The mRNA encoding the calcium-binding protein psoriasin was identified as being more highly expressed in the in situ versus the invasive component of the same breast tumor. Reverse transcription-PCR analysis of total RNA extracted from three independent cases of ductal carcinoma in situ of the comedo type and three cases of high-grade invasive ductal carcinoma revealed a detectable level of psoriasin mRNA expression in the in situ lesions only. Similar analysis performed on total RNA extracted from frozen sections of 32 independent breast samples, representing a continuum from normal to invasive tumor, confirmed high psoriasin expression in ductal carcinoma in situ of the comedo type only. The possible functional role of the psoriasin protein in breast tumor cells remains to be determined.

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This work was supported by grants from the Canadian Breast Cancer Research Initiative and the U.S. Army Medical Research and Material Command. P. H. W. is a Medical Research Council of Canada Clinician-Scientist, L. C. M. is a Medical Research Council Scientist, and E. L. is a recipient of a U.S. Army Medical Research and Material Command Postdoctoral Fellowship.

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