p53 Alterations in Breast Cancer Related to Prognosis and Results of Therapy

Sammanfattning: Breast cancer is the most common malignant tumour disease and also the main cause of cancer-related deaths among women. The lifetime risk in western countries is 10%. The basic treatment for a patient with a localised tumour is surgery. In addition, different pathobiological variables are considered and an estimation of the risk of recurrence is made before deciding whether adjuvant therapy should be recommended. This therapy can be chemotherapy, which mainly prevents distant recurrence, or radiotherapy, which is effective against local recurrence. The treatment can be combined with anti-oestrogen, which prevents distant recurrence among patients exhibiting an oestrogen-receptor-positive tumour. However, breast cancer remains the chief cause of cancerrelated deaths and there is a need· for further pathobiologica! variables that, at an early stage, both can be prognostic and predict the outcome of adjuvant therapy.The p53 gene and its product p53 have been shown to play a central role in tumour suppression by regulating the cell cycle or initiating apoptosis. Certain mutations are associated with a stabilisation of the protein, leading to an accumulation that is detectable by immunohistochemistry.The main purposes of this study were to analyse p53 protein accumulation and gene mutation in exons 5-8 and to investigate the prognostic and predictive role of p53.p53 protein accumulation was investigated with immunohistochemistry in frozen tumour samples from 776 patients; 164 patients with stage U, 205 patients with stage I and 407 patients with either lymph node metastases and/or a tumour diameter exceeding 30mm. Of the latter, 139 were premenopausal and 268 were postmenopausal. These 407 patients had been randomiscd to adjuvant CMF chemotherapy or postoperative radiotherapy. Gene analyses with PCR-SSCP followed by direct sequencing were performed in the 268 postmenopausal patients. The predictive value of p53 was only analysed in the randomised patient material.The results showed that nuclear p53 accumulation ranged between 9% and 25%. p53 accumulation was significantly associated with several pathobiological variables, "indicating an aggressive tumour, which was more likely to be oestrogen receptor negative, DNA aneuploid, and have a high S-phase fraction. p53 accumulation was also significantly correlated with an increased rate of distant recurrence, whereas mutations that were found in 16% of the 268 cases investigated were not significantly correlated with an increased risk of distant recurrence. However, the investigation of both protein accumulation and gene mutation in exons 5-8 contributed further information than was achieved with one of the methods alone. The protein accumulation reflected to a certain extent mutations of the gene, mainly missense mutations. A majority of the severe mutations that included alteration of the reading frame did not lead to any protein accumulation. Sixty-one per cent of the tumours exhibiting protein accumulation did not show any mutation in exons 5-8. Subgroups of different p53 alteration patterns seemed to be related to different prognoses.The patients with p53 altered tumours, either showing protein accumulation, gene mutation or both, benefited significantly from CMF chemotherapy compared with the radiotherapy group. This benefit could not be seen among the patients without p53 alterations. The test for interaction between p53 status and relative rate was significant. This response was most pronounced among premenopausal patients. Postmenopausal patients seemed to benefit although not significantly.In conclusion, the present study suggests that p53 accumulation is a prognostic factor associated with an increased risk of distant recurrence. p53 alteration defined as protein accumulation, gene mutation in exons 5-8, or both, was a predictor of good response to CMF chemotherapy as compared to postoperative radiotherapy. This benefit could not be seen among patients without p53-altered tumours.