Sex moderates circadian chemotherapy effects on survival of patients with metastatic colorectal cancer: a meta-analysis.

BACKGROUND: Molecular circadian clocks can modify cancer chemotherapy effects, with a possible moderation according to sex differences. We investigated whether sex determine the optimal delivery schedule of chemotherapy for metastatic colorectal cancer. PATIENTS AND METHODS: A meta-analysis was performed using individual data from three international Phase III trials comparing 5-fluorouracil, leucovorin and oxaliplatin administered in chronomodulated (chronoFLO) or conventional (CONV) infusions. The data from 345 females and 497 males were updated at 9 years. The main end point was survival. RESULTS: Overall survival was improved in males on chronoFLO when compared with CONV (P = 0.009), with respective median values of 20.8 (95% CL, 18.7 to 22.9) and 17.5 months (16.1 to 18.8). Conversely, median survival was 16.6 months (13.9 to 19.3) on chronoFLO and 18.4 months (16.6 to 20.2) on CONV in females (P = 0.012). The sex versus schedule interaction was a strong predictive factor of optimal treatment schedule, with a hazard ratio of 1.59 (1.30 to 1.75) for overall survival (P = 0.002) in multivariate analysis. CONCLUSIONS: Males lived significantly longer on chronomodulated chemotherapy rather than on conventional chemotherapy. The current chronoFLO schedule deserves prospective assessment as a safe and more effective first-line treatment option than conventional delivery for male patients.

High-dose definitive concomitant chemoradiotherapy in non-metastatic locally advanced esophageal cancer: toxicity and outcome.

This study is a retrospective analysis of high-dose definitive concomitant chemoradiotherapy in locally advanced esophageal cancer in a single institution. The aim of the study was to identify and quantify the toxicity associated with the high-dose treatment and to analyze the outcome of this treatment. Forty-six patients (41 men and 5 women, median age of 67.5 years) with disease stage IIA-III esophageal cancer were treated with high-dose definitive chemoradiotherapy. Thirty patients had squamous cell carcinomas and 16 had adenocarcinomas. The patients were treated with three courses of chemotherapy. Each chemotherapy course consisted of cisplatin 100 mg/m(2), day 1 and 5-Fluorouracil 1000 mg/m(2)/day, day 1-5. One course was given every 3 weeks. Concurrent radiotherapy (66 Gy/33 fractions) was administered during the last two courses of chemotherapy. Toxicity grades three and four were seen in 47.5% and 40% of the patients, respectively. Treatment related mortality occurred in one patient (2.5%) due to neutropenic septicemia. Follow-up time for surviving patients (2/46) was 45 and 112 months. For the entire study population, the median time to local recurrence in the radiotherapy field was 33 months and the median time to distant metastasis was 8.7 months, whereas median overall survival was 10.8 months and median disease-specific survival 11 months. For responders to chemoradiotherapy, the median time to local recurrence was 76 months, the median time to distant metastasis 16.8 months, the median overall survival and the median disease-specific survival for the responders were both 17 months. The 2, 3 and 5-year survival rates were 22%, 15% and 11% for the entire study population, and 31%, 24% and 17% for the responders to chemoradiotherapy, respectively. By multivariate analysis response to chemoradiotherapy and lower disease stage were positive prognostic factors for survival. The results of our study have shown that concurrent high-dose chemoradiotherapy provides long-term local tumor control in locally advanced esophageal cancer. However, toxicities following this high-dose treatment, while manageable, were significant. Survival rates were not improved by high-dose chemoradiotherapy compared with what is reported in previous studies applying lower doses of definitive chemoradiotherapy.

A randomised phase II multicentre trial of irinotecan (CPT-11) using four different schedules in patients with metastatic colorectal cancer.

The purpose of this phase II trial was to compare the efficacy, safety and pharmacokinetics of four irinotecan schedules for the treatment of metastatic colorectal cancer. In total, 174 5-fluorouracil pretreated patients were randomised to: arm A (n=41), 350 mg m(-2) irinotecan as a 90-min i.v. infusion q3 weeks; arm B (n=38), 125 mg m(-2) irinotecan as a 90-min i.v. infusion weekly x 4 weeks q6 weeks; arm C (n=46), 250 mg m(-2) irinotecan as a 90-min i.v. infusion q2 weeks; or arm D (n=49), 10 mg m(-2) day(-1) irinotecan as a 14-day continuous infusion q3 weeks. No significant differences in efficacy across the four arms were observed, although a shorter time to treatment failure was noted for arm D (1.7 months; P=0.02). Overall response rates were in the range 5-11%. Secondary end points included median survival (6.4-9.4 months), and time to progression (2.7-3.8 months) and treatment failure (1.7-3.2 months). Similarly, there were no significant differences in the incidence of grade 3-4 toxicities, although the toxicity profile between arms A, B, and C and D did differ. Generally, significantly less haematologic toxicity, alopecia and cholinergic syndrome were observed in arm D; however, there was a trend for increased gastrointestinal toxicity. Irinotecan is an effective and safe second-line treatment for colorectal cancer. The schedules examined yielded equivalent results, indicating that there is no advantage of the prolonged vs short infusion schedules.

Partially wedged beams improve radiotherapy treatment of urinary bladder cancer.

BACKGROUND AND PURPOSE: Partially wedged beams (PWBs) having wedge in one part of the field only, can be shaped using dynamic jaw intensity modulation. The possible clinical benefit of PWBs was tested in treatment plans for muscle-infiltrating bladder cancer. MATERIAL AND METHODS: Three-dimensional treatment plans for 25 bladder cancer patients were analyzed. The originally prescribed standard conformal four-field box technique, which includes the use of lateral ordinary wedge beams, was compared to a modified conformal treatment using customized lateral PWBs. In these modified treatment plans, only the anterior parts of the two lateral beams had a wedge. To analyze the potential clinical benefit of treatment with PWBs, treatment plans were scored and compared using both physical parameters and biological dose response models. One tumour control probability model and two normal tissue complication probability (NTCP) models were applied. Different parameters for normal tissue radiation tolerance presented in the literature were used. RESULTS: By PWBs the dose homogeneity throughout the target volume was improved for all patients, reducing the average relative standard deviation of the target dose distribution from 2.3 to 1.8%. A consistent reduction in the maximum doses to surrounding normal tissue volumes was also found. The most notable improvement was demonstrated in the rectum where the volume receiving more than the prescribed tumour dose was halved. Treatment with PWBs would permit a target dose escalation of 2-6 Gy in several of the patients analyzed, without increasing the overall risk for complications. The number of patients suitable for dose escalation ranged from 3 to 15, depending on whether support from all or only one of the five applied NTCP model/parameter combinations were required in each case to recommend dose escalation. CONCLUSION: PWBs represent a simple dose conformation tool that may allow radiation dose escalation in the treatment of muscle-infiltrating urinary bladder tumours.

Changes in folate status as determined by reduction in total plasma homocysteine levels during leucovorin modulation of 5-fluorouracil therapy in cancer patients.

We measured plasma total homocysteine (tHcy) in 14 patients (13 patients with colorectal cancer and 1 patient with breast cancer) during their first treatment with 5-fluorouracil (5-FU) plus leucovorin [LV (5-FULV)]. Eight of these patients were investigated a second time after 3-10 cycles (median, 4 cycles) with 5-FULV. Each cycle consisted of two administrations of 5-FU (500 mg/m2) and LV (60 mg/m2) given 24 h apart. The first administration of 5-FULV on day 1 of the first cycle induced a rapid reduction of the tHcy level from 12.5 micromol/liter (10.4-15.1 micromol/liter; geometric mean with 95% confidence interval of the mean) to 9.1 micromol/liter (7.5-11.1 micromol/liter) in 24 h. tHcy remained stable at this level after the second administration of 5-FULV. In addition, the 5-FULV regimen caused a concurrent 4-fold increase in both serum and erythrocyte folate. The fifth cycle with 5-FULV had only marginal effects on the tHcy level. 5-FU without LV modulation had no effect on the plasma tHcy or folate status in eight breast cancer patients. Our data establish the reduction of tHcy as a responsive indicator of LV pharmacodynamics.

Variation in cell yield and proliferative activity of positive selected human CD34+ bone marrow cells along the circadian time scale.

Variations in cell yield and proliferative activity of human bone marrow (BM) progenitor cells were determined with flow cytometry along the 24-h (circadian) time scale. Equal volumes of BM were aspirated every 5 h, altogether 5 times in 5 healthy men. An average 6-fold higher yield of positive selected CD34+ cells occurred in each subject when BM was aspirated during the daytime and late afternoon, while a lower yield occurred during the night. Using all CD34+ cell yield data normalized to percentage of mean, a significant time-effect was found by ANOVA (p = 0.02) and a significant circadian rhythm was detected by the least-squares fit of a 24 h cosine (p = 0.02). The 95% confidence limits of the acrophase (time of highest values) were computed to be at midday between 10:24 and 14:48 h. A highly significant correlation (p = 0.001) was found between proliferation of positive selected CD34+ cells and the more mature myeloid precursor cells from the same BM aspirates, suggesting a common temporal pattern along the circadian time scale. However, no correlation was demonstrated between proliferation and cell yield of CD34+ selected cells, suggesting that mechanisms other than variation in proliferation may cause the circadian rhythm in stem cell yield. These circadian variations in stem cell yield and proliferation suggest that proper timing within 24 h may potentially be important regarding outcome from progenitor cell harvesting and treatment with haematopoietic growth factors.

Circadian cell cycle variations of erythro- and myelopoiesis in humans.

By use of a multiparameter flow cytometric method with specific surface markers, circadian (24-h) variations in cell cycle distribution have been studied in 19 healthy male volunteers by sampling bone marrow (BM) every 4-5 h during 24-h periods. Admixture of peripheral blood during the sampling was specifically adjusted for, and the fractions of cells in DNA synthetic phase were measured for different hemopoietic cell lineages. Significant circadian variations in DNA S-phase were demonstrated both in myelo- and erythropoiesis of the human BM, with 75% (myeloid) and 80% (erythroid) of the volunteers showing highest activity (values) of DNA S-phase during the day and lowest activity (values) between midnight and 04:00 h. A temporal relationship in the circadian variation of S-phase and G2/M-phase was demonstrated between the myeloid and erythroid cell lineages. The highest fractions of S-phase cells were found in erythropoiesis, while the highest circadian stage dependent variation was found in myelopoiesis. The existence of a similar phasing in DNA synthetic activity for myelopoietic and erythropoietic cells in the human bone marrow indicates that the circadian rhythmicity of hemopoiesis may be caused by a common regulatory mechanism. These findings may be relevant with regard to optimizing the use of cytotoxic drugs and hemopoietic growth factors by taking into consideration the intrinsic (endogenous) circadian variation in proliferative activity of human BM subpopulations.

Flow cytometric measurement of DNA S-phase in human bone marrow cells: correcting for peripheral blood contamination.

The relationship between bone marrow (BM) cells with S-phase DNA content and the amount of peripheral blood contamination estimated as percentage lymphocytes+monocytes (L+MO) present in BM samples has been investigated in a total of 136 BM aspirates and biopsy expellates from 35 hematologically healthy individuals. A significant negative correlation was demonstrated between total, erythroid and myeloid BM cells in S-phase and the percentage of L+MO in the aspirates (r=0.84, 0.57 and 0.49, respectively; p<0.0001). Based on the equation of the slope of the regression line, a correction formula adjusting the measured value of BM cells in S-phase to varying amounts of L+MO percentage has been worked out for the total and erythroid BM cells. In contrast, highly proliferating myelomonocytic cells and CD34+ cells did not show any significant correlation between cells in S-phase and percentage L+MO, indicating that peripheral blood contamination of BM aspirates estimates the degree of peripheral blood contamination, as well as make possible a correct estimation of the DNA synthesis of several BM populations. The method is especially applicable when frequent BM sampling is required.

Circadian rhythm of cell division.

The existence of circadian oscillations in the level of hormones, in numerous physiological parameters, in toxicity and in behavior is now fully recognized in all living organisms. In contrast, the synchronisation and regulation of cell proliferation by circadian rhythms in vivo is only starting to be appreciated. This article reviews the experimental evidence for circadian synchronisation of cell division in different mammalian tissues (mainly the gastro-intestinal tract and hemapoietic system), including tumoral tissues. The possible causes of this coupling of the cell cycle phases to the circadian rhythm are discussed. Testing of novel antitumour agents using murine models should take into consideration the temporal difference between murine and human circadian control of proliferation (the peak of DNA synthesis occurs during the activity period, i.e. during daytime in man, and at night-time in mice and rats). Experimental and clinical data clearly support the important implications of the circadian control of the cell cycle in the optimisation of cancer chemotherapy, both for reducing toxicity and increasing the antitumour effects.

Circadian cell kinetics in humans. Aspects related to cancer chemotherapy.

A prerequisite for the investigation of cell kinetics, and especially circadian cell kinetics, has been the development from the 1950s and onwards of several methods for studying kinetic parameters in different mammalian tissues. A large number of such studies have subsequently taken place in the rodent, mostly as non-circadian experiments, but also a large number of studies have now documented on circadian proliferative rhythms in many different murine tissues. Results from cytokinetic studies in the human have also accumulated through the years. Of special interest has been the demonstration of temporal variations in rapidly proliferating tissues studies as the bone marrow and gut mucosa relative to cytotoxic anticancer therapy. Analyses of proliferation in human tumours have also indicated rhythms in malignant solid tumours. Thus, these studies have demonstrated that there exist rhythms in bone marrow and gut cytokinetics which increases the likelihood that certain times of day will be less toxic for the administration of cytotoxic drugs. Furthermore, optimizing anticancer therapy according to a circadian schedule may also increase the tumour cell death rat, due both to an indirect dose-escalating effect and a direct increased tumour effect.

Circadian phase relationships between peripheral blood variables and bone marrow proliferative activity in clinical health.

Potential life-threatening drug induced side effects to the bone marrow (BM) may be reduced by the proper timing of chemotherapy (chronotherapy) according to circadian stage. Blood and BM samples were obtained concomitantly every 4h for 24h from 16 healthy men (19 series total) to compare circadian patterns in peripheral blood (PB) as reference rhythms for BM DNA. Circadian rhythm characteristics from population mean cosinor summary follow (phi = acrophase): in PB: cortisol, p = 0.014, phi = 13:04h; leukocytes (/mm3), p = 0.001, phi = 00:16h; neutrophils (%WBC), p = 0.001, phi = 15:36h; neutrophils (/mm3), p = 0.101, phi = 22:36h; lymphocytes (%WBC), p = 0.009, phi = 03:24h; lymphocytes (/mm3), p = 0.001, phi = 0.1:40h; in BM:DNA, p = 0.014, phi = 13:04h; and CFU-GM, p = 0.041, phi = 13:12h. When all DNA synthesis (S-phase) values were correlated with PB values by repeatedly advancing the DNA values by 4h, significant correlations with cortisol were found by advancing S-phase by 8h (r = 0.19, p = 0.050). Lymphocytes correlated best with S-phase when shifted by 12h (r = 0.37, p < 0.001), while neutrophils as % of leukocytes (but not absolute counts) correlated significantly when S-phase was delayed by 4h (r = 0.35, p < 0.001). These correlations confirm the phase relationships determined for the circadian rhythms. These findings suggest that the proper timing of an optimized anticancer cytotoxic chronotherapy can be confirmed and guided via sampling of marker rhythms (such as lymphocytes) in peripheral blood which have been found to demonstrate a relatively fixed relation to the circadian stage-dependent variation in unaffected BM proliferative activity.

Circannual rhythm in DNA synthesis (S-phase) in healthy human bone marrow and rectal mucosa.

Cytotoxic anti-cancer drugs are meant to interact with tumor cells to impair the replicative and/or transcriptional functions of DNA in order to reduce proliferative rate and cause cell death. These drugs also affect rapidly proliferating healthy tissues such as the bone marrow and the gastrointestinal tract, thereby resulting in toxicity-related dose reductions and/or delays in treatment. We previously demonstrated a circadian rhythm in DNA synthesis (S-phase) of total bone marrow (BM) nucleated cells in 16 healthy, diurnally active men sampled every 4 h for 24 h (19 series). Highest values determined by flow cytometry were found near midday. We also reported a circadian rhythm in DNA synthesis of the rectal mucosa (RM) in 16 healthy men sampled every 2-3 h for 24 h under fed and fasting conditions (24 series). Highest proliferative activity as reflected by in vitro [3H]Tdr uptake, was found near the time of awakening. Circannual (about yearly) rhythmicity in cell division rates may also influence treatment effects. Our BM and RM DNA data, which were collected over several years, were reanalyzed for seasonality by ANOVA and for circannual rhythm by the least-squares fit of a 1 year cosine. Characteristics of circadian amplitudes and acrophases were also compared between seasons. In addition to a significant circadian rhythm, a significant circannual rhythm in cell proliferation in healthy BM (P = 0.008) and RM (P < 0.001) could be established on the basis of these serially independent data. The range between the lowest and highest points of the fitted 1 year cosine (circannual double amplitude) was comparable to the circadian range for BM (25%); it was at least doubled for RM (70%). Highest values occurred in the late summer for BM and mid-fall for RM. Based on limited data in some seasons, the circadian patterns were more prominent in the fall and winter, with larger amplitudes and later acrophases, when compared with summer for BM and spring and summer for RM. Thus, in addition to time of day, time of year may influence chemo- and immunotherapeutic strategies and should be considered in the design of preclinical and clinical treatment regimens and other procedures.

Flow cytometric assessment of peripheral blood contamination and proliferative activity of human bone marrow cell populations.

Bone marrow aspiration is superior to bone marrow biopsies due to less discomfort to the volunteer or patient, but it is inferior concerning the reproducibility of cytokinetic information. Therefore, a method that could select aspirates of quality and reproducibility equal to those of biopsies was sought. Low-density (mononucleated) bone marrow cells were labelled with T200 common leukocyte antigen, CD45, which differentiate cells into erythroid, myeloid, and lymphocyte + monocyte subpopulations based on their immunofluorescence intensity. A hypotonic propidium iodide solution was added, and DNA cell cycle characteristics of the total cells and the subpopulations were obtained. Twenty-two aspirations were performed on three healthy men. There was a strong negative correlation between the amount of CD45-gated lymphocytes + monocytes, indicative of peripheral blood cell contamination in the aspirate, and the percentage of total cells and subpopulations in DNA S phase. A marked reduction in the percentage of cells in S phase was observed when the lymphocyte + monocyte counts were higher than 30%; this level was used to exclude aspirates with an unacceptable degree of peripheral blood cell admixture. Twelve of the aspirates were found to be of acceptable quality due to their low lymphocyte + monocyte count. These aspirates were compared with 11 bone marrow biopsy expellates from hematologically normal patients undergoing open cardiac surgery. The 12 aspirates were found to have almost identical mean percent S-phase cells as the biopsy expellates, both for the total cell population (14% +/- 3.45% vs. 15% +/- 1.5%) and for the erythroid (24% +/- 6% vs. 24.4% +/- 3.3%) and myeloid (10% +/- 2.4% vs. 10.7% +/- 2.5%) subpopulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Current concepts for chronochemotherapy of cancer.

In this article, a survey on the concepts and scientific basis for applying chemotherapy against malignant tumors on a circadian schedule is given. The idea is to give the cytostatic drugs at times of the day when optimal effect on the tumor is achieved, but at the same time causing minimal toxic side effects. Following a brief description of the complexity of cancer tissue, some aspects of the present status of cancer chemotherapy in general are reviewed. Applications of chronobiology in cancer treatment are then surveyed together with possibilities to increase cytostatic doses and reduce side effects. When optimal tumor cell kill is achieved, the next step is to address the circadian aspects of normal organs, including the proliferative behavior of tissues with rapid cell renewal. Finally, the question of how regulatory mechanisms responsible for normal circadian rhythms can be interfered with is addressed. Cancer chronochemotherapy today combined with modern infusional technology is a promising field for improving cancer treatment in general and reducing side effects and is expected to make important progress in the near future.

DNA synthesis and ploidy in non-Hodgkin's lymphomas demonstrate intrapatient variation depending on circadian stage of cell sampling.

Significant circadian cell cycle variations with a maximal number of cells in S-phase during the night have been found in a series of 24 patients (18 men and 6 women) with histologically established non-Hodgkin's lymphomas. Pathological lymph nodes of a total of 26 patients were punctured and aspirated by fine needle technique every 4 h during a single 24-h time span. Twenty-four patients (92.3%) had Stage III or IV disease. Twelve patients (46.1%) had low grade, 10 patients (38.5%) had intermediate grade, and 4 patients (15.4%) had high grade lymphomas according to the Working Formulation. The samples were analyzed by flow cytometry, and DNA synthesis (S-phase) and ploidy were determined according to circadian stage. The individual mean 24-h S-phase varied from 2.2 +/- 1.2% (mean +/- SD) to 24.0 +/- 3.3%. Within the group of patients with low grade lymphomas, a wide range in mean S-phase from 2.4 +/- 1.2% to 9.2 +/- 2.8% was observed. The percentage variation within each patient between the lowest and highest S-phase as compared to the lowest value (range of change) during the 24-h time span varied from 21 to 353%, with a mean range of change of 128 +/- 19%. When each individual S-phase series was converted to percent of mean and combined for analysis by one-way analysis of variance to test for time-effect across 2 12-h time spans (8 p.m.-8 a.m. versus 8 a.m.-8 p.m.), S-phase variation according to circadian stage was found to be statistically significant (P < 0.004), with higher values found in the 8 p.m.-8 a.m. time span. By single cosinor analysis, S-phase yielded a near significant P value of 0.069 for the least-squares fit of a 24-h cosine to all data as percent of mean, with the acrophase found to be near midnight (0.05 h). For those patients with low and intermediate grade lymphomas and with mean S-phase values < 10.0%, we found that mean S-phase was higher during winter (5.8 +/- 0.4%) than during spring (3.8 +/- 0.3%) or during fall (3.6 +/- 0.3%) (P < 0.001, analysis of variance). Twenty-one of the 26 patients (80.8%) had an aneuploid, hypodiploid, or near diploid population in one or several of the repeated samples. For the whole series, the DNA indices for the aneuploid populations varied from 1.09 to 1.96, the median DNA index being 1.20.(ABSTRACT TRUNCATED AT 400 WORDS)

Circadian variation in serum cortisol and circulating neutrophils are markers for circadian variation of bone marrow proliferation in cancer patients.

Serum cortisol, circulating white blood cells and DNA cell cycle distribution in bone marrow cells were measured during daytime (11.00) and at midnight (24.00) over single 24-hour periods in 15 cancer patients. The neutrophils and fraction of bone marrow cells in S-phase showed the same circadian variation as cortisol with higher values in daytime as compared to midnight in 11 patients with a normal cortisol rhythm (p < 0.05). The lymphocytes, eosinophils and basophils all had significantly higher values at midnight as compared to daytime. There were significant correlations between cortisol and neutrophils, lymphocytes, eosinophils and basophils. The correlation between neutrophils and fractions of bone marrow cells in S-phase and S + G2/M-phase were highly significant (r = 0.74, p = 0.0001 and r = 0.72, p = 0.0001, respectively). In 8 of 13 patients (61.5%) without bone marrow infiltration both cortisol and neutrophils showed identical circadian variation as bone marrow cells in S-phase and S + G2/M-phase. Furthermore, for the total series a significant correlation between S-phase, cortisol and neutrophils was found by multiple regression analysis (p < 0.0001). These findings strengthen the possibility of using the circadian variation in cortisol and neutrophils as marker rhythms for circadian variation in bone marrow proliferation, thus allowing optimization of cytotoxic therapy and individualization of chronotherapy.

DNA cell cycle distribution and glutathione (GSH) content according to circadian stage in bone marrow of cancer patients.

DNA cell cycle distribution and glutathione (GSH) content in bone marrow were measured both at daytime and midnight over single 24 h periods in 15 cancer patients. Between patients the S-phase demonstrated a difference from lowest to highest value of 700%, whereas the corresponding difference for the G2/M-phase was nearly 900%. The mean GSH content measured in the bone marrow at the two timepoints was 2.24 +/- 0.21 nmol mg-1 protein, range 0.91-4.19 nmol mg-1 protein. A statistically significant higher fraction of cells in S-phase and G2/M-phase was found at daytime as compared to midnight when excluding the four patients with an abnormal circadian variation in cortisol. No significant temporal variation in total bone marrow GSH content was found, although a weak correlation between S-phase and GSH content was demonstrated (r = 0.42; P less than 0.05). This correlation was strengthened when not including the six patients with an abnormal cortisol pattern (4) and bone marrow infiltration (2) (r = 0.66; P = 0.005). Cells in S-phase demonstrated a positive correlation with cells in G2/M-phase (r = 0.64; P less than 0.0001). A negative correlation was found between GSH content and age (r = 0.53; P less than 0.005). Finally, a statistically significant positive correlation was demonstrated between cortisol and both S-phase and G2/M-phase (r = 0.57; P less than 0.001 and r = 0.38; P less than 0.05, respectively). The present study suggests a possibility of optimising cancer therapy and use of hematopoietic growth factors by determining individual average values and circadian stage dependent variation in bone marrow DNA cell cycle distribution. Furthermore, GSH content in bone marrow may predict this tissue's sensitivity to cytotoxic agents.