G. Westhof et al., QUANTITATIVE-ANALYSIS OF P53 PROTEIN IN B ENIGN AND MALIGNANT BREAST TISSUES, Geburtshilfe und Frauenheilkunde, 57(6), 1997, pp. 342-348
Most of the previous studies on the prognostic significance of p53 exp
ression in breast cancers were based on immunohistochemical methods an
d gave contradictory results. This problem might be due to subjective
evaluation of tissue staining and arbitrary definition of a threshold
to separate ''p53 positive'' from ''p53 negative'' samples. The invest
igator's influence could be avoided by quantitative determination of p
53 protein concentrations. In this study, a luminometric assay was use
d to measure p53 protein concentrations in breast cancer tissues (n =
99). Preparation of tissue samples and cytosols was identical to that
used in the Abbott steroid receptor assay. To define an upper normal l
imit (cut off), samples from healthy or benign parenchymal tissues (n
= 40) were analysed. In addition, histologically normal lymph nodes (n
= 6) and axillary lymph node metastases (n = 8) were examined. Determ
ination of total protein concentrations in cytosols allowed for the p5
3 protein concentrations to be given in ng/mg protein - similar to the
receptor assay procedure. In control tissues, a wide range of p53 con
centrations (less than or equal to 0.01 -0.76 ng/mg protein, median: 0
.035 ng/mg protein) was found. The upper 5 %-confidence limit of 0.111
ng/mg protein was used as upper normal limit (cut off). When data wer
e qualitatively evaluated, 66% of invasive carcinomas (65/99) and 5 of
8 lymph node metastases showed elevated p53 concentrations. The relat
ive frequency of elevated p53 concentrations demonstrated a significan
t relationship to the histological grading of carcinomas (CI: 36%; GII
: 72%; GIII: 78%), but not to the nodal or receptor status. However, m
ore information could be obtained from quantitative comparison of p53
concentrations: The total group of invasive carcinomas demonstrated si
gnificantly higher p53 concentrations than the controls (p < 0.0003).
In nodal positive and receptor negative carcinomas concentrations were
somewhat higher than in nodal negative and receptor positive tumours,
respectively, although these differences were not significant. The de
gree of histological malignancy was positively related to an increase
in p53 concentrations. All differences between the subgroups CI, CII a
nd GIII were significant (p = 0.0066 to p = 0.0384). In summary, breas
t carcinomas of higher histological degrees of malignancy demonstrated
higher concentrations of p53 protein than tumours of relatively low g
rade of malignancy. In breast cancers, the rate of elevated p53 protei
n concentrations seems to exceed the frequency of mutations in the pro
tein-coding regions of the p53 gene.