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Correspondence |
University Vienna, Vienna, Austria
To the Editor-in-Chief:
We have read with interest the article of Liu et al1 on down-regulation of KAI1-metastasis suppressor protein in cervical cancer.1 This study confirms our results published previously.2 Unfortunately Liu et al1 missed one of our papers on KAI-1 expression in cervical carcinoma, wherein some of the problems discussed in their paper have already been addressed. Liu et al1 suggest that down-regulation of KAI1 might occur early in cervical carcinogenesis, but they did not include any precancerous lesions of the cervix in their study. In contrast, based on immunostaining of various stages of cervical dysplasia, we demonstrated that down-regulation of KAI in fact occurs at a very early stage of cervical carcinogenesis, while in 10 cases of cervical intraepithelial neoplasia (CIN) grade I, strong KAI1 expression was found in all cases, no difference in KAI1 expression in CIN II (n = 10) or CIN III (n = 10) and invasive carcinomas (n = 75) was found (P <0.05, Kruskal-Wallis test). Liu et al1 also hypothesize that KAI1 may not have a prognostic influence in cervical cancer, but were not able to perform survival analysis due to the short follow-up time of patients. In our collective of primary irradiated cervical cancers we have demonstrated that KAI1 down-regulation was indeed not associated with prognosis (P >0.05, log-rank test).
In our view, a technical problem of the real time-reverse transcriptase-polymerase chain reaction-based study of Liu et al1 is the fact that KAI1 is also strongly expressed in lymphocytes and macrophages,3 as stated by Liu and colleagues themselves.1 In cervical cancer, inflammatory stroma reaction is a common event, and is even very prominent in many cases.4 To us, mRNA- or protein-based methods for detection of KAI1 expression without reliable separation of tumor cells from the surrounding stroma (eg, by microdissection) bear a great risk, in that results may be drastically influenced by the overlap from a dense inflammatory infiltrate present in the samples. This problem is aggravated if lymph node metastases are investigated. Therefore, in our opinion, immunohistochemistry has to be considered as the most reliable method for detection of KAI1 down-regulation in tissue samples.
References
University of Virginia Health Sciences Center Charlottesville,Virginia
It is unfortunate that we accidentally missed more recent publication of Schindl et al1 on KAI1 expression in cervical carcinoma1 , yet we agree that immunohistochemistry is a reliable method for the detection of KAI1 expression in tumor tissues. Knowing that most KAI1 antibodies do not work well with frozen tissues and that analysis of RNA has been widely used in KAI1 expression study, we used both immunohistochemistry and real-time quantitative PCR to double check the expression of KAI1 at protein and at RNA levels, respectively.2
The strong expression of KAI1 in lymphocytes, stromal cells, and endothelial tissues is really a problem for KAI1 analysis of cervical tumors. In this study, to overcome the problem of contamination by the normal cells and tissues, we took two strategies to prepare the materials. First, we strictly selected samples from only patients with bulky tumor so that the whole sample consisted of tumor tissue. Second, in order to confirm that the specimens were enriched for tumor tissue, we examined a part of the samples histopathologically with hematoxylin and eosin stain. We thus could make sure that each specimen used for RNA extraction contained at least 80% tumor cells. We believe that with such restricted sample selection and scrupulous management, the RNA used for RT-PCR should be able to represent the tumor character. In fact, our results demonstrated that the expression of KAI1 was correlated well between immunohistochemical and real-time quantitative PCR methods. Therefore, with the real-time RT-PCR study, we believe we have further confirmed that the expression of KAI1 was down-regulated frequently in cervical cancer.
References
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