ΔNp63, also known as p40, regulates stemness of normal mammary gland epithelium and provides stem cell characteristics in basal and HER2-driven murine breast cancer models. Whilst ΔNp63/p40 is a characteristic feature of normal basal cells and basal-type triple-negative breast cancer, some receptor-positive breast cancers express ΔNp63/p40 and its overexpression imparts cancer stem cell-like properties in ER+ cell lines. However, the incidence of ER+ and HER2+ tumours that express ΔNp63/p40 is unclear and the phenotype of ΔNp63/p40+ cells in these tumours remains uncertain. Using immunohistochemistry with p63 isoform-specific antibodies, we identified a ΔNp63/p40+ tumour cell subpopulation in 100 of 173 (58%) non-triple negative breast cancers and the presence of this population associated with improved survival in patients with ER- /HER2+ tumours (p = 0.006). Furthermore, 41% of ER+ /PR+ and/or HER2+ locally metastatic breast cancers expressed ΔNp63/p40, and these cells commonly accounted for <1% of the metastatic tumour cell population that localised to the tumour/stroma interface, exhibited an undifferentiated phenotype and were CD44+ /ALDH- . In vitro studies revealed that MCF7 and T47D (ER+ ) and BT-474 (HER2+ ) breast cancer cell lines similarly contained a small subpopulation of ΔNp63/p40+ cells that increased in mammospheres. In vivo, MCF7 xenografts contained ΔNp63/p40+ cells with a similar phenotype to primary ER+ cancers. Consistent with tumour samples, these cells also showed a distinct location at the tumour/stroma interface, suggesting a role for paracrine factors in the induction or maintenance of ΔNp63/p40. Thus, ΔNp63/p40 is commonly present in a small population of tumour cells with a distinct phenotype and location in ER+ and/or HER2+ human breast cancers.

• Keywords
• CD44, HER2, aldehyde dehydrogenase, breast, cancer stem cells, oestrogen receptor, p40, p63, ΔNp63,
• MeSH
• Phenotype MeSH
• Heterografts MeSH
• Humans MeSH
• Mice MeSH
• Biomarkers, Tumor analysis   metabolism   MeSH
• Neoplastic Stem Cells metabolism   pathology   MeSH
• Tumor Suppressor Proteins metabolism   MeSH
• Breast Neoplasms genetics   metabolism   pathology   MeSH
• Receptor, ErbB-2 genetics   metabolism   MeSH
• Receptors, Estrogen genetics   metabolism   MeSH
• Transcription Factors metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ERBB2 protein, human MeSH Browser
• Biomarkers, Tumor MeSH
• Tumor Suppressor Proteins MeSH
• Receptor, ErbB-2 MeSH
• Receptors, Estrogen MeSH
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH

The TP63 gene encodes two major protein variants that differ in their N-terminal sequences and have opposing effects. In breast, ΔNp63 is expressed by immature stem/progenitor cells and mature myoepithelial/basal cells and is a characteristic feature of basal-like triple-negative breast cancers (TNBCs). The expression and potential role of TAp63 in the mammary gland and breast cancers is less clear, partly due to the lack of studies that employ p63 isoform-specific antibodies. We used immunohistochemistry with ΔNp63-specific or TAp63-specific monoclonal antibodies to investigate p63 isoforms in 236 TNBCs. TAp63, but not ΔNp63, was seen in tumour-associated lymphocytes and other stromal cells. Tumour cells showed nuclear staining for ΔNp63 in 17% of TNBCs compared to 7.3% that were positive for TAp63. Whilst most TAp63+ tumours also contained ΔNp63+ cells, the levels of the two isoforms were independent of each other. ΔNp63 associated with metaplastic and medullary cancers, and with a basal phenotype, whereas TAp63 associated with androgen receptor, BRCA1/2 wild-type status and PTEN positivity. Despite the proposed effects of p63 on proliferation, Ki67 did not correlate with either p63 isoform, nor did they associate with p53 mutation status. ΔNp63 showed no association with patient outcomes, whereas TAp63+ patients showed fewer recurrences and improved overall survival. These findings indicate that both major p63 protein isoforms are expressed in TNBCs with different tumour characteristics, indicating distinct functional activities of p63 variants in breast cancer. Analysis of individual p63 isoforms provides additional information into TNBC biology, with TAp63 expression indicating improved prognosis.

• Keywords
• Androgen receptor, BRCA1, BRCA2, PTEN, TAp63, Triple-negative breast cancer, ΔNp63,
• MeSH
• Phenotype MeSH
• PTEN Phosphohydrolase genetics   MeSH
• Humans MeSH
• Neoplasm Recurrence, Local genetics   MeSH
• Mutation genetics   MeSH
• Tumor Suppressor Proteins genetics   MeSH
• Protein Isoforms genetics   MeSH
• BRCA1 Protein genetics   MeSH
• BRCA2 Protein genetics   MeSH
• Gene Expression Regulation, Neoplastic genetics   MeSH
• Transcription Factors genetics   MeSH
• Triple Negative Breast Neoplasms genetics   metabolism   mortality   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• BRCA1 protein, human MeSH Browser
• BRCA2 protein, human MeSH Browser
• PTEN Phosphohydrolase MeSH
• Tumor Suppressor Proteins MeSH
• Protein Isoforms MeSH
• BRCA1 Protein MeSH
• BRCA2 Protein MeSH
• PTEN protein, human MeSH Browser
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH