pS2 in Breast Carcinoma: Association with Steroid Hormone Receptor Status

AIMS AND BACKGROUND

Knowledge of the steroid hormone receptors has proved to be of significant value in breast cancer. In the present study the possible importance of estrogen-regulated pS2 protein was investigated. Our direct purpose was to answer the question whether the expression of pS2 may be a marker of functional heterogeneity with respect to the steroid hormone receptor status.

METHODS AND STUDY DESIGN

The study included 152 patients with primary, operable, histologically confirmed breast carcinomas. Histology specimens were reviewed and classified according to type, nodal status, tumor size and grade. Steroid hormone receptors were assayed by biochemical methods according to the procedures recommended by the EORTC. pS2 protein measurement was performed in breast carcinoma cytosols using an immunoradiometric assay. The results were analyzed by non-parametric statistical methods.

RESULTS

A statistically significant inverse correlation between pS2 protein expression and histological tumor grade was found. The expression of pS2 protein was confirmed to be correlated with steroid hormone receptor status. However, it is important to point out that in spite of these statistically significant findings there were no significant biological associations due to overlapping individual pS2 protein values. The baseline level of expression of pS2 protein was obtained in histological grade III carcinomas with a negative steroid hormone receptor status. It was shown that the distribution of carcinomas according to the baseline level of pS2 protein expression was heterogeneous among estrogen receptor-positive carcinomas, and strikingly homogeneous among estrogen and progesterone-negative carcinoma.

CONCLUSION

Our study suggested that PR and pS2 protein may identify distinct subsets of estrogen receptor-positive breast carcinomas.

Correlation between pS2 protein positivity, steroid receptor status and other prognostic factors in breast cancer

The cytosolic levels of pS2, an estrogen-regulated protein, were measured in 100 cases of primary breast cancer and related to several conventional histological and biochemical prognostic factors. The data were statistically analyzed on the basis of two different cutoff points for pS2: 4 and 11 ng/mg of cytosolic proteins. pS2 positivity (cutoff 11 ng/mg) was shown to be associated with smaller tumor size (p = 0.05), a higher differentiation grade (p = 0.007) and a smaller number of mitoses (p = 0.004), but not with menopausal status, lymph node involvement, cathepsin D levels, or proliferative activity determined by the monoclonal antibody Ki67. With the cutoff of 4 ng/mg, the statistical significance was confirmed only for the number of mitoses (p = 0.03), which was also the most closely related covariate in multivariate analysis (p = 0.008). As regards steroid receptor status, a significant difference was observed between pS2+ and pS2– cases (Chi-square = 8.9; p - 0.04, cutoff 4 ng/mg). In conclusion, pS2 positivity, being preferentially expressed in hormone-dependent cells and related to other well-known positive markers, may either indicate a good prognosis or predict responsiveness to endocrine treatment.

Quantitative measurements of trefoil factor family peptides: possibilities and pitfalls

The trefoil factor family (TFF) peptides TFF1, TFF2, and TFF3 are produced and secreted by mucous membranes throughout the body. Their importance for the protection and repair of epithelial surfaces is well established, and the three peptides are present in various amounts in mucosal secretions as well as in the circulation. They have been linked to both inflammatory diseases and to various types of cancer, and serum concentrations of TFF3 show a more than 47-fold increase during pregnancy. Several both commercial and in-house immunoassays exist, but a number of methodological issues remain unresolved. This review describes methodological challenges in the measurement of the peptides in humans, and summarizes current knowledge concerning the occurrence and possible significance of the peptides in human health and disease.

Biphasic Scatchard plots of oestrogen receptors are associated with low pS2 levels in human breast cancers

In a series of 100 breast tumours, oestrogen receptors (ER) were analysed by Scatchard plots, progesterone receptors (PR) by enzyme immunoassay and pS2 by an immunoradiometric assay. Scatchard analysis gave information on receptor heterogeneity in that there was a large variation in Kd values obtained, from 0.001-2.95 nM. This variation was largely confined to tumours containing less than 70 fmol receptor per mg protein, while tumours with higher receptor concentrations were a more homogeneous population with low Kd values. An obvious correlation between ER and PR was found; moreover, pS2 was correlated to both ER and PR. In addition, 20 of the 100 tumours gave biphasic Scatchard plots, indicating the presence of at least two oestrogen-binding moieties, with Kd values and concentrations both in the range of those of receptors. The tumours displaying biphasic Scatchard plots had very low pS2 expression, regardless of ER concentrations; this was not true for PR. It is suggested that variability in responses to endocrine therapy may be related to the heterogeneity of the ER present in breast tumours.

pS2 (TFF1) levels in human breast cancer tumor samples: correlation with clinical and histological prognostic markers

The expression of pS2 (TFF1) has been previously shown to identify patients with improved response to anti-hormonal therapy and more favorable outcome. In the current study, 100 human breast carcinoma samples obtained from the Manitoba Breast Tumor Bank were analyzed for pS2 mRNA using a quantitative, competitive reverse transcriptase-polymerase chain reaction (qcRT-PCR) assay. A pS2/beta-actin cut-off criterion of 0.010 was established to classify tumors as either pS2 positive or pS2 negative. pS2 mRNA levels were positively associated with both ER and PR, with the majority of ER+ (59%) and PR+ (60%) tumors also being positive for pS2. In addition, a significant linear correlation was observed between the amount of pS2 mRNA and ER (p < 0.0001) and PR (p < 0.0001) protein. pS2 mRNA levels also exhibited an inverse association with tumor size and histological grade, consistent with the observation that pS2 is primarily expressed in small (T < 2.0 cm), but well differentiated tumors (Grades I and II). No associations were observed with tumor cell type, patient age, or lymph node status. The strong correlation displayed between pS2 and a number of currently used breast cancer prognostic markers supports the clinical use of pS2 to further assess tumor status and patient outcome.

Estimation of pS2 protein level in human body fluids by a sensitive two-site enzyme immunoassay

A sensitive two-site enzyme immunoassay (EIA) system was established for human pS2 protein, a small estrogen-inducible secretory protein of unknown function originally identified in MCF-7 human breast cancer cells. Our EIA system is based on the sandwiching of antigen between anti-recombinant (r) pS2 antibody IgG coated on a polystyrene plate and biotinylated anti-rpS2 antibody IgG. The amount of pS2 protein was quantified by measurement of the bound enzyme activity of subsequently added streptavidin-linked beta-D-galactosidase (beta-D-galactosidase, EC 3.2.1.23). pS2 protein purified from MCF-7 culture supernatants was detectable at a concentration as low as 3 pg/ml (corresponding to 60 fg/well). This EIA system revealed that the amount of pS2-like immunoreactivity (LI) in human urine was 13.6 ng/mg creatinine (median, n = 416) and that there was no correlation between the pS2-LI concentration in urine and sex or aging. pS2-LI levels in plasma and sera of the normal subjects were 392 pg/ml (median, n = 14) and 494 pg/ml (median, n = 12), respectively. The serum level of the patients with breast cancer (528 pg/ml; median, n = 67) was not statistically different from that of normal subjects, although high levels of pS2 protein in breast cancer tissues had been reported.

Immunohistochemical and biochemical analysis of the oestrogen regulated protein pS2, and its relation with oestrogen receptor and progesterone receptor in breast cancer

AIMS

(i) To assess the validity of an immunocytochemical technique for detecting pS2 protein in paraffin wax embedded tissue; (ii) to provide further data on the relation between pS2 protein and oestrogen receptor (ER) and progesterone receptor (PgR).

METHODS

Breast cancer excision biopsy specimens were obtained from 35 previously untreated patients. An immunoradiometric assay was compared with an immunohistochemical method for measuring pS2 protein. ER and PgR were measured in cytosol fractions by enzyme immunoassay and the relation between the presence of these receptors and pS2 protein was assessed before and after subdivision of the women into groups of over or under 50 years of age.

RESULTS

A good correlation was seen between the immunoradiometric and immunohistochemical methods for pS2 protein measurement (r = 0.84; p = 0.0001). Log-transformed data showed a significant correlation between increasing values of ER and pS2 protein (r = 0.45; p = 0.006) and to a lesser extent between pS2 protein and PgR (r = 0.38; p = 0.03). Correlations were also shown between pS2+ and PgR+ status (p = 0.01), and between ER and PgR positivity (p = 0.05; Fisher's exact test). pS2+ protein status was only associated with ER+ status in patients aged 50 years or less.

CONCLUSIONS

The two methods for pS2 analysis are virtually interchangeable. This provides strong support for using immunohistochemistry for pS2 in paraffin wax embedded tissue. The association with ER positivity and pS2+ protein status only in the premenopausal patients may be due to the higher levels of oestrogenic stimuli in that group.

Relationships between tamoxifen binding proteins in primary breast cancer biopsies

Using high-resolution isoelectric focusing gel electrophoresis (IEF), two tamoxifen binding sites (TBS) with isoelectric point (pI) values of 4.5 and 4.3 were identified, with different affinities for tamoxifen. The form at pI 4.3 (HTBS) displayed high affinity for the ligand (kD approximately 5 nM), while the protein at pI 4.5 (LTBS) had lower affinity (kD approximately 50 nM). LTBS was found in the microsomal fraction and HTBS in the cytosol. Of a total of 319 tumours studied, 257 were oestrogen receptor (ER) positive and 106 HTBS positive. In this combined group, thus able to bind tamoxifen either through the presence of ER or HTBS (or both), ER and PR were both negatively correlated with HTBS (P < 0.0001). The oestrogen-induced protein pS2 was assayed in 92 of the 319 tumours, and was also negatively (P < 0.0001) correlated with HTBS. The levels of HTBS were similar between infiltrating ductal carcinomas without special features (NOS) and non-NOS forms. However, HTBS concentrations were significantly higher in poorly differentiated grade 3 carcinomas than grade 2 (P < 0.05) and grade 1 (P < 0.01) forms. Conversely, ER concentration was lower in grade 3 than grade 1 forms (P < 0.05). Both the relationship between high affinity TBS and ER and the high concentration of HTBS in ER-poor grade 3 carcinomas may have a bearing on the known variability of tumour response to endocrine therapy and prognosis.

Steroid receptors, pS2 and cathepsin D in early clinically node-negative breast cancer

Four oestrogen-regulated proteins of reported prognostic value, oestrogen receptor (ER), progesterone receptor (PR), pS2 and cathepsin D (Cat D), have been quantified by immunoassays, and the latter studied by immunohistochemistry (IHC) in primary tumours from clinically node-negative early breast cancer patients, entered into a trial of breast conservation therapy in which all the patients received adjuvant tamoxifen. ER, PR and pS2 significantly co-correlated but none correlated with Cat D. ER, PR and pS2, but not Cat D, were significantly associated with tumour size and grade, although Cat D tended to show an inverse relationship with the latter. Cat D (radioimmunoassay) in pmol/mg significantly correlated with the IHC score for Cat D in carcinoma cells as well as the number of Cat D-expressing macrophages. At a median follow-up of only 16 months, recurrence was significantly more common in patients with tumours having negative status for ER, PR and pS2 but was not associated with Cat D status.

Expression of pS2 protein in breast cancer

The pS2 protein was first detected in the oestrogen-dependent breast cancer cell line MCF-7. It may have prognostic value for primary breast cancer, and could be used to predict clinical responsiveness to endocrine therapy. In a retrospective study, the concentrations of pS2 protein were determined in 434 cytosol specimens using an immunoradiometric assay. The median values (4, 6 and 3 ng/mg protein) and the third quartiles (27, 26 and 29 ng/mg) in benign breast tumours (n = 17), and in primary (n = 325) and recurrent (n = 37) breast carcinomas were of the same order of magnitude. In primary breast cancer, high pS2 values (> 26 ng/mg) correlated significantly with a positive oestrogen receptor (ER) status and a high grade of tumour differentiation (P = 0.01). As many as 85% of the pS2 positive tumours were ER positive. A marginally significant correlation (P = 0.06) was also found between pS2 status and the quantitative expression of the ER. However, the pS2 values in ER positive endometrial carcinomas (n = 12) as well as in other benign and malignant genital tumours (n = 43) were more than 30 times lower than those measured in breast tumours. The results reveal a close association between pS2 protein and ER status which appears to be limited to breast cancer.

Immunohistochemistry of pS2 in normal human breast and in various histological forms of breast tumours

Expression of pS2 was studied by immunocytochemistry in normal breast tissue (n = 20), benign tumours (n = 9) and 145 breast cancers representative of the different histological types. pS2 immunostaining was scored as negative (D1 = 0-5% stained cells), positive (D2 = 5-75% stained cells) or highly positive (D3 > 75% stained cells). pS2 protein was evident in all normal breast samples examined. Six of nine benign lesions showed pS2 staining. In both cases, immunostaining was weaker than in breast cancers. Of breast cancers, 77/145 (53.1%) were pS2 positive, including 33.1% with intense staining. The presence of pS2 was not correlated with the age of patients, the size of the primary tumour, or lymph node status, but was correlated with histological grading and nuclear grading. pS2 expression was also correlated with menopausal status and oestrogen receptor status (59% of receptor-positive tumours were pS2 positive), but not to progesterone receptor status. pS2 expression in breast carcinomas is not a characteristic of specific histological types. Although this protein is predominantly expressed in oestrogen receptor-positive and differentiated tumours, it shows oestrogen-independent expression in about 30% of cases.

Clinical significance of the estrogen regulated pS2 protein in mammary tumors

A third of breast cancers are estrogen dependent and respond to endocrine therapy. The estrogen receptor (ER) was the first marker used to predict the responses to treatment, and two-thirds of ER positive tumors show a favourable response. Several estrogen-regulated proteins were further studied in a search to enhance the prediction accuracy of ER status: progesterone receptors, 24-K heat shock protein, cathepsin D, and recently pS2 protein. The pS2 gene, also named BCEI, pNR-2 [4], Md2, was first identified by two groups using differential screening of a complementary DNA library derived from a human breast carcinoma cell line (MCF-7) grown with and without estrogens. Later on two independent English groups and a Japanese group identified a gene similar to pS2. The pS2 mRNA, relatively abundant (0.8%) in the MCF-7 cell line when stimulated by estrogens, encodes a cystein-rich, 84 aminoacids peptide which is secreted by breast cancer cells. The expression of the pS2 gene, pS2 protein assays in tumor cytosols and more recently pS2 detection by immunocytochemistry, have been described in several series of breast cancers.

Relationships between oestrogen-inducible proteins, oestradiol and electrolyte ratio in breast cyst fluid

Women who have breast cysts with intracystic Na+/K+ < 3 may have a higher risk of developing breast cancer than women who have breast cysts with intracystic Na+/K+ > 3. In this study wide-ranging intracystic concentrations of cathepsin D and pS2 (oestrogen inducible proteins/polypeptides) as well as oestradiol were found. The concentrations of cathepsin D and oestradiol were significantly higher in the low electrolyte ratio cyst group than in the high electrolyte ratio cyst group. No significant difference was found between pS2 concentrations in the two groups. The significantly higher intracystic concentrations of cathepsin D, a mitogenic lysosomal endopeptidase and oestradiol in the low electrolyte ratio group may partly provide an explanation for the higher risk of breast cancer which has been observed in this group of women.