Expression of a cancer associated isoform of PCNA in breast cancer has implications as a potential biomarker

Abstract

21069 Background: We have identified a novel cancer associated isoform of the protein, proliferating cell nuclear antigen (PCNA), termed (caPCNA), and demonstrated that this isoform arises through a direct protein post-translational modification, and not via genetic mutation or RNA splice variation. Our results suggest that caPCNA has the potential to serve as a highly effective and unique marker for identifying malignant breast cancer cells. Methods: This assertion is based on our proteomic-based analyses of more than 60 malignant and non- malignant breast cell lines and tissues. Commercially available antibodies against PCNA cannot distinguish between the different isoforms of PCNA present in malignant and non-malignant breast cells and cannot be used clinically to differentiate between normal and malignant breast tissue. However, we have recently developed a rabbit polyclonal antibody, (caPCNAab), which specifically recognizes only the caPCNA isoform expressed by malignant human breast cells. Results: Using this antibody we clearly show that caPCNA is expressed only in malignant breast cells and tissues, and can be found in early disease. caPCNA expression in tissues was quantified as average staining intensity X average percentage of cells stained. Using this criterion the following data were obtained: 10 cases of normal breast tissue (reduction mammoplasty) gave a total score of 1%; 35 cases of normal breast tissue adjacent to malignancy scored as 4%; 30 cases of DCIS scored as 90%; and 55 cases of invasive breast carcinoma scored as 120%. The five cases of ADH examined thus far were shown to score similar to that of normal breast tissue. Conclusions: The implication of these data is that the development of a caPCNAab-based IHC stain could potentially be used to reliably stain only in situ or invasive carcinoma, and distinguish genuinely benign lesions (e.g., ADH) from carcinoma, (e.g., DCIS) allowing definitive diagnosis in such cases where a limited amount of an atypical lesion prevents definitive diagnosis on routine H/E stained sections alone. For the patient population, this could result in a marked decrease in the need for either a repeat core biopsy or an excisional biopsy due to an inconclusive initial diagnosis. No significant financial relationships to disclose.