BRCA1 and PARP1 mRNA expression during progression from normal breast to ductal carcinoma in situ and invasive breast cancer: a laser microdissection study

The contribution of DNA damage repair mechanisms to the progression of normal breast to ductal carcinoma in situ (DCIS) and invasive ductal carcinoma is largely unknown. The purpose of this report was to assess the mRNA expression levels of two important genes associated with DNA repair, BRCA1 and PARP1, in normal breast tissue, DCIS G1, G2 and G3, and co-existing adjacent invasive ductal carcinoma. BRCA1 and PARP1 mRNA expression was assessed in 32 ductal carcinomas in situ of the breast using a laser microdissection and pressure catapulting system and quantitative real-time PCR. The relative expression of BRCA1 mRNA was significantly increased in DCIS G2 and DCIS G3 relative to normal breast tissue (p = 0.02, p = 0.001, respectively). Significant differences in BRCA1 expression were observed between DCIS G1 and G2 (p = 0.02) and between DCIS G1 and G3 (p = 0.0007). No significant differences in BRCA1 expression were observed between normal breast tissue and DCIS G1 and between DCIS component and adjacent invasive ductal carcinoma. No significant differences in the relative expression of PARP1 mRNA were observed between groups. Increased BRCA1 mRNA expression (but not PARP1 mRNA) occurs early in the development of breast cancer, i.e. at the noninvasive (DCIS) stage, suggesting a demand for increased activity of a DNA double-strand break repair by homologous recombination. DCIS G1 and normal breast tissue share highly similar BRCA1 and PARP1 expression level. This finding supports the idea that DCIS G1 belongs to a separate family of precursor lesions with low malignant potential.