for CD3, CD45RO, CD10 and CD4, but negative for CD20, CD79a, PAX-5, CD56, MUM-1 and CD30. The large immunoblast-like cells and scattered RS-like cells showed immunoreactive for CD20, CD79a and CD30. The proliferation of follicular dendritic cells highlighted by CD21 and CD23 was prominent throughout node, and entrapped the high-endothelial venules. By in situ hybridization assay, EBER-positive signal was observed in either scattered large B immunoblasts or RS-like cells (Figure 1C-F). Based on clinical presentation and histological findings, a histological diagnosis of angioimmunoblastic T-cell lymphoma (AITL) was made according to the criteria of WHO classification [3].

After the diagnosis of AITL, the patient received 6 cycles of chemotherapy with CHOP regimen (cyclophosphamide, vincristine, adriamycin, and prednisone), but his symptoms did not disappear. The patient was followed up without any treatment for nearly one year after completing the whole chemotherapy courses. There was no further complaint from the patient during the follow-up period. In April, 2011, nineteen months after initial diagnosis the patient was readmitted to our hospital due to presentation of multiple plaques and nodules on the skin. Skin examination showed irregular plaques and nodules ranging from 0.5 to 2.5 cm in diameters in the trunk and extremities. CT scan revealed multiple enlargements of right inguinal and visceral lymph nodes as well as hepatosplenomegaly. Bone marrow aspiration was normal. The skin biopsies were performed in the skin lesion located at the left upper arm.

Microscopically, dermal and subcutaneous tissue was infiltrated by sheets of a monotonous population of medium- to large-sized atypical lymphoid cells without epidermotropism. Cellular atypia exhibited irregular nuclei, large nucleoli and vesicular chromatin with a brisk mitotic rate, atypical mitotic figures (Figure 2A-B). Immunohistochemically, the atypical cells were strongly positive for CD20, CD79a and Bcl-6, but negative for CD3, CD5, and CD45RO. EBV detection by in situ hybridization for EBERs showed diffuse positive reaction (Figure 2C-F). These findings were compatible with diffuse large B cell lymphoma (DLBCL). Sections of the lymph node biopsy performed one year earlier were reviewed. The structure and cytologic features of skin lesion were distinct from those of the lymph node. There was a diffuse infiltrate of predominantly small to medium-sized lymphocytes with unambiguous T cell markers by immunohistochemical analysis in lymph node. These tumor cells were negative reaction to EBER assay. However, the infiltrated large sized neoplastic cells in the skin lesion were identified as B lymphocytes and positive to EBER assay. Based on these findings, a histological diagnosis of AITL-developed secondary EBV-associated DLBCL of skin was made.

After diagnosis, the patient received a cycle of R-CHOP regimen (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) and achieved a partial response. However, pancytopenia and suppression of cellular immunity were observed. The patient refused further treatment of R-hyperCVAD regimen (rituximab, cyclophosphamide, vincristine, doxorubicin, and dexamethasone) and was discharged from hospital. The further following up was not performed due to contact loss of the patient.

Angioimmunoblastic T-cell lymphoma (AITL) was previously regarded to be an atypical reactive process. In 1974, Frizzera et al. firstly termed it as "angioimmunoblastic lymphadenopathy with dysproteinemia (AILD)" [15], of which AILD was described as a reactive lymphoproliferative disorder of T lymphocytes [16]. AITL was considered as a malignant transformation of AILD, but the histological distinguishing AITL from AILD was quite difficult. In the past, the presence of clusters of cells with abundant clear cytoplasm was regarded as one of the most important morphological criteria and used to distinguish AITL from AILD. However, subsequent molecular and cytogenetic studies revealed that clonal TCR gene rearrangement and chromosomal abnormalities were identified in the majority of AILD [17, 18], which indicated most cases previously diagnosed as AILD actually represented AITL. In 2001, WHO classification of tumor of hematopoietic and lymphoid tissue suggested AITL was most likely to arise as a peripheral T-cell lymphoma. As both terms of AITL and AILD were in common use, they could be used interchangeably in clinics. However, some researchers argued that a few cases of AILD with atypical or oligoclonal proliferation might precede the development of AITL, and should be classified as a distinct entity of preneoplastic process [19, 20]. Although debate remained, we considered AILD might represent the existence of stages in the development of AITL rather than independent disease entities.

Although the pathogenesis of AITL remains unclear, it is currently thought to most likely derived from germinal-center T-helper cells (T_FH) [21]. The primary site of AITL is lymph node and virtually all patients present with generalized lymphadenopathy. Histological examination of the lymph nodes exhibits nearly complete effacement of the follicular architecture, a mixed lymphoid infiltrate, and numerous high endothelial venules in an expanded T-cell zone. In some cases, the lymph nodes show diffuse obliteration of their architecture by lymphoid infiltration consisting of lymphocytes, immunoblasts, plasma cells, and histiocytes, together with numerous high endothelial venules surrounded by an expanded network of follicular dendritic cells. Immunohistochemically, the neoplastic cells express most pan T-cell antigens such as CD2, CD3 and CD5. The majority of the proliferating cells are CD4 positive or, less often, CD8 positive [3]. Attygalle et al. demonstrated that CD10 was a phenotypic marker, which specifically identified the tumor cells of 90% of AITL [22]. Dorfman et al. reported that programmed death-1 (PD-1), a member of the CD28 costimulatory receptor family, is expressed by germinal center-associated T cells in AITL [23]. De Leval et al. indicated tumor cells in AITL could overexpress CXCL13, which is the characteristic of normal T_FH cells [21]. These researchers suggest those immunophenotypes are helpful to distinguish AITL from atypical paracortical hyperplasia and other peripheral T-cell lymphomas as well as diagnosing extranodal dissemination. In our case, not only histological examination of lymph node demonstrated a morphological characteristic of AITL, but also the presence of T-cell linage with aberrant CD4 and CD10 expression identified in neoplastic cells by immunohistochemical staining which also strongly supported a diagnosis of AITL at initial lymph node biopsy.

The presence of large immunoblast cells and scattered RS-like cells in AITL might create diagnostic confusion with other neoplastic condition of lymphoid tissue. The main differential diagnoses include classical Hodgkin lymphoma (cHL) and T cell/histiocyte-rich large B-cell lymphoma (THRLBCL). THRLBCL is characterized by a limited number of scattered, large, atypical B cells embedded in a background of abundant T cells and frequently histiocytes. Immunohistochemically, large atypical cells express pan B-cell markers and no expression of CD30, and are lack of EBV infection. The background of THRLBCL is composed of variable number of CD68-positive histiocytes and CD3-, CD5-positive small T cells rather than CD4-, CD10- and CXCL13-positive small to medium-sized T_FH cells. Numerous high endothelial venules surrounded by an expanded network of follicular dendritic cells highlighted by CD21 and CD23 will be useful to distinguish AITL form THRLBCL. In this present case, an interesting finding was the presence of occasional CD30 and EBV-positive RS-like cells within inflammatory background of lymph node. This histological finding was similar to the morphological feature of cHL. However, recognition of cytologic atypia or immunophenotypic aberrancy in the background T cells is critical for making the differential diagnosis between AITL and cHL.

In conclusion, secondary B-cell lymphoma in AITL is rare. Herein we report the first case of cutaneous EBV-associated DLBCL sequential to AITL in Chinese patients. Extranodal involvement by secondary lymphoma in the patients with AITL might imply a poor prognosis. Therefore, clinicians should keep in mind that there is a possibility of sequential development of B-cell lymphoma after AITL. It is necessary to perform lymph node and skin biopsies regularly to detect the progression to secondary lymphomas for patients with AITL.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.