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

The gene for bcl-2 is located on chromosome 18. The gene product is an 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. 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 85% of follicular lymphomas and 20% of diffuse large B cell lymphomas as a result of the t(14:18) translocation. It is also expressed in lymphoma which lack this translocation. 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:

	bcl-2 positivity
solitary fibrous tumours	95%
synovial sarcoma	93% (141/151)
leiomyoma	6/242,5
epithelioid leiomyoma	4/42
leiomyosarcoma	20% (17/86)5
rhabdomyosarcoma	7/72
neurofibroma	12/155
schwannoma	31/325
malignant peripheral nerve sheath tumours	16/465
haemangiopericytoma	19/245
spindle cell lipoma	16/185
fibromatosis	0/235
dermatofibroma	0/105
dermatofibrosarcoma protuberans	22/385
DFSP with fibrosarcomatous transformation	9/105
malignant fibrous histiocytoma	32/995
low grade myxofibrosarcoma	7/105
Kaposi's sarcoma	56/615
fibrosarcoma	9/435
fibroadenoma and phyllodes tumour of the breast	some stromal cells positive6
pseudoangiomatous hyperplasia of the breast	strongly positive (5/5)6
invasive carcinoma of breast	68% (97/142)8
nasopharyngeal carcinoma	89% (50/56)9
squamous cell carcinoma of lung	17/2513
adenocarcinoma of lung	15/4613
adenosquamous carcinoma of lung	1/313
large cell carcinoma of lung	6/1113
gastric carcinoma	36/8011
cholangiocarcinoma	0/2810

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.

	bcl-2
follicular hyperplasia	0/40 (only a few cells in the germinal centres were positive)15
follicular lymphoma	36/37 (positivity is independent of the grade of the lymphoma)15

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

• 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:

	n	MIB1	bcl-2	p16
cervical glandular intraepithelial neoplasia	21	86% of cases stained >10% of cells	negative or focal	all strong diffuse positivity
tubo-endometrial metaplasia	13	negative to <10% of cells	12/13 diffusely positive	62% focally positive
microglandular hyperplasia	14	negative to <10% of cells	negative (note reserve cells positive)	all negative

• Is is NOT of value in differentiating reactive marginal zone B-cell proliferations from marginal zone lymphoma¹⁶.

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):31^A.

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

©SMUHT/PW Bishop