Mutant p53 protein overexpression in women with ipsilateral breast tumor recurrence following lumpectomy and radiation therapy.

BACKGROUND

The p53 tumor suppressor gene encodes a nuclear phosphoprotein that is thought to be important to cell cycle regulation and DNA repair and that also may regulate induction of apoptosis by ionizing radiation. Somatic p53 gene mutations occur in 30-50% of breast carcinomas and are associated with poor prognosis. Mutations in the p53 gene result in prolonged stability of the protein that can be detected by immunohistochemical techniques. In a matched case-control study of breast carcinoma patients with ipsilateral breast tumor recurrence (IBTR) following lumpectomy and radiation therapy, the authors investigated the frequency and prognostic significance of somatic p53 mutations as well as the clinical characteristics of patients with these mutations.

METHODS

Between 1973 and 1995, there were 121 breast carcinoma patients with IBTR following lumpectomy and radiation therapy, and the authors identified 47 patients in whom the paraffin embedded tissue blocks from the primary breast tumors were available for further molecular analysis. Forty-seven control breast carcinoma patients from the breast carcinoma data base were individually matched to the index cases who did not have IBTR for age, treatment date, follow-up, histology, margin status, radiation dose, and adjuvant treatment. Immunohistochemistry using a monoclonal antibody to mutant p53 protein was used to determine mutant p53 protein overexpression in breast tumors and appropriately scored.

RESULTS

A total of 12 of 47 tumor specimens (26%) from index patients with breast tumor relapses demonstrated mutant p53 protein overexpression, whereas only 4 of 47 specimens from controls (9%) demonstrated high mutant p53 immunoreactivity (P = 0.02). The authors found that 9 of 23 patients (39%) with early breast tumor recurrences (recurrences within 4 years of diagnosis) had overexpression of mutant p53 protein, whereas only 1 of 23 control cases (4%) had high mutant p53 protein immunoreactivity (P = 0.003). In contrast, index cases from patients with late breast tumor relapses (more than 4 years after diagnosis), which are more likely to represent de novo breast tumors, and control cases from the breast carcinoma data base without IBTR had similar levels of mutant p53 protein overexpression (P = not significant). The 10-year distant disease free survival for patients with mutant p53 protein was 48%, compared with 67% for breast carcinoma patients without detection of mutant p53 protein (P = 0. 08). The authors found that 13 of 14 primary breast tumors (93%) with mutant p53 protein overexpression were estrogen receptor negative (P = 0.01) and 11 of 14 (79%) were progesterone receptor negative (P = not significant).

CONCLUSIONS

In a matched case-control study, overexpression of mutant p53 protein has prognostic significance with respect to IBTR following lumpectomy and radiation therapy. Breast tumors with p53 mutations are generally estrogen receptor negative and are associated with compromised distant disease free survival.