Aim To analyse the clinicopathological features of sporadic Burkitt lymphoma (sBL).
Methods In a review of 1682 cases of non-Hodgkin lymphoma diagnosed in the First Affiliated Hospital and Zhongshan School of Medicine, from 1998 to 2010, 20 cases (1.2%) of sBL were identified. Histopathological examination, immunohistochemistry and in situ hybridisation were used to analyse the clinicopathological features of these cases.
Results Of the 20 cases of sBL, 18 patients were male and two were female. The mean age was 18 years (range 2–67 years). Extranodal presentation was more common than nodal presentation (55% vs 15%). Histopathologically, 18 cases (90%) showed monotonous medium-sized tumour cells, and two cases showed cells that were slightly pleomorphic in nuclear size and shape. Immunophenotypically, MUM1 was positive in three of 17 cases (17.6%). EBER expression was shown in five of 17 cases (29.4%), and all EBER-positive sBLs were Bcl-6+/MUM1−.
Conclusion sBL is rare and mainly affects male children, with predominantly extranodal presentation. MUM1 expression was found in some sBLs. EBER expression was found in 29.4% of sBLs from southern China, an area with a well-known high incidence of nasopharyngeal carcinoma, which is closely associated with Epstein–Barr virus infection.
- Burkitt lymphoma
- Epstein–Barr virus
- clinicopathological features
- southern China
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Burkitt lymphoma (BL) is a highly aggressive non-Hodgkin lymphoma (NHL) and is subdivided into three different categories based on epidemiological observations: endemic BL (eBL), sporadic BL (sBL), and immunodeficiency-associated BL. eBL occurs primarily in children 4–7 years in equatorial Africa and Papua New Guinea, and has a 95% association with Epstein–Barr virus (EBV) infection. sBL commonly arises in the gut and upper respiratory tract, and has a 30% association with EBV infection. Immunodeficiency-associated BL characteristically involves the lymph nodes and bone marrow and has a 30–40% association with EBV infection.1–3 However, few studies on clinicopathological features of sBL in southern China have been reported. We conducted a retrospective analysis to investigate the clinicopathological features, immunophenotype and EBV infection status of sBL in Guangzhou, southern China, in the last 12 years.
Materials and methods
Tissue samples and clinical evaluation
By reviewing 1682 cases of NHL diagnosed in our institution between January 1998 and March 2010, we found 20 consecutive cases of sBL. All patients were from local area of Guangzhou, southern China, and none had received chemotherapy or radiotherapy before biopsy. The histopathology of the disease was determined according to the criteria of WHO Classification (2008).4 None of the patients had a history of HIV infection, organ transplant or immunosuppressive status.
As previously described5, immunohistochemistry (IHC) staining was carried out on formalin-fixed, paraffin-embedded tissue using an EnVison Kit (Dako, Carpinteria, California, USA). The primary antibodies included LCA, CD20, CD79a, CD3, CD45RO, CD10, Bcl-6, Bcl-2, Ki-67, MUM1, TdT and c-Myc. For Ki-67 expression, 500 tumour cells were counted for each case under high power (×400), and the mean number of positive cells per 100 cells was considered to be the Ki-67-positive rate. Appropriate positive and negative control slides were employed.
In situ hybridisation
As previously described5, a positive result for EBER by in situ hybridisation was shown by a dark brown colour in the nuclei of cells. An EBER-positive nasopharyngeal carcinoma specimen was used as positive control. Tris-buffered saline (1 mol/l) was used instead of the EBER probe as the negative control in each run.
All statistical analyses were performed using SPSS 13.0 statistical software (SPSS, Chicago, Illinois, USA). A level of p<0.05 was set to be statistically significant.
Among 1682 cases of NHL diagnosed in our institution in the last 12 years, we found 20 cases (1.2%) of sBL; eighteen were male patients and two were female patients, and the ratio of male patients to female patients was 9:1. The mean age was 18 years, ranging from 2 to 67 years, with median age of 11 years. Twelve patients (60%) were children of 16 years or younger, and eight (40%) were adult. Primary extranodal diseases were seen in 11 cases (55%), and primary nodal diseases were seen in three cases (15%). Six cases (30%) presented nodal and extranodal involvement, without adequate information to identify the primary site. Extranodal involvement of sBL occurred in the following sites: gastrointestinal tract (n=5), abdominal cavity (n=3), head and neck (n=2), retroperitoneum (n=2), pelvis (n=2), brain (n=1), thoracic carvity (n=1) and kidney (n=1). Nodal involvement occurred in cervical lymph nodes (n=8), inguinal lymph nodes (n=3) and mesenteric lymph nodes (n=3). Staging information was available for 14 cases. Five patients were in stages I and II, and nine were in stages III and IV. Eleven patients received chemotherapy, and two received combined chemotherapy and surgical excision. Follow-up was available for 12 patients. Ten patients were alive without evidence of disease at 5 and 68 months. One patient died of multiple organ dysfunction syndrome at 2 months after diagnosis, and the other died of acute renal failure. The clinicopathological features of the 20 cases of sBL are given in table 1 and table 2.
Histopathologically, 19 cases of sBL showed a diffuse growth pattern, and one case showed a complex growth pattern including nodular, diffuse and tumour cells surrounding the remnant germinal centre. Eighteen cases (90%) exhibited a ‘starry-sky’ pattern: monotonous medium-sized tumour cells with round nuclei and a few small nucleoli (figure 1A). Neoplastic cells with slight pleomorphism in nuclear size and shape were seen in two cases. Numerous mitotic figures and apoptosis were found in all cases. Massive necrosis was found in two cases.
Tumour cells were positive for CD79a, CD10 and c-Myc (figure 1B), and negative for CD3 and TdT, in all cases of sBL. CD20 expression was shown in all but one case. One case was positive for CD20, CD79a and CD45RO, but negative for CD3. Expression of Bcl-6 was found in all but two cases (90%, 18/20). Bcl-2 expression was negative in all cases. Weak MUM1 expression was found in three cases (17.6%, 3/17). MUM1-positive cells ranged from 30% to 90% of tumour cells (figure 1C). A high proliferation index (>90% tumour cells labelled by Ki-67) was shown in all cases (table 2). The expression pattern of Bcl-6/MUM1 included: Bcl-6+/MUM1− in 12 cases (70.6%, 12/17), Bcl-6+/MUM1+ in three cases (17.6%, 3/17), and Bcl-6-/MUM1− in two cases (11.8%, 2/17).
EBER expression detected by in situ hybridisation
EBER expression was found in five cases (29.4%, 5/17) (figure 1D). All EBER-positive cases were Bcl-6+/MUM1−. Of 12 EBER-negative cases, seven were Bcl-6+/MUM1−, three were Bcl-6+/MUM1+, and two were Bcl-6-/MUM1−; however, the difference was not significant (p=0.522).
sBL is more common in children than adults, with a ratio of 1.5:1 in our series. Children had more extranodal disease than nodal disease (81% vs 59%), whereas adults had more nodal disease than extranodal disease (89% vs 53%).6 The expression of chemokines, chemokine receptors, adhesion molecules and proteases involving in cellular motility may contribute to tumour location.7
Histopathologically, a diffuse growth pattern was predominant. Vague nodules have been reported but they are extremely rare.8 In our series, only one case presented a complicated growth pattern, including nodular, diffuse and tumour cells surrounding the remnant germinal center. Two cases showed slight pleomorphism in nuclear size and shape. Dave et al9 verified eight cases of BL with a morphological diagnosis of diffuse large B-cell lymphoma using gene-expression profile analysis, suggesting that BL had a wide morphological spectrum.
Immunophenotypically, MUM1 was positive in three cases (17.6%, 3/17). The MUM1/IRF4 gene encodes a transcription factor thought to play a key role in lymphoid development. Expression of MUM1 in BL has been reported rarely. Carbone et al10 found two cases of BL with MUM1+ in occasional cells. Chuang et al11 reported MUM1 expression in five (17.8%) of 28 cases of BL in Taiwanese people. However, Gualco et al8 reported MUM1 expression in 41% (91/222) of BL cases from Brazil. In the present study, the expression pattern of Bcl-6/MUM1, including Bcl-6+/MUM1−, Bcl-6-/MUM1+ and Bcl-6-/MUM1−, was found in 72.2%, 16.7% and 10.5% of sBL cases, respectively.
EBV infection has been associated with BL at different frequencies, depending on the clinical variant and geographical region. In our series, EBER expression was detected in 29.4% (5/17) of sBL cases. Recently Bellan et al12 have revealed two distinct cells of origin for EBV-positive and EBV-negative BLs. EBV-positive BLs, mostly eBLs and AIDS-related BLs, showed high mutation rates and signs of antigen selection, suggesting that they might originate from late germinal centre B cells. In contrast, EBV-negative BLs, mostly sBLs, had a lower frequency of mutation rate and no signs of antigen selection, suggesting that they might originate from early centroblasts.
sBL is rare and mainly affects male children with predominantly extranodal presentation. MUM1 expression was found in some sBLs. EBER expression was found in 29.4% of sBL from Guangzhou, southern China.
Z Ye and Y Xiao contributed equally to this work.
Competing interests None declared.
Ethics approval Ethics approval was obtained.
Provenance and peer review Not commissioned; externally peer reviewed.