The role of hemoglobin concentration in the outcome of misonidazole-sensitized radiotherapy of head and neck cancers: based on RTOG trial #79-15

EPOETIN A ALFA IN RADIOTERAPIA

Sixty per cent of oncologic patients need radiation therapy for cure or palliation. In fact, in most neoplastic diseases, a better local control positively impacts on disease-free survival and overall survival. The efficacy of radiotherapy depends on several factors: while some are tumor-related, others are host-related.

Radiobiological phenomena are also important: ionizing radiation is responsible for cell damage (double rupture of DNA chains), mostly an indirect mechanism with the formation of free radicals. Their toxic action is enhanced by the oxygen partial pressure at the cellular level.

A number of studies have confirmed that good tissue oxygenation is a function of a high hemoglobin level in the peripheral blood (Hb≥13g/dL). Unfortunately, these values are rarely present in oncologic patients due to the disease-related toxicosis as well as to the therapy induced hematologic toxicity.

The treatment of anemia is free of risk for the recent developments in technology which with gene cloning and the technique of recombinant DNA has allowed the production of human recombinant erythropoietin.

Erythropoietin is produced by the interstitial cells of renal tubules in response to hypoxia. It prevents apoptosis and promotes erythroid proliferation and differentiation with consequent reticulocyte release and hemoglobin synthesis.

It is not completely understood whether the efficacy of radiotherapy depends on hemoglobin values present at the start of irradiation (often less than 12-13 g/dL) or on the higher ones observed during and at the end of radiotherapy.

Therefore, preventive systemic erythropoietin therapy in non anemic patients in terms of costs/benefits is at present non sustainable.

To the contrary, in patients undergoing radiotherapy to extended fields or aggressive multimodal treatments, for the higher risk of anemia, the early use of this treatment can be hypothesized in case of initial anemia to improve therapy compliance and prevent negative conditioning of results.

Keeping in mind that grade 1 minimum toxicity for red cells, according to the Radiation Therapy Oncology Group (RTOG) is equal to 11gHb/dL we think that this value can be considered as cutoff to start erythropoietin therapy.

Hypoxic modification of radiotherapy in squamous cell carcinoma of the head and neck--a systematic review and meta-analysis

BACKGROUND

The importance of tumour hypoxia for the outcome of radiotherapy has been under investigation for decades. Numerous clinical trials modifying the hypoxic radioresistance in squamous cell carcinoma of the head and neck (HNSCC) have been conducted, but most have been inconclusive, partly due to a small number of patients in the individual trial. The present meta-analysis was, therefore, performed utilising the results from all clinical trials addressing the specific question of hypoxic modification in HNSCC undergoing curative intended primary radiotherapy alone.

METHODS

A systematic review of published and unpublished data identified 4805 patients with HNSCC treated in 32 randomized clinical trials, applying, normobaric oxygen or carbogen breathing (5 trials); hyperbaric oxygen (HBO) (9 trials); hypoxic radiosensitizers (17 trials) and HBO and radiosensitizer (1 trial). The trials were analysed with regard to the following endpoints: loco-regional control (32 trials), disease specific survival (30 trials), overall survival (29 trials), distant metastases (12 trials) and complications to radiotherapy (23 trials).

RESULTS

Overall hypoxic modification of radiotherapy in head and neck cancer did result in a significant improved therapeutic benefit. This was most dominantly observed when using the direct endpoint of loco-regional control with an odds ratio (OR) of 0.71, 95% cf.l. 0.63-0.80; p<0.001), but this was almost mirrored in the disease specific survival (OR: 0.73, 95% cf.l. 0.64-0.82; p<0.001), and to a lesser extent in the overall survival (OR: 0.87, 95% cf.l. 0.77-0.98; p=0.03). The risk of distant metastases was not significantly influenced although it appears to be less in the tumours treated with hypoxic modification (OR: 0.87, 95% cf.l. 0.69-1.09; p=0.22), whereas the radiation related late complications were not influenced by the overall use of hypoxic modifications (OR: 1.00, 95% cf.l. 0.82-1.23; p=0.96). The improvement in loco-regional control was found to be independent of the type of hypoxic modification. The trials have used different fractionation schedules, including large doses per fraction, which may result in relatively more hypoxia and greater benefit. However, analysis of HNSCC trials using conventional fractionation only, showed that the significant effect of hypoxic modification was maintained.

CONCLUSION

The meta-analysis thus demonstrates that there is level 1a evidence in favour of adding hypoxic modification to radiotherapy of squamous cell carcinomas of the head and neck.

New and emerging radiosensitizers and radioprotectors

The combination of chemotherapy and radiation has led to clinical breakthroughs in several disease sites, and current work continues to define optimum combinations of proven chemotherapy as well as more recently available, noncytotoxic agents. Administration of systemic therapies allows modulation of radiation response to improve tumor control (radiosensitization) or to prevent normal tissue toxicity (radioprotection). Substantial progress has been made in identifying the targets of standard chemotherapeutic radiation sensitizers and protectors as well as in the introduction of a new generation of molecularly targeted therapies in combination with radiation. We have reviewed the most recent, predominantly early phase clinical trials combining systemic agents with radiation. Although the proof of an improved schedule ultimately needs to come from well-run Phase III trials, the search among schedules could be shortened by the use of surrogate endpoints such as presence of active drug metabolites in the tumor. This has been accomplished only in a few cases and needs to become a more standard part of radiation sensitizer and protector trials.

Pretreatment anemia is correlated with the reduced effectiveness of radiation and concurrent chemotherapy in advanced head and neck cancer

PURPOSE

Pretreatment anemia is an adverse prognostic variable in squamous cell head-and-neck cancer (HNC) patients treated with radiotherapy (RT) alone. Tumor hypoxia is an adverse parameter for treatment with RT alone or with RT and concurrent chemotherapy (CCT). Tumor hypoxia is more prevalent in patients who present with pretreatment hemoglobin (Hgb) concentrations less than 13 g/dL. RT/CCT improves survival over RT alone in advanced HNC, and its use is becoming more widespread. This study was performed to evaluate whether pretreatment Hgb less than 13 g/dL was correlated with treatment outcome in patients with advanced HNC treated with a uniform regimen of RT/CCT.

METHODS AND MATERIALS

The study population consisted of patients with AJCC Stage III or IV, M0 HNC who were treated with 70 to 72.5 Gy accelerated hyperfractionated RT (1.25 Gy b.i.d.) and CCT consisting of 2 cycles of CDDP (12-20 mg/m(2)/d x 5 days) and continuous infusion 5-FU (600 mg/m(2)/d x 5 days) during Week 1 and Week 6. A planned break in RT occurred during Week 4. These patients were enrolled on the experimental arm of a prospective randomized trial that compared this regimen to hyperfractionated irradiation alone from 1990 to 1996. RT/CCT was delivered as standard therapy from 1996 to 2000. The primary endpoint was failure-free survival (FFS). Secondary endpoints included local-regional control and overall survival.

RESULTS

One hundred and fifty-nine patients were treated from 1990 to 2000. The median (25-75%) pretreatment Hgb was 13.6 (12.2-13.5) g/dL. Hgb was 13 g/dL or higher in 105 patients and less than 13 g/dL in 54 patients. Primary tumor sites included oropharynx (43%), hypopharynx/larynx (36%), oral cavity (9%), and nasopharynx (6%). Seventy-eight percent of the patients with Hgb 13 g/dL or higher and 92% of the patients with Hgb less than 13 g/dL had a primary tumor stage of T3 or T4 (p = 0.01). Node-positive disease was present in 74 of 105 (70%) of patients with Hgb 13 g/dL or higher patients and in 36/54 (67%) of patients with Hgb less than 13 g/dL patients. Median follow-up of surviving patients was 42 months (range, 4-128 months). Five-year FFS was 75% for patients with Hgb 13 g/dL or higher vs. 50% for patients with Hgb less than 13 g/dL had a (p < 0.01). A total of 49 failures occurred in both patient cohorts. The median (25-75%) decrease in Hgb during RT/CCT was 2.2 (1.3-3.1) g/dL, both in patients who failed and in those who remained disease-free.

CONCLUSION

Pretreatment Hgb less than 13 g/dL is correlated with adverse outcomes in advanced HNC patients treated with RT/CCT. Whether anemia actually causes poor outcomes remains unknown. The therapeutic effect of anemia correction is being evaluated in prospective trials.

Impact of anemia in patients with head and neck cancer treated with radiation therapy

Locoregional recurrence remains a major obstacle to achieving a cure of locally advanced head and neck cancers, despite multimodality therapy. Multiple studies report that a low hemoglobin (Hgb) before or during radiation therapy is an important risk factor for poor locoregional disease control and survival. Anemia is common in the head and neck cancer population and is suspected to contribute to intratumoral hypoxia with resultant radioresistance. Although having a low Hgb level has been shown to be detrimental, it is unclear as to exactly what the threshold should be for low Hgb (studies in this area have used thresholds ranging from 9-14.5 g/dL). Quality-of-life studies suggest that correction of moderately severe anemia may result in significant gains. Optimal Hgb levels for improving outcomes may vary across and within tumor types, and this is an area that requires further evaluation. However, the correction of anemia may be a worthwhile strategy for radiation oncologists to improve local control and survival. This article reviews the impact of anemia on outcomes after radiotherapy of head and neck cancers.

The effects of epoetin alfa on transfusion requirements in head and neck cancer patients: a prospective, randomized, placebo-controlled study

OBJECTIVE

To evaluate the efficacy of perioperative recombinant human erythropoietin (r-HuEPO, epoetin alfa) in stimulating hematopoiesis and reducing allogeneic blood transfusion requirements in major head and neck cancer surgery.

STUDY DESIGN

Double-blinded, placebo-controlled, randomized, prospective clinical trial.

METHODS

Fifty-eight patients undergoing surgical resection of head and neck tumors at the University of Iowa hospitals completed this study. Patients were required to have a pre-study hemoglobin >/=10.0 g/dL and </=13.5 g/dL. Group 1 (29 patients) received three doses of 600 IU/kg epoetin alfa before surgery. Group 2 (29 patients) received a placebo. All patients received oral iron supplementation (150 mg FeSO4 twice per day).

RESULTS

The epoetin alfa group demonstrated a significant increase in baseline to day-of-surgery mean hemoglobin (0.57 g/dL, P =.016), hematocrit (2.04%, P =.015), and reticulocyte count (95.3 x 103 cells/mm3, P = <.001), whereas there was no significant change in these hematologic variables in the placebo group. The percent of patients who avoided transfusion in the epoetin alfa group was 34.5% versus 17.2% in the placebo group. Patients requiring allogeneic blood transfusions received an average of 3.16 units in the epoetin alfa group and 4.12 units in the placebo group.

CONCLUSION

In this single institution study, we demonstrated a significant improvement in hematopoietic parameters and a trend toward decreased transfusion requirements using perioperative epoetin alfa in a head and neck cancer patient population. Further studies may delineate additional benefits in treating qualified patients with epoetin alfa during therapy for head and neck malignancies.

The negative impact of anemia on radiotherapy and chemoradiation outcomes

In cancer patients, anemia is common and has been found to impair quality of life and reduce locoregional disease control conferred by radiotherapy. The prognostic importance of anemia in the radiation oncology setting may be related to a reduction of molecular oxygen levels, thereby attenuating radiation-induced damage and ultimate cell death. Substantially higher doses of radiation are required to eradicate malignant cells under the hypoxic conditions commonly identified in solid tumors. Consistent with this, patients with hypoxic solid tumors have been found to have shorter postradiation disease-free survival rates relative to patients with well-oxygenated tumors. An attempt to enhance intratumoral oxygenation via correction of anemia, a highly prevalent but modifiable condition, is therefore a reasonable approach to optimize radiotherapy and chemoradiation outcomes. Clinical studies investigating recombinant human erythropoietin (epoetin alfa) as an adjunct to radiotherapy have demonstrated its ability to increase and maintain hemoglobin (Hb) levels during the course of radiotherapy. In a study involving anemic patients undergoing chemoradiation for head and neck cancer, epoetin alfa extended locoregional control and survival to rates reported for patients with normal pretreatment Hb levels. Given the high prevalence and prognostic significance of anemia during radiotherapy, strategies that safely and effectively increase Hb levels may be of value for optimizing radiotherapy and chemoradiation outcomes.

Anemia is associated with decreased survival and increased locoregional failure in patients with locally advanced head and neck carcinoma: a secondary analysis of RTOG 85-27

PURPOSE

The purpose of the present study is to investigate the strength of association between anemia and overall survival, locoregional failure, and late radiation therapy (RT) complications in a large prospective study of patients with advanced head and neck cancer treated with conventional radiotherapy with or without a hypoxic cell sensitizer.

METHODS AND MATERIALS

Between March 1988 and September 1991, 521 patients with Stage III or IV squamous cell carcinoma of the head and neck were entered into a randomized trial examining the addition of etanidazole (SR 2508) to conventional radiation therapy (RT) (66-74 Gy in 33-37 fractions, 5 days a week). Patients with hemoglobin (Hgb) levels measured and recorded prior to the second week of RT were included in this secondary analysis. Hemoglobin levels were stratified as normal (> or = 14.5 gm% for men, > or = 13 gm% for women) or anemic (< 14.5 gm% for men, < 13 gm% for women). Locoregional failure rates were calculated using the cumulative incidence approach. Overall survival was estimated according to the Kaplan-Meier method. Late RT toxicity was scored according to the RTOG morbidity scale. Differences in rates of overall survival, locoregional failure, and late complications were tested by the Cox proportional hazard model.

RESULTS

Of 504 eligible patients, 451 had a Hgb level measured and recorded prior to the second week of RT. One hundred sixty-two patients (35.9%) were considered to have a normal Hgb level and 289 patients (64.1%) were considered to be anemic. The estimated survival rate is 35.7% at 5 years in patients with a normal Hgb, versus 21.7% in anemic patients (p = 0.0016). The estimated locoregional failure rate is 51.6% at 5 years in patients with a normal Hgb, versus 67.8% in anemic patients (p = 0.00028). The estimated rate of grade 3 or greater toxicity is 19.8% at 5 years in patients with a normal Hgb, versus 12.7% in anemic patients (p = 0.063). On multivariate analysis, several variables were found to be independent predictors of survival including: T stage, Karnofsky performance status, N stage, age, total radiation dose to the primary, and Hgb level. Independent predictors of locoregional control included T stage, Karnofsky performance status, N stage, radiation dose, and Hgb level. The only variables which predicted for the development of late RT complications were gender (p = 0.0109) and age (p = 0.0167). These findings were consistent regardless of whether Hgb level was considered a dichotomous or continuous variable.

CONCLUSION

Low Hgb levels are associated with a statistically significant reduction in survival and an increase in locoregional failure in this large prospective study of patients with advanced head and neck cancer. Hgb level should be considered as a stratification variable in subsequent studies of head and neck cancer. Strategies to increase Hgb prior to RT in patients with head and neck cancer may lead to improved survival and loco-regional control.

A randomized double-blind phase III study of nimorazole as a hypoxic radiosensitizer of primary radiotherapy in supraglottic larynx and pharynx carcinoma. Results of the Danish Head and Neck Cancer Study (DAHANCA) Protocol 5-85

PURPOSE

A multicenter randomized and balanced double-blind trial with the objective of assessing the efficacy and tolerance of nimorazole given as a hypoxic radiosensitizer in conjunction with primary radiotherapy of invasive carcinoma of the supraglottic larynx and pharynx.

PATIENTS AND TREATMENT

Between January 1986 and September 1990, 422 patients (414 eligible) with pharynx and supraglottic larynx carcinoma were double-blind randomized to receive the hypoxic cell radiosensitizer nimorazole, or placebo, in association with conventional primary radiotherapy (62-68 Gy, 2 Gy per fraction, five fractions per week). The median observation time was 112 months.

RESULTS

Univariate analysis showed that the outcome (5-year actuarial loco-regional tumor control) was significantly related to T-classification (T1-T2 48% versus T3-T4 36%, P = 0.0008), neck-nodes (N- 53% versus N+ 33%), pre-irradiation hemoglobin (Hb) concentration (high 46% versus low 37%, P = 0.02) and sex (females 51% versus males 38%, P = 0.03). Overall the nimorazole group showed a significantly better loco-regional control rate than the placebo group (49 versus 33%, P = 0.002). A similar significant benefit of nimorazole was observed for the end-points of final loco-regional control (including surgical salvage) and cancer-related deaths (52 versus 41%, P = 0.002). This trend was also found in the overall survival but to a lesser, non-significant extent (26 versus 16%, 10-year actuarial values, P = 0.32). Cox multivariate regression analysis showed the most important prognostic parameters for loco-regional control to be positive neck nodes (relative risk 1.84 (1.38-2.45)), T3-T4 tumor (relative risk 1.65 (1.25-2.17)) and nimorazole (relative risk 0.69 (0.52-0.90)). The same parameters were also significantly related to the probability of dying from cancer. The compliance to radiotherapy was good and 98% of the patients received the planned dose. Late radiation-related morbidity was observed in 10% of the patients, irrespective of nimorazole treatment. Drug-related side-effects were minor and tolerable with transient nausea and vomiting being the most frequent complications.

CONCLUSION

Nimorazole significantly improves the effect of radiotherapeutic management of supraglottic and pharynx tumors and can be given without major side-effects.

Prognostic value of hemoglobin concentration in radiotherapy for cancer of supraglottic larynx

PURPOSE

The aim of this work is the estimation of correlations between hemoglobin concentration either before or after radiotherapy and local tumor control probability for laryngeal cancer.

METHODS AND MATERIALS

Retrospective analysis of 847 cases of laryngeal supraglottic squamous cell carcinoma treated with radiation alone was performed using maximum likelihood estimations, and step-wise logistic regression. All patients were in good initial performance status (Karnofsky index >70). The minimum follow-up time was 3 years.

RESULTS

Logistic regression showed that the hemoglobin concentration after radiotherapy is an important prognostic factor. There was a very strong correlation between hemoglobin concentration and tumor local control probability. Hemoglobin concentration at the beginning of radiotherapy does not correlate with treatment outcome, but any decrease of hemoglobin during therapy is a strong prognostic factor for treatment failure.

CONCLUSIONS

Although regression models with many variables may be instable, the present results suggest that hemoglobin concentration after treatment is at least as important as overall treatment time. It was not possible to find out whether the low concentration of hemoglobin is an independent cause of low TCP or whether it reflects other mechanisms that may influence both hemoglobin level and the TCP.

Treatment results of nasopharyngeal cancer--a nationwide survey from Finland

The nationwide experience of treating nasopharyngeal cancer in Finland during the period 1980-1989 was reviewed. Of the 107 patients included in the present analysis, 13 were treated palliatively only, and three had metastatic disease at their first clinical presentation, whereas the rest (n = 91) were treated with radical radiotherapy, of whom, 8 patients received adjuvant chemotherapy after radiotherapy. The 5-year actuarial survival rates of these 91 patients was 52%, and by the UICC stage they were classified as follows: stage I 75% (n = 12), stage II 60% (n = 5), stage III 59% (n = 34), and stage IV 38% (n = 40). According to the Cox's stepwise proportional hazard model the most important factors influencing favourable survival were the total dose of radiotherapy expressed in terms of Biologically Effective Dose (BED) with a time factor, a small size of the primary tumour and a high performance status according to the WHO scale, whereas the most important factors influencing the local control analysis were the total dose of radiotherapy (expressed in BED) and the cervical lymph node status.

Effect of subcutaneous recombinant human erythropoietin in cancer patients receiving radiotherapy: preliminary results of a randomized, open-labeled, phase II trial

PURPOSE

To determine the efficacy and safety of subcutaneous administration of recombinant human erythropoietin (r-HuEPO) at a dose of 200 units/kg/day to cancer patients undergoing radiotherapy.

METHODS AND MATERIALS

This is a randomized, open-labeled, Phase II study. Only patients receiving radiotherapy +/- chemotherapy are included. Eligibility is restricted to patients with lung cancer, carcinoma of the uterine cervix, prostatic adenocarcinoma, or adenocarcinoma of the breast. Patients in the control and treatment arms receive radiotherapy with similar policies, and their doses of radiotherapy and treatment volumes are determined by the site and stage of the disease. Patients in the "treatment arm" receive 200 units/kg/day of r-HuEPO, subcutaneously, five times a week with iron (Fe SO4, 325 mg. p.o., t.i.d.) supplements. Complete blood counts are obtained weekly. Quality of life is assessed weekly by the patients themselves by a few simple entries on an analog scale.

RESULTS

Twenty-six patients have been entered in the study so far. Twelve patients were placed in the control arm and 14 in the treatment arm. Pre-randomization demographic and laboratory mean values in both arms were comparable, with none of 16 parameters compared reaching statistical significance. Our results can be summarized as follows: (a) Mean hemoglobin, hematocrit, and red blood cell values increased gradually in the treatment arm patients. Week-by-week comparison showed that mean values for these three parameters were significantly higher in the treatment arm than in the control arm. For example, the p values for the differences in hemoglobin mean values for weeks 1-6 were 0.015, 0.002, 0.003, 0.0002, 0.0006, and 0.007, respectively. Similar trends were observed for red blood cells and the hematocrit values. (b) No significant toxicity has been encountered. (c) No significant differences in the mean values of white blood cells and platelet counts were seen between the two arms. The values of these two parameters declined over the course of radiotherapy. (d) The mean weekly increase in hemoglobin levels in the treatment arm was 0.43 gm/dl.

CONCLUSION

(a) The safety and efficacy of r-HuEPO, with 200 units/kg/day of subcutaneous administration, have been confirmed in our study group. (b) However, the rate of increase in hemoglobin levels is not very rapid with the doses used. (c) Dose escalation studies are needed for determination of the feasibility of improving hemoglobin levels by about 1 gm/dl/week. (d) The question whether improvement in hemoglobin with r-HuEPO therapy can improve outcome by improving tumor oxygenation needs to be studied in carcinoma of the uterine cervix and squamous cell carcinoma of the head and neck.

The prognostic value of hemoglobin and a decrease in hemoglobin during radiotherapy in laryngeal carcinoma

An association between a low Hb-content and a poor response on radiation therapy has been established in previous years, especially in patients with squamous cell carcinomas. Whether this is linked with hypoxic conditions of the tumour or associated with tumour volume, blood loss or other conditions, is not yet known for certain. Patients with small head and neck tumours seem to form an interesting group to study this issue because several factors can be ruled out. Therefore, a retrospective analysis of 306 patients with glottic or supraglottic carcinoma was performed, to identify whether the Hb-value was of prognostic importance and whether this was linked to other patient characteristics. All patients were treated with primary radiotherapy with doses ranging from 60 to 70 Gy in 6-7 weeks. It appeared that in glottic carcinoma, the disease-free survival was significantly worse in patients with a Hb-value below normal at the start or/and at the end of therapy (p = 0.09, p = 0.0012, respectively). In patients with supraglottic carcinoma, the above mentioned difference approved only for a Hb-value below normal at the end of treatment (p = 0.05). A decrease in Hb-level of greater than or equal to 0.5 mmol/l during therapy, regardless whether the Hb-values were within or beyond normal range, reduced the disease-free survival in patients with glottic carcinoma (p = 0.0125). In a multivariate analysis, the Hb-value at the end of treatment proved to be an independent prognostic factor after T- and N-classification. There was no relationship with nutritional condition of the patient, nor with the Karnofsky Performance scale.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical radiobiology of squamous cell carcinoma of the oropharynx

Local tumor control is analyzed in a series of 181 patients treated with definitive megavoltage radiotherapy (RT) for histologically proven squamous cell carcinoma of the oropharynx. Considerable variation in treatment time stemmed from the general use of a split-course technique in 49 patients treated from 1978 to 1985. Incomplete follow-up, in those patients alive and well at the termination of the study or who have died from metastases or intercurrent disease before developing a local recurrence, was allowed for by using a multi-variate mixture model. The tumor control probability (TCP) after radiotherapy showed a significant dependence on the following tumor and treatment characteristics: (a) tumor size: the number of tumor target cells increases approximately as the fourth root of estimated tumor volume; (b) sex: the estimated TCP in males is lower than in females with the same characteristics; (c) histopathological differentiation: well-differentiated tumors have a lower TCP than poorly and intermediately differentiated; (d) hemoglobin concentration: patients in the upper normal range have a significantly higher TCP than others; (e) total dose: there is a significant dose-response relationship; and (f) overall treatment time: TCP decreased with increasing overall time, the dose equivalent of proliferation with 2 Gy per fraction was 0.68 Gy/day with 95% confidence limits [0.05, 1.3] Gy/day. The TCP did not depend significantly on subsite within the oropharynx or nodal disease at presentation. The data were consistent with an alpha/beta ratio of the linear-quadratic model of 10 Gy.

The influence of chronic anaemia on the radiosensitivity of two mouse tumours

There is clear clinical evidence that tumours in anaemic patients are difficult to control with radiotherapy. We have studied the radiosensitivity of two transplantable mouse tumours, the SCCVII/St carcinoma and the KHT sarcoma in hosts made anaemic either with an iron poor diet or as a result of tumour growth. The haemoglobin level and haematocrits of mice on the low iron diet fell to about 60% of normal within 11 weeks. The number of clonogenic cells after a single X-ray dose of 20 Gy was slightly lower (P less than 0.05) in the anaemic animals (2.3 X 10(4) g-1) than in controls (5.2 X 10(4) g-1) though there was no significant difference in the surviving fractions. Mice bearing KHT tumours became anaemic with haematocrits falling to 65% of normal as their tumours grew from 300-1200 mg. A second 'test' tumour was implanted one week after the first 'anaemia-inducing' tumour so that estimates of radiosensitivity could all be carried out on tumours within the same size range (150-300 mg). Radiosensitivity was significantly greater in the most anaemic hosts with 2.2 X 10(4) cells g-1 surviving a dose of 20 Gy compared with 6.7 x 10(4) g-1 in controls (P less than 0.01). These results are consistent with most published data for mouse tumours though not for many human tumours.