We previously reported that high tumour cell proliferation evaluated by Ki-67 expression, high mitotic frequency and high histological grade were associated with resistance to primary doxorubicin monotherapy in locally advanced breast cancer harbouring wild-type (wt) TP53. The aim of our present study was to evaluate the predictive and prognostic impact of proliferation parameters assessed in tumour tissue obtained after chemotherapy, and alterations induced in tumour cell proliferation. While we found a significant reduction in Ki-67 expression and mitotic frequency in tumours with wtTP53 (p=0.001 and p=0.008, respectively), no significant change was recorded in tumours expressing mutant TP53. For histological grade there was no significant change in either group. There was a direct correlation between pre- and post-treatment values for Ki-67 and mitotic frequency in tumours harbouring wtTP53 (p=0.0001 for both), but no correlation in tumours harbouring mutated TP53. High post-treatment Ki-67 expression and mitotic frequency were found to predict doxorubicin resistance only in patients with wtTP53 (p=0.04 and p=0.03, respectively). The prognostic importance of proliferation markers and histological grade was found to be similar whether they were determined in the pre- or post-treatment samples (Ki-67; pre: p=0.02; post: p=0.03; mitotic frequency; p=0.002 and p=0.01, respectively; histological grade; p=0.0001 and p=0.002, respectively). While the reduction in mitotic frequency was associated with improved survival (p=0.03), no significant associations between changes in other parameters and outcome were recorded.

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