Purpose: The loss of expression of NES1, a novel putative tumor suppressor gene, is an early marker of breast tumorigenesis. NES1 is expressed in normal breast tissue and ductal hyperplasia but is absent or markedly diminished in invasive cancer. In cases of ductal carcinoma in situ (DCIS), NES1 expression has been shown previously to be present in approximately 50% of specimens. This study examined the expression level of NES1 in diagnostic biopsy samples found to contain pure DCIS. These data were then correlated with the pathologic findings found at definitive local surgery.
Methods and materials: Twenty-nine cases with initial biopsy showing DCIS without invasive carcinoma followed by subsequent reexcision were discovered and archived. Formalin-fixed tissue specimens were obtained for analysis. Each biopsy specimen was subjected to hematoxylin-eosin staining and reviewed by two pathologists to confirm the diagnosis of pure DCIS. NES1 cDNA (1069 bp), including 238 bp of 5' and 3' untranslated region and the entire protein-coding region, was cloned into a vector. To generate the antisense and sense RNA probes, the plasmid was linearized and the transcription reaction was carried out with polymerases T7 and T3, respectively. The detection of in situ hybridization probes was performed using an mRNAlocator-Biotin Kit. Staining was characterized as negative (0/1+) or positive (2+/3+). Subsequent to an initial biopsy diagnosis of DCIS, all cases had a definitive surgical procedure. Detailed sectioning of the resultant tissue was performed and subjected to hematoxylin-eosin staining to determine the presence or absence of invasive carcinoma.
Results: The initial diagnostic biopsy specimens showed that 17 of 17 high-grade, 3 of 7 intermediate-grade, and 3 of 5 low-grade DCIS specimens were negative for NES1 expression. Of the 6 cases of DCIS found to be positive for NES1 expression, none (0%) were subsequently found to have invasive carcinoma at definitive surgery. In contrast, the loss of NES1 expression in the initial diagnostic biopsy was associated with a 40% incidence of invasive carcinoma at definitive surgery. Additional stratification by nuclear grade showed invasive carcinoma in 5 (83%) of 6 NES1-negative, low- to intermediate-grade DCIS (p </=0.01) and 4 (24%) of 17 NES1-negative, high-grade DCIS (p </=0.05).
Conclusion: These results show that a lack of NES1 expression in DCIS identified at the diagnostic biopsy predicts for a high risk of invasive cancer in the definitive surgical specimen. The predictive value of NES1 expression appears to be particularly relevant for low- and intermediate-grade DCIS.