Oxygen distributions partly explain the radiation response of human squamous cell carcinomas

The oxygen tension of human tumours has often been thought to alter tumour response to radiation therapy. The purpose of this analysis is to determine to what extent the observed results of radiotherapy fit predictions based on in situ human tumour pO2 distributions. The radiation dose-response curve for patients treated with radiation alone for squamous cell cancers of the cervix and oropharynx were calculated based on published data. pO2 histograms were obtained from 30 women with cervical cancer and 11 patients with neck nodes from head and neck cancers. An average of 76 +/- 35 (range 28-174) measurements were made from each patient. Hypoxia was assumed to be a purely dose-modifying factor with a maximum OER of 2.5. Assuming patients are treated with daily radiation doses of 2 Gy, the squamous cell carcinoma alpha/beta ratio is 10 Gy, and that tumours have a mean of 10(8) clonogens, it was possible to estimate tumour control probability. Tumour oxygenation was an extremely important modifier of the slope of the dose-response curve and alone was sufficient to account for the slope of the clinically observed dose-response curve for neck nodes. The response curve for uterine cervical cancers is very shallow, and the oxygen distribution did not completely account for heterogeneity of response of these tumours. The results support the conclusion that oxygen tension distribution is an important modifier of human radiation treatment response.

Oxygen tension measurements of head and neck cancers

OBJECTIVE

There is continued investigation of agents capable of overcoming hypoxic cell radioresistance. The evaluation of tumor oxygenation, therefore, assumes great importance. Previous efforts to measure tumor oxygen tension (PO2) using polarographic methods were limited by the size of the electrodes and efficiency of measurements. A new system employing fine-needle electrodes and a computerized micromanipulator was evaluated.

DESIGN

Prospective study.

PATIENTS

Sixteen patients with cancers of the head and neck, seen at Stanford (Calif) University Medical Center and Santa Clara Valley Medical Center, San Jose, Calif, between March 1, 1991, and July 31, 1991. Of the 16 tumors, 14 were squamous cell carcinomas; 11 were previously untreated. In two patients, measurements were repeated during radiation therapy. In three patients, measurements were taken under conditions of varied inspired oxygen during anesthesia. In seven patients, subcutaneous tissue (SQ) measurements were made for comparison.

RESULTS

The mean (+/- SD) PO2 of all tumors was 25.6 +/- 20.2 mm Hg, with a range of 2.3 to 76.4 mm Hg. When only squamous cell carcinomas were considered, the mean tumor PO2 was 22.7 +/- 16.0 mm Hg. The mean SQ measurement was 57.2 +/- 12.8 mm Hg. In all cases (seven of seven) in which SQ data were available, the tumor PO2 was lower than the SQ PO2 by an average of 41.8 mm Hg. The mean tumor PO2 increased in two of three cases of hyperoxia and decreased in the the third. The mean tumor PO2 increased in one patient after 25 Gy of radiotherapy and remained the same in the other.

CONCLUSIONS

These measurements suggest that there is significant interindividual variability in the PO2 of head and neck cancers. Squamous cell cancers are generally less well oxygenated than normal SQ tissue. The PO2 histograph identified patients with a low mean tumor PO2.

Oxygen tension distributions are sufficient to explain the local response of human breast tumors treated with radiation alone

PURPOSE

Several factors are known to influence the probability of tumor control after radiation. These include tumor oxygen tension distribution, glutathione content, intrinsic radiation sensitivity, rate of repopulation, tumor size, physician skill, etc. The relative impact of oxygen on human tumor response is unknown. The purpose of this analysis is to determine to what extent the observed shape of the radiation response curve for human tumors can be predicted by the tumor oxygenation status.

METHODS AND MATERIALS

The radiation dose response curve for patients treated with radiation alone for breast cancer was calculated based on pooled data. Tumor control rates as a function of radiation dose were fitted to a probit curve. Twenty-two women with breast cancer in Mainz (Germany) and at Stanford University had pO2 measurements made of their tumors. An average of 87 +/- 58 (range 21 to 300) measurements were made from each patient. Hypoxia was assumed to be a purely dose modifying factor with a maximum oxygen enhancement ratio of 2.5. Assuming patients are treated with daily radiation doses of 2 Gy, the breast cancer alpha/beta ratio is 10 Gy, tumors have a mean of 10(8) stem cells, and using the linear quadratic formula for modelling surviving fraction, it was possible to estimate tumor control probability.

RESULTS

Tumor oxygenation was an extremely important modifier of the shape of the dose response curve and alone was sufficient to account for the slope of the observed dose response curve for human breast carcinoma. Tumor size distribution had a smaller effect on the shape and the slope of the dose response curve. Two models of radiation induced reoxygenation were tested, one that allowed full reoxygenation to the baseline state between the daily radiation fractions and another with no reoxygenation between fractions. The clinical data fell between these two models in accordance with the expected incomplete reoxygenation between treatments.

CONCLUSION

The results support the conclusion that in human breast carcinoma, oxygen tension distribution is a critical modifier of radiation treatment response.

Computerized histographic oxygen tension measurements of murine tumors

As further work on tumor oxygenation results in the development of agents capable of modulating hypoxic cell radiosensitivity, and chemotherapeutic agents capable of targeting hypoxic cells, knowledge of relative tumor oxygenation takes on greater importance. The pO2 Histograph was used to characterize the oxygen tension of a murine sarcoma (RIF1) and a murine carcinoma (SCCVII), each with different hypoxic fractions. These tumors were studied sequentially to assess the suitability of the Histograph both as a research tool and, ultimately, as a clinical monitor of tumor hypoxia.

The influence of initial hemoglobin and blood pressure levels on results of radiation therapy for carcinoma of the prostate

A group of 914 patients with carcinoma of the prostate treated by definitive radiotherapy at Stanford between 1956 and 1985 was studied. Of these, the initial hemoglobin level was recorded in 656 cases and the initial blood pressure in 760 cases. End-points studied in actuarial analyses were survival, disease-specific survival, local control, freedom from distant relapse, and occurrence of late intestinal complications. Although the anemic group (Hb less than 13.5 g/dl) was correlated negatively with survival (p = 0.02), there was no correlation with disease-specific survival or local control. The conclusion was that anemia per se did not affect the outcome of radiation therapy. A pulse pressure greater than or equal to 60 mm Hg was significantly correlated with worse survival (p = 0.01) and local control (p = 0.04), but no correlation was found between systolic and diastolic blood pressure and the end-points measured. Neither anemia nor hypertension were significantly correlated with late intestinal complications.

Radiotherapy employing three fractions on each of twelve consecutive days

In order to achieve the greatest advantage of accelerated hyperfractionated radiotherapy, treatment has been given 3 times each day for 12 consecutive days without a rest period. A total tumour dose of 50.4 Gy was well tolerated in a series of 38 patients with bronchial, head and neck and oesophageal carcinomas. A further 14 patients have now received an elevated dose of 54 Gy, again with satisfactory tolerance. The tumour responses at all these sites have been very promising and further work is proceeding.

A comparative study of Ro 03-8799: racemic mixture and enantiomers

The maximum single dose of the 2-nitroimidazole hypoxic cell radiosensitiser Ro 03-8799 is limited to 1 g/m2 by the occurrence of a well characterised acute syndrome of sweating, nausea and mental changes. In an attempt to increase the tolerable dose, the clinical toxicity of the racemic mixture was compared with that of the R- and S-enantiomers of Ro 03-8799. Twelve patients received escalating alternate doses of racemic mixture and R- or S-enantiomer, the dose levels being 0.25 g/m2, 0.5 g/m2, 0.75 g/m2 and 1.0 g/m2. Careful monitoring of the acute syndrome failed to demonstrate any consistent differences between racemic mixture and either enantiomer. This would suggest that the toxicity is not mediated via any specific central nervous system receptor. It is concluded that separation of Ro 03-8799 into its enantiomers will not enable a clinically useful increase in dosage.

A comparison of the tumour concentrations obtainable with misonidazole and Ro 03-8799

Both Ro 03-8799 and misonidazole were administered to six patients before tumour sampling. Using similar doses, tumour concentrations of Ro 03-8799 were approximately double those of misonidazole. Examination of the data with regard to the relative sensitising efficiencies of these two compounds gives us, as a conservative estimate, a factor of 1.6 in favour of Ro 03-8799. From these observations it is predicted that, when given with radiotherapy in a 25-fraction course Ro 03-8799, is likely to be at least five times more effective as a hypoxic cell sensitiser than misonidazole.

Concentrations achieved in human tumors after administration of misonidazole, SR-2508 and Ro 03-8799

Misonidazole, SR-2508 and Ro 03-8799 have been given in sequence to patients before tumor sampling. Tumor concentrations of the three drugs have been measured and it has been possible to make prediction as to the likely advantage of the newer drugs over misonidazole. Based upon the three cases described here and 13 others given two drug combination, we suggest that in multifraction radiotherapy, both are likely to prove more than five times more efficient than misonidazole.

Crohn's disease limited to the mouth and anus

A young girl developed painful swelling and ulceration of her lips and mouth. She had gingival hyperplasia, an anal fissure, and anal skin tags without evidence of intervening intestinal disease. A diagnosis of Crohn's disease was made. All lesions regressed with appropriate therapy. She remains asymptomatic 14 months after presentation.