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p16INK4A as a predictive factor in patients with locally advanced breast cancer treated with neoadjuvant doxorubicin monotherapy

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The cyclin-dependent kinase inhibitor p16 (p16INK4A/ CDKN2A) binds to Cdk4 and inhibits the formation of the Cdk4/cyclin D1 complex, thereby inhibiting the cyclin D-dependent phosphorylation of the retinoblastoma protein (pRb). Phosphorylation of pRb leads to release of the E2F transcription factor that activates genes promoting cell cycle progression from G1 to S-phase. Alterations of p16INK4A, leading to its inactivation, result in the deregulation of cell proliferation through loss of G1 arrest control, and can thereby contribute to the formation of cancer and may influence tumour response to chemotherapy. To investigate the role of p16INK4A as a predictive factor in the neoadjuvant treatment of patients with breast cancer, we have analysed the p16 status in a series of 91 patients treated for locally advanced breast cancer with doxorubicin monotherapy. We measured p16INK4A protein expression with use of immunohistochemistry, studied possible mutations by direct sequencing of exon 1 and 2, and determined the methylation status of CpG sites in exon 1α . Of 90 tumours examined by immunostaining, 28 were negative or expressed p16INK4A at low levels (grade 1 = <5% positively stained tumour cells), 35 had a moderate p16INK4A expression (grade 2 = 5-50% positively stained tumour cells), and 27 had strong expression of p16INK4A (grade 3 = >50% positively stained tumour cells). One tumour had a missense mutation in codon 145 in addition to methylation of exon 1α (p16INK4A immunostaining grade 3), and three tumours displayed methylation of exon 1α (2 showed p16INK4Aimmunostaining grade 1, and 1 showed p16 INK4A immunostaining grade 2). One tumour with methylation of exon 1α has previously been reported to have a mutation of TP53 affecting the L2/L3 domains. p16 INK4A methylation correlated with lack of response to doxorubicin treatment; 2/4 patients with p16INK4A methylation progressed on therapy, compared to 7/86 without p16 INK4Amethylation (P = 0.048). On the contrary, p16INK4Aimmunostaining did not correlate with treatment response, nor with immunostaining for pRb, p19ARF, cyclin D1 and cyclin E, nor mutational analyses for TP53. Our data suggest that p16INK4A alterations may be involved in chemoresistance in breast cancer, although immunostaining alone fails to show a predictive value for response to doxorubicin treatment.

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Geisler, S., Smith-Sørensen, B., Betticher, D. et al. p16INK4A as a predictive factor in patients with locally advanced breast cancer treated with neoadjuvant doxorubicin monotherapy. Breast Cancer Res 2 (Suppl 1), P5.01 (2000).

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