Relation of estrogen and/or progesterone receptor content of breast cancer to patient outcome following adjuvant chemotherapy

Inhibition of RET increases the efficacy of antiestrogen and is a novel treatment strategy for luminal breast cancer

PURPOSE

Recent findings suggest that combination treatment with antiestrogen and anti-RET may offer a novel treatment strategy in a subset of patients with breast cancer. We investigated the role of RET in potentiating the effects of antiestrogen response and examined whether RET expression predicted the ability for tyrosine kinase inhibitor (TKI) to affect extracellular signal-regulated kinase 1/2 (ERK1/2) activation in primary breast cancer.

EXPERIMENTAL DESIGN

Growth response, ERK1/2 activation, Ki-67, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling were assessed in breast cancer cell lines in vitro and in xenografts with vandetanib and/or tamoxifen. Thirty tumors with matched normal breast tissue were evaluated for RET expression and response to TKI treatment.

RESULTS

Vandetanib potentiated the inhibitory effect of tamoxifen in hormone responsive (P = 0.01) and hormone insensitive (P < 0.001) estrogen receptor α (ERα)-positive breast cancer cells. Vandetanib significantly repressed tumorigenesis of MCF-7 xenografts (P < 0.001), which displayed decreased activation of ERK1/2 and AKT. Vandetanib and tamoxifen reduced the growth of established tumors with a greater effect of dual therapy compared with single agent (P = 0.003), with tamoxifen-reducing proliferative index and vandetanib-inducing apoptosis. In primary breast cancers, RET expression correlated with the ERα-positive subtype. Relative decrease in ERK1/2 phosphorylation with TKI treatment was 42% (P < 0.001) in RET-positive tumors versus 14% (P = ns) in RET-negative tumors.

CONCLUSIONS

Vandetanib potentiated the antigrowth effects of tamoxifen in breast cancer, which was mediated through RET activation. RET predicted response to TKI therapy with minimal effects on ERK1/2 activation in RET-negative tumors. The preclinical data support evaluation of antiestrogen in combination with TKI as a potential treatment strategy for RET-positive luminal breast cancer.

Organ Specific Tumor Markers: What's New?

Tumor markers are molecules produced in the body in response to cancer. An ideal tumor marker should have high sensitivity and specificity, should be cheap, and should be easily detected in body fluids. Identification of novel markers is important and it is expected that with the advent of newer technologies, more reliable markers will be discovered. This review discusses the currently available tumor markers for different malignancies.

High-dose chemotherapy with autologous stem-cell support as adjuvant therapy in breast cancer: overview of 15 randomized trials

PURPOSE

Adjuvant high-dose chemotherapy (HDC) with autologous hematopoietic stem-cell transplantation (AHST) for high-risk primary breast cancer has not been shown to prolong survival. Individual trials have had limited power to show overall benefit or benefits within subsets.

METHODS

We assembled individual patient data from 15 randomized trials that compared HDC versus control therapy without stem-cell support. Prospectively defined primary end points were relapse-free survival (RFS) and overall survival (OS). We compared the effect of HDC versus control by using log-rank tests and proportional hazards regression, and we adjusted for clinically relevant covariates. Subset analyses were by age, number of positive lymph nodes, tumor size, histology, hormone receptor (HmR) status, and human epidermal growth factor receptor 2 (HER2) status.

RESULTS

Of 6,210 total patients (n = 3,118, HDC; n = 3,092 control), the median age was 46 years; 69% were premenopausal, 29% were postmenopausal, and 2% were unknown menopausal status; 49.5% were HmR positive; 33.5% were HmR negative, and 17% were unknown HmR status. The median follow-up was 6 years. After analysis was adjusted for covariates, HDC was found to prolong relapse-free survival (RFS; hazard ratio [HR], 0.87; 95% CI, 0.81 to 0.93; P < .001) but not overall survival (OS; HR, 0.94; 95% CI, 0.87 to 1.02; P = .13). For OS, no covariates had statistically significant interactions with treatment effect, and no subsets evinced a significant effect of HDC. Younger patients had a significantly better RFS on HDC than did older patients.

CONCLUSION

Adjuvant HDC with AHST prolonged RFS in high-risk primary breast cancer compared with control, but this did not translate into a significant OS benefit. Whether HDC benefits patients in the context of targeted therapies is unknown.

Treatment of lymph-node-negative, oestrogen-receptor-positive breast cancer: long-term findings from National Surgical Adjuvant Breast and Bowel Project randomised clinical trials

BACKGROUND

Findings from the National Surgical Adjuvant Breast and Bowel Project B-14 and B-20 trials showed that tamoxifen benefited women with oestrogen-receptor-positive tumours and negative axillary nodes, and that chemotherapy plus tamoxifen was more effective than tamoxifen alone. We present long-term findings from those trials and relate them to age, menopausal status, and tumour oestrogen-receptor concentrations. We also discuss the extent of progress made in the treatment of such patients.

METHODS

B-14 patients were randomly assigned to placebo (n=1453) or tamoxifen (n=1439); B-20 patients to tamoxifen (n=788) or cyclophosphamide, methotrexate, fluorouracil, and tamoxifen (CMFT, n=789). Primary endpoints were recurrence-free survival and overall survival estimated according to patients' age, menopausal status, and tumour oestrogen-receptor concentration. Smoothed recurrence rates were used to measure patterns of recurrence as a continuous function of age.

FINDINGS

Compared with placebo, tamoxifen benefited women in B-14 through 15 years, irrespective of age, menopausal status, or tumour oestrogen-receptor concentration (hazard ratio [HR] for recurrence-free survival 0.58, 95% CI 0.50-0.67, p<0.0001; HR for overall survival 0.80, 0.71-0.91, p=0.0008). In B-20, the benefit from CMFT over 12 years was greater than that from tamoxifen alone (HR for recurrence-free survival 0.52, 0.39-0.68, p<0.0001; HR for overall survival 0.78, 0.60-1.01, p=0.063). When CMFT was compared with placebo, there were reductions in treatment failure of about 65% in all age-groups.

INTERPRETATION

Much benefit has been achieved in treatment of women with oestrogen-receptor-positive tumours and negative nodes. When planning systemic therapy for such patients of all ages, it should be understood that some have tumours with variable concentrations of oestrogen-receptors, a surrogate for other biomarkers associated with tumour growth and response to treatment. Older women tend to have higher tumour oestrogen-receptor concentrations and are more likely to benefit from tamoxifen than from chemotherapy; in younger women, the converse is true. Consequently, the notion that use of tamoxifen or chemotherapy should be based only on age is too restrictive.

The prognostic significance of steroid receptor activity in tumor tissues of patients with primary breast cancer

The prognostic significance of steroid-receptor activity is still debatable. Discrepancies in results are probably attributable to few patients, heterogeneous patient populations, and short follow-up. We investigated the prognostic significance of estrogen- and progesterone-receptor (ER and PgR, respectively) activity as a continuous variable in a homogeneous patient population. The prognostic significance of steroid-receptor activity was examined in 329 node-negative and 320 node-positive unselected breast cancer patients. In node-negative patients, ER values of primary tumors between 100 and 400 fmol/mg protein appeared to be a significant predictor for low risk of recurrence, whereas high ER (> 400) revealed an unfavorable prognosis. The classic cutoff level of ER (< 10 fmol/mg proteins) had no prognostic significance, however. In patients receiving adjuvant chemotherapy--the node-positive breast cancer patients--the classic cutoff value of ER (10 fmol/mg protein) predicts significantly distant metastases-free survival and overall survival only in the first 4 years of follow-up after diagnosis. Progesterone receptor is a time-dependent prognosticator in node-negative breast cancer patients (cutoff point for PgR, 80 fmol/mg). In node-positive breast cancer patients treated with chemotherapy or a combination of chemo- and hormonal therapy, PgR values lower than 60 fmol/mg had a worse prognosis. The results show the poor performance of standard cutoff points for ER and PgR positivity in predicting prognosis. Better prognosis is related to higher receptor levels but this relation is predominantly time-dependent. Moreover, patients who have high ER levels have a prognosis that is worse when compared with intermediate ER levels. Standard cutoff points for steroid receptors should not be used to select patients for prognosis.

Is the negative prognostic value of high oestrogen receptor (ER) levels in postmenopausal breast cancer patients due to a modified ER gene product?

Recently, it was found that, among post menopausal breast cancer patients receiving no adjuvant therapy, the highest oestrogen receptor (ER) levels (ER++) as opposed to the intermediate ER levels (ER+) indicated a poorer prognosis in terms of recurrence-free survival (Thorpe et al. Eur J Cancer 1993, 29A, 971-977). In the present study, we confirm, in a series of 218 node negative, postmenopausal patients in whom ER was determined using a one-dose saturating method, that ER+ tumours have a more negative effect on disease-free survival (DFS) than ER+ tumours (P = 0.02). In another series of 87 ER positive, postmenopausal patients, we found a significant correlation (P = 0.04) between the ER level and ER+R ratio (ER protein/ER-specific mRNA): the higher the ER level, the more numerous the high ER+R ratio cases (ER+R > 1.5), reflecting an imbalance between the ER protein level and ER-specific mRNA. From these results, we hypothesise that high ER levels related to a high ER+R ratio suggest the presence of a modified ER gene product.

A comparison of all-subset Cox and accelerated failure time models with Cox step-wise regression for node-positive breast cancer

Clinical studies usually employ Cox step-wise regression for multivariate investigations of prognostic factors. However, commercial packages now allow the consideration of accelerated failure time models (exponential, Weibull, log logistic, and log normal), if the underlying Cox assumption of proportional hazards is inappropriate. All-subset regressions are feasible for all these models. We studied a group of 378 node positive primary breast cancer patients accrued at the Henrietta Banting Breast Centre of Women's College Hospital, University of Toronto, between January 1, 1977, and December 31, 1986. 85% of these patients had complete prognostic factor data for multivariate analysis, and 96% of the patients were followed to 1990. There was evidence of marked departures from the proportional hazards assumption with two prognostic factors, number of positive nodes and adjuvant systemic therapy. The data strongly supported the log normal model. The all-subset regressions indicated that three models were similarly good. The variables 1) number of positive nodes, 2) tumour size, and 3) adjuvant systemic therapy were included in all three models along with one of three biochemical receptor variables 1) ER, 2) combined receptor (ER- PgR-; ER+PgR-; ER- PgR+; ER+PgR+; or 3) PgR. Better multivariate modeling was achieved by using quantitative prognostic factors, a check for appropriate underlying model-type, and all-subset variable selection. All-subset regressions should be considered for routine use with the many new prognostic factors currently under evaluation; it is very possible that there may not be a single model that is substantially better than others with the same number of variables.

Prediction of response to adjuvant chemotherapy in premenopausal lymph node positive breast cancer patients with morphometry, DNA flow cytometry and HER-2/neu oncoprotein expression. Preliminary results

The value of morphometry, DNA flow cytometry and HER-2/neu oncoprotein expression for prediction of response to adjuvant chemotherapy in premenopausal lymph node positive breast cancer patients was evaluated in a group of CMF treated patients and controls with long-term follow-up. In the treated group, the Morphometric Prognostic Index (cutpoint 1.1) was the best prognosticator (p less than 0.0001, MC = 16.9), followed by the Mitotic Activity Index, the volume percentage epithelium and the number of positive nodes. For the controls, only the % HER-2/neu oncoprotein expression revealed significant differences (p less than 0.0001, MC = 16.3). When directly comparing treated patients and controls stratified for a certain parameter, no significant differences were obtained, although a trend towards improved survival in the treated group was present for some of the subgroups for several parameters. These preliminary results indicate that morphometric features and quantitative HER-2/neu oncoprotein expression may be important factors for identifying cases that will or will not respond to adjuvant chemotherapy.

Proliferative activity of breast cancers increases in the course of genetic evolution as defined by cytogenetic analysis

The prognostic value of proliferative activity and its relationship with steroid hormone receptors and histopathological grade have been demonstrated for breast cancers. However, nothing is known about the underlying mechanisms. In order to understand the chronology of the appearance of increased proliferative activities, we used a series of 760 consecutive breast cancers for which we had obtained S-phase fractions (SPFs) by DNA flow cytometry. When the absolute difference from a DNA index of 1.00 was compared to SPFs, a significant positive correlation was obtained (r = 0.39, p < 0.0001), indicating that the probability of observing a high SPF increases when tumors progressively deviate from diploidy. A highly significant correlation was observed for the hyperploid group when hypertetraploid tumors were excluded, as the SPFs increased progressively as the DNA indices decreased from 2.00 to 1.30. This observation suggested a relationship with the evolution of chromosomal abnormalities as determined by cytogenetic analysis. Indeed, in a subset of 52 cases for which sufficient metaphases were available, there was a highly significant correlation between the SPF values and the proportion of rearranged chromosomes in the tumor cells (r = 0.60, p < 0.0001). When SPFs were separated into low or high using the median value (4.5%), a correlation also existed with the genetic evolution, since they increased from diploidy to hypodiploidy and then, after endoreduplication, from tetraploidy towards triploidy, as determined by the chromosome counts. Our results substantiate the relationship between proliferative activity and steroid hormone receptors which follow the same model.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA flow cytometric analysis of primary operable breast cancer. Relation of ploidy and S-phase fraction to outcome of patients in NSABP B-04

Between 1971 and 1974, 1665 women with primary operable breast cancer were randomized into a National Surgical Adjuvant Breast and Bowel Project (NSABP) trial (B-04) conducted to evaluate the effectiveness of several different regimens of surgical and radiation therapy. No systemic therapy was given. Cells from archival paraffin-embedded tumor tissue taken from 398 patients were analyzed for ploidy and S-phase fraction (SPF) using flow cytometry. Characteristics and outcome of patients with satisfactory DNA histograms were comparable to those from whom no satisfactory cytometric studies were available. In patients with diploid tumors (43%), the mean SPF was 3.4% +/- 2.3%; in the aneuploid population (57%), the SPF was 7.9% +/- 6.3%. Only 29.9% +/- 17.3% of cells in aneuploid tumors were aneuploid. Diploid tumors were more likely than aneuploid tumors to be of good nuclear grade (P less than 0.001) and smaller size (P equals 0.03). More tumors with high SPF were of poor nuclear grade than were tumors with low SPF (P equals 0.002). No significant difference in 10-year disease-free survival (P equals 0.3) or survival (P equals 0.1) was found between women with diploid or aneuploid tumors. Patients with low SPF tumors had a 13% better disease-free survival (P equals 0.0006) than those with a high SPF and a 14% better survival (P equals 0.007) at 10 years than patients with high SPF tumors. After adjustment for clinical tumor size, the difference in both disease-free survival and survival between patients with high and low SPF tumors was only 10% (P equals 0.04 and 0.08, respectively). Although SPF was found to be of independent prognostic significance for disease-free survival and marginal significance for survival, it did not detect patients with such a good prognosis as to preclude their receiving chemotherapy. The overall survival of patients with low SPF was only 53% at 10 years. These findings and those of others indicate that additional studies are necessary before tumor ploidy and SPF can be used to select patients who should or should not receive systemic therapy.

Prognostic indicators in invasive breast cancer

Tumor size and axillary lymph node involvement are the primary determinants of clinical course for most patients. Receptors for estrogen and progesterone are important additional prognostic factors for disease-free survival, overall survival, survival time after initial disease recurrence, and the likelihood of response to hormonal therapy. Histologic grading has merit as a prognostic factor, although poor reproducibility limits its broad application. Promising data have been emerging from the use of flow cytometry to analyze DNA content and proliferative rate. Patients with aneuploid tumors are more likely to have a shorter survival time than patients with diploid tumors. A high S-phase fraction also identifies a subset of patients at increased risk for early relapse. A combined index of ploidy and S-phase may be a more useful guide; together, diploidy and low S-phase identify a subgroup of node-negative patients at very low risk for disease recurrence. A number of oncogenes have been identified in breast cancer; amplification of the HER-2/neu gene or overexpression of the gene product may be an important prognostic indicator for node-positive patients.

Human breast cancer: identification of populations with a high risk of early relapse in relation to both oestrogen receptor status and c-erbB-2 overexpression

We recently defined a new early prognostic factor, the ER+(R) status, which permits the discrimination of a group presenting a high risk of early relapse among the ER+ patients. This group was referred to as ER+(R2) in contrast to ER+(R1) which corresponded to the group of ER+ patients having a lower risk of early relapse. Taking into account the whole population including the ER- and inflammatory tumours, we have extended this view and showed that ER+(R) status is a significant predictor of disease-free survival. Determination of c-erbB-2 mRNA levels in the same series of tumours showed that high expression of c-erbB-2 mRNA is significantly correlated with ER-, inflammatory tumours and with lymph nodes involvement. Moreover, a multivariate analysis showed that c-erbB-2 mRNA overexpression was a significant predictor of early relapse (P = 0.02), as significant as ER negativity and ER+(R2). For ER+ patients a high level of c-erbB-2 mRNA constitutes a higher risk of relapse for both ER+(R1) and ER+(R2) patients. However, in the case of ER- patients, early relapses were strongly correlated with c-erbB-2 overexpression. The counterpart of this observation is that ER- patients with no overexpression of c-erbB-2 constitute a group with a relatively good prognosis.

A clinical evaluation of nuclear estrogen receptors combined with cytosolic estrogen and progesterone receptors in breast cancer

Breast cancer tissue from 95 women was simultaneously assayed for three receptors: cytosolic estrogen (CER), cytosolic progesterone (CPR), and nuclear estrogen (NER). The main objective was to determine whether the addition of NER assay to the currently accepted practice with only CER and CPR could improve the predictive capacity of receptors. Forty-two patients were studied for response to hormone therapy and 95 patients were studied for survival; the median follow-up period was 73 months (range, 8 to 300 months). The incidence of CER+, CPR+, and NER+ was 74%, 70%, and 52%, respectively. Each receptor appeared more frequently, although not significantly so, in higher age groups. Forty percent of tumors had all three receptors positive and 14% had all negative; the remaining tumors showed all possible combinations of receptors. Both the rate of response and survival curves among 70 patients with CER+ did not show any significant difference whether NER was positive or negative. Also, among 38 patients with CER+, CPR+, and NER+, there was no significant difference in the clinical outcome as compared to 17 patients with CER+, CPR+, and NER-. Among 25 patients with CER- the rare occurrence of NER+ in only three patients did not suggest any clinical implication. It is concluded, therefore, that on overall clinical grounds the current series does not support the addition of NER assay whenever data is available on both CER and CPR.

Influence of the menstrual cycle on the concentrations of estrogen and progesterone receptors in primary breast cancer biopsies

There is controversy in the literature regarding the effects of endogenous hormones on estrogen receptors (ER) and progesterone receptors (PR) in young women with breast cancer. We studied 117 young women with primary breast cancer and assessed their breast biopsies for ER and PR. The women had a record of their last menstrual period prior to breast biopsy. The menstrual cycle was divided into four phases--early proliferative (days 1-7), late proliferative (days 8-15), early secretory (days 16-22), and late secretory (days 23-30). There were lower levels of both ER and PR in biopsies excised during the early secretory phase than in other phases of the cycle; early proliferative phase receptor positive medians of ER = 77 fmol/mg protein and PR = 467 fmol/mg protein fell to ER = 28 fmol/mg and PR = 128 fmol/mg protein in the early secretory phase.

Progesterone receptor activity and relapse-free survival in patients with primary breast cancer: the role of adjuvant chemotherapy

The prognostic significance of progesterone receptor activity (PgR) with regard to the estimated relapse-free survival (RFS) was studied in 350 one-center patients with primary breast cancer. All receptor assays were performed in one laboratory; PgR levels greater than 10 fmol/mg protein were considered positive. Univariate as well as multivariate statistical analyses were used to examine the prognostic significance of several variables. Eighty-nine of the 350 patients received adjuvant CMF chemotherapy (cyclophosphamide, methotrexate, and 5-fluorouracil). The median observation period was 69 months (range 12-125 months). In the group of 261 patients who did not receive adjuvant CMF, the PgR-status lacked prognostic significance; only the lymph node status significantly affected the RFS (p less than 0.00001). In contrast, in the CMF-treated group of patients, the PgR-status was the most powerful predictor of recurrence (p less than 0.001). Premenopausal CMF-treated patients with PgR+ tumors had a significantly longer RFS than those with PgR- tumors (p less than 0.02). The present data urge the need for a reappraisal of the prognostic significance of PgR and of the mechanism of action of adjuvant chemotherapy in primary breast cancer.

Adjuvant chemotherapy of solid tumors

Adjuvant chemotherapy for microscopic disease following eradication of clinically detectable lesions by primary surgery and/or radiotherapy is of documented benefit for some oncology patients. However, for many primary cancers efficacy is limited to specific subgroups of patients or has demonstrated no advantage over primary therapy alone. The rationale for adjuvant chemotherapy and results of selected trials are reviewed. In patients for whom adjuvant therapy is of demonstrated benefit, further trials aimed at delineation of patient selection factors, optimal chemotherapy regimens and schedules, and duration of therapy are needed; progress in adjuvant treatment of other subgroups may require development of more effective antineoplastic drugs, in addition to exploration of these factors.

Mitoxantrone, cyclophosphamide, and fluorouracil in metastatic breast cancer unresponsive to hormonal therapy

Fifty-two patients with hormonally unresponsive or estrogen receptor negative metastatic breast cancer who had not received prior chemotherapy received mitoxantrone 10 mg/m2, cyclophosphamide 500 mg/m2, and 5-fluorouracil 1000 mg/m2 (MCF) by short intravenous infusion every 21 days. Disease that was resistant or stable to this regimen was treated with doxorubicin 25 mg/m2/day for two days and vinblastine 1.4 mg/m2/day for four days (DV). Both drugs were given by continuous infusion. Thirty-one partial remissions and four complete remissions occurred after treatment with MCF. Only thirty-four evaluable patients crossed to the DV phase with partial remission (11 patients), stable (five patients), or resistant (18 patients) disease. Eleven patients' responses were upgraded. The median overall time to progression (TTP), defined as the sum of the TTP on MCF and TTP on DV, was 12 months. The median survival of all patients was 19 months. Granulocytopenia was the dose limiting toxicity for MCF, but cumulative thrombocytopenia was noted. Nausea and vomiting occurred in most patients but was mild. Severe alopecia occurred in half the patients. One patient developed congestive heart failure after receiving a cumulative dose of 206 mg/m2 of mitoxantrone. The incidence of infectious complications was 35% on each regimen; 50% of these were mild. MCF is an effective combination that was well tolerated. Objective responses, durations of response, and survival were similar, but not superior, to standard doxorubicin-based combinations. Toxicity was somewhat less.

Tumor nuclear grade, estrogen receptor, and progesterone receptor: their value alone or in combination as indicators of outcome following adjuvant therapy for breast cancer

Previous reports by us have shown that the outcome of breast cancer patients who have received systemic adjuvant therapy is influenced by tumor estrogen or progesterone receptor (ER or PR) content or by nuclear grade. This publication provides information regarding the relative merit of those three markers. Findings from patients receiving L-PAM plus 5-FU (PF) or PF plus tamoxifen (PFT) indicate that the disease-free survival and survival within each regimen was almost identical when related to either ER, PR, or nuclear grade. Those having tumors with either of the receptors greater than or equal to 10 fmol or a good nuclear grade had a better outcome through five postoperative years than did those with ER or PR 0-9 fmol or poor nuclear grade. The magnitude of the difference was similar for each of the three discriminants. Since they were found to be of equal predictive value, one marker might well serve as a substitute for another. Cox regression analyses, however, clearly indicate that ER, PR, and nuclear grade have an independent influence on outcome and that a more accurate assessment of outcome is obtained when more than one marker is employed. Thus, information should be obtained on as many markers as possible. This conclusion is supported by observations presented which indicate that nuclear grade in combination with either or both of the receptors is a better predictor than either marker alone and that, as indicated by life table probability values and relative odds ratios, an increasing number of favorable tumor prognostic indicators results in a better patient outcome particularly in PFT-treated patients. A possible explanation is considered for why the separation of receptor/nuclear grade categories is more orderly and pronounced in PF-treated patients receiving tamoxifen than in those given PF alone.

The use of FITC-conjugated monoclonal antibodies for determination of S-phase cells with fluorescence microscopy

A method is modified to determine the DNA synthesizing cells in primary human breast tumors and cells with idiopathic thrombocytopenic purpura (ITP) with FITC-conjugated monoclonal antibody against bromodeoxyuridine (FITC-M-anti-BrdUrd) and fluorescence microscopy. The DNA synthesizing cells were also determined from a portion of the same tissues by classical tritiated thymidine labeling (3HdThd) and autoradiography. The results from bromodeoxyuridine labeling index (BrdUrd-LI) and tritiated thymidine labeling index (3HdThd-LI) obtained from the same tissues were compared. The mean BrdUrd-LI for breast tumor was 5.4 +/- 1.0% and the mean 3HdThd-LI was 5.5 +/- 1.1%. Similarly, the labeling indexes obtained from mononuclear leukocytes of healthy donors had means of 0.5 +/- 0.1% and 0.6 +/- 0.1% for BrdUrd-LI and 3HdThd-LI, respectively. The change in the proliferation rate of mononuclear leukocyte population in the samples obtained from patients with ITP could be observed by both methods. The mean BrdUrd-LI of mononuclear leukocytes for this hematological disorder was 5.4 +/- 0.8%. These results suggest that was 6.1 +/- 0.8%. These results suggest that this relatively simple technique offers an alternative method for determining the DNA synthesizing cells in a given cell population.