Cutress, R.I., Townsend, P.A., Bateman, A.C., Johnson, P.W., Ryder, K., Barnes, D.M. and Packham, G. (2001) BAG-1 immunostaining and survival in early breast cancer. Journal of Clinical Oncology, 19 (16), 3706-3707. (PMID:11504752)
Abstract
To the Editor: We read with interest the article by Turner et al1 in the February 15, 2001, issue describing the association between increased levels of cytosolic, but not nuclear, BAG-1 immunostaining and long-term survival in early breast cancer. There is, however, some difficulty in determining the precise relationship between BAG-1 expression and the biology of breast cancer. A previous report by this group using a monoclonal antibody described a significant positive correlation between high levels of nuclear BAG-1 immunostaining and overall survival, whereas a report from a different group described inferior survival in patients with high levels of nuclear BAG-1 staining using a polyclonal antibody.
From the examples of immunostaining presented in the two articles from Turner and co-workers, it seems that at least some of the same patients were included in the two series with discrepant results. It would be helpful to know the degree of overlap between the two cohorts and whether any potential selection bias may have influenced the results. In particular, the low proportion of estrogen receptor–positive cases (41% as against an expected level of 70%) suggests that the sample described may not be wholly representative of an early-stage breast cancer population. Tumor grade was not included in the table of patient characteristics, and as correlations have been found between tumor differentiation and BAG-1 status by at least one group, it would be instructive to know if BAG-1 was predictive of outcome independent of tumor grade.
It is also possible that the discrepant results relate to differences in methodology, such as antigen retrieval techniques, which were not described in the more recent article. It is clear that further work is required to properly describe the potential role of BAG-1 expression as a biologic variable, and it would be helpful to other investigators to have these critical details.
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