bcl-2, B-cell leukemia/lymphoma 2 gene

The gene for bcl-2 is located on chromosome 18. The gene product is a25 kDa inner mitochondrial membrane protein which inhibits apoptosis, so extending cell survivial. The bcl-2 gene is transcribed into three mRNA variants, which translate to give two proteins: bcl-2 alpha consists of 239 amino acids while bcl-2 beta of 205 amino acid is identical except for the C-terminal17. In follicular lymphomas, most t(14;18) translocation breakpoints cluster within a narrow region of a 5.4 kb exon that contains an untranslated region of the bcl-2 mRNA. The t(14;18) translocation results in a hybrid bcl-2/immunoglobulin heavy chain transcript consisting of the 5' half of the bcl-2 mRNA fused to a "decapitated" immunoglobulin heavy chain mRNA. Nucleotide sequence analyses confirmed that the hybrid transcripts continue to encode a normal bcl-2 protein18.

Immunohistochemical expression

• bcl-2 is normally expressed by small B lymphocytes of the mantle and marginal zones16 and by many T cells19.

• bcl-2 is over-expressed in follicular lymphomas with the translocation t(14;18)(q32;q21).  It is detected in 70-95% of follicular lymphomas20,21,22 and 20% of diffuse large B cell lymphomas22 as a result of the t(14:18) translocation. It is also expressed in lymphomas which lack this translocation. Expression is greater in grade I and lower in grade III follicular lymphomas. Microwave antigen retrieval appears to enhance immunoreactivity15.

• It is expressed in the thymus, by many cells in the medulla but only weakly in the cortex.

• There is strong staining of normal breast epithelium and a few cells stain in the perilobular stroma of the normal breast6. It is commonly positive in breast carcinoma, especially those tumours which occur in older patients8, are of low grade8, small size8 or oestrogen-receptor8 or progesterone-receptor8 positive. There is a tendency for expression to diminish with tumour progression8. Tamoxifen may reduce expression7. Apocrine ductal carcinoma in situ is usually negative (1/35 cases positive)12. Usefully in differentiation, it is rarely positive in lung or gastrointestinal tumours.

Soft tissue tumours:

Diagnostic utility

• Distinction of follicular lymphoma from follicular hyperplasia.  85% of follicular lymphomas are positive, with cytoplasmic staining.   Reactive follicles show staining of only scattered T cells within the germinal centres: a CD3 stain may be needed to assess the number of T-cells.

• Identification of marrow involvement in patients known to have a follicular lymphoma.

• Positivity for bcl-2 in a lymphoma is NOT evidence of follicular derivation.

• For distinguishing reactive monocytoid B-cell hyperplasia from marginal zone lymphoma23. It is NOT of value in differentiating reactive marginal zone B-cell proliferations from marginal zone lymphoma16.

• Differentiation of Burkitt lymphoma from diffuse large B-cell lymphoma: positivity for p53 and CD10 with negativity for bcl-2 and a high proliferation index favours Burkitt lymphoma24.

• Differentiation of primary breast carcinoma (commonly positive) from pulmonary and gastrointestinal primary carcinomas (rarely positive and if so only weakly and focally)4.

• bcl-2 expression is associated with a better prognosis in many carcinomas.  There is an inverse relationship with overexpression of p53.

• bcl-2 stains most basal cell carcinoma in a diffuse pattern, whereas trichoepitheliomas showed staining of the outermost epithelial layer.3

• Cervical intra-epithelial neoplasia.  The grade of CIN correlates with the proportion of cells that are bcl-2 positive.

• bcl-2 may be useful in conjunction with MIB1 and p16 in differentiating cervical glandular neoplasia, tuboendometrial metaplasia and microglandular hyperplasia14:

References

1 Hirakawa N, Naka T, Yamamoto I, Fukada T, Tsuneyoshi M. Overexpression of bcl-2 protein in synovial sarcomas.   Human Pathology 1996; 27: 1060-1065

2 Soini Y, Paakko P bcl-2 is preferentially expressed in tumours of muscle origin but is not related to p53 expression.   Histopathology 1996; 28:141-145.

3 Poniecka, A. W., Alexis, J. B. An immunohistochemical study of basal cell carcinoma and trichoepithelioma. Am J Dermatopathol 1999; 21:332-6

4 Battifora H. Immunohistochemistry in tumour prognosis. In Immunohistochemistry Long Course, Nice, October 18-23, 1998.

5 Ordonez NG. Localized (solitary) fibrous tumor of the pleura. Adv Anat Pathol 2000;7:327-340.

6 T Moore and AHS Lee. Expression of CD34 and bcl-2 in phyllodes tumours, fibroadenomas and spindle cell lesion of the breast. Histopathology 2001; 38-62-67.

7 Verghese et al. Mitotic rate, ER and bcl-2 expression in short term Tamoxifen treated breast cancer. J Pathol 2001:193(suppl):31A.

8 Nakopoulou, L., Michalopoulou, A., Giannopoulou, I., Tzonou, A., Keramopoulos, A., Lazaris, A. C., Davaris, P. bcl-2 protein expression is associated with a prognostically favourable phenotype in breast cancer irrespective of p53 immunostaining. Histopathology 1999;34:310-319.

9 Murono, S., Yoshizaki, T., Park, C. S., Furukawa, M. Association of Epstein-Barr virus infection with p53 protein accumulation but not bcl-2 protein in nasopharyngeal carcinoma. Histopathology 1999;34:432-8.

10 Arora, D. S., Ramsdale, J., Lodge, J. P., Wyatt, J. I. p53 but not bcl-2 is expressed by most cholangiocarcinomas: a study of 28 casesHistopathology 1999;34:497-501.

11 Kume, T., Oshima, K., Shinohara, T., Takeo, H., Yamashita, Y., Shirakusa, T., Kikuchi, M. Low rate of apoptosis and overexpression of bcl-2 in Epstein-Barr virus- associated gastric carcinoma Histopathology 1999;34:502-509.

12 Leal, C., Henrique, R., Monteiro, P., Lopes, C., Bento, M. J., De Sousa, C. P., Lopes, P., Olson, S., Silva, M. D., Page, D. L. Apocrine ductal carcinoma in situ of the breast: histologic classification and expression of biologic markers. Human Pathol 2001;32:487-493.

13 Han, H., Landreneau, R. J., Santucci, T. S., Tung, M. Y., Macherey, R. S., Shackney, S. E., Sturgis, C. D., Raab., S. S., Silverman, J. F. Prognostic value of immunohistochemical expressions of p53, HER-2/neu, and bcl-2 in stage I non-small-cell lung cancer. Human Pathol 2002;3:105-110.

14 Cameron RI, Maxwell R, Jenkins D, McCluggage WG. Immunohistochemical staining with MIB1, bcl-2 and p16 assists in the distinction of cervical glandular neoplasia from benign mimics. Pathological Society, July 2002, abstract no 67.

15 Cooper K, Hafajee Z. bcl-2 immunohistochemistry distinguishes follicular lymphoma from follicular hyperplasia in formalin-fixed tissue with microwave antigen retrieval. J Cellular Pathol 1996;1:52-56.

16 Meda, B. A., M. Frost, et al. (2003). "BCL-2 is consistently expressed in hyperplastic marginal zones of the spleen, abdominal lymph nodes, and ileal lymphoid tissue." Am J Surg Pathol 27(7): 888-94.

17 Tsujimoto Y,Croce CM Analysis of the structure, transcripts, and protein products of bcl-2, the gene involved in human follicular lymphoma. Proc Natl Acad Sci U S A 1986; 83:5214-8

18 Cleary ML, Smith SD,Sklar J. Cloning and structural analysis of cDNAs for bcl-2 and a hybrid bcl-2/immunoglobulin transcript resulting from the t(14;18) translocation. Cell 1986; 47:19-28

19 Pezzella F, Tse AG, Cordell JL, et al. Expression of the bcl-2 oncogene protein is not specific for the 14;18 chromosomal translocation. Am J Pathol 1990; 137:225-32

20 Horsman DE, Gascoyne RD, Coupland RW, et al. Comparison of cytogenetic analysis, southern analysis, and polymerase chain reaction for the detection of t(14; 18) in follicular lymphoma. Am J Clin Pathol 1995; 103:472-8

21 Pezzella F, Ralfkiaer E, Gatter KC, et al. The 14;18 translocation in European cases of follicular lymphoma: comparison of Southern blotting and the polymerase chain reaction. Br J Haematol 1990; 76:58-64

22 Weiss LM, Warnke RA, Sklar J, et al. Molecular analysis of the t(14;18) chromosomal translocation in malignant lymphomas. N Engl J Med 1987; 317:1185-9

23 Lai R, Arber DA, Chang KL, et al. Frequency of bcl-2 expression in non-Hodgkin's lymphoma: a study of 778 cases with comparison of marginal zone lymphoma and monocytoid B-cell hyperplasia. Mod Pathol 1998; 11:864-9

24 Braziel RM, Arber DA, Slovak ML, et al. The Burkitt-like lymphomas: a Southwest Oncology Group study delineating phenotypic, genotypic, and clinical features. Blood 2001; 97:3713-20 FULL TEXT

©SMUHT/PW Bishop