Anemia, tumor hypoxemia, and the cancer patient.

OBJECTIVE

To review the impact of anemia/tumor hypoxemia on the quality of life and survival in cancer patients, and to assess the problems associated with the correction of this difficulty.

METHODS

MEDLINE searches were performed to find relevant literature regarding anemia and/or tumor hypoxia in cancer patients. Articles were evaluated in order to assess the epidemiology, adverse patient effects, anemia correction guidelines, and mechanisms of hypoxia-induced cancer cell growth and/or therapeutic resistance. Past and current clinical studies of radiosensitization via tumor oxygenation/hypoxic cell sensitization were reviewed. All clinical studies using multi-variate analysis were analyzed to show whether or not anemia and/or tumor hypoxemia affected tumor control and patient survival. Articles dealing with the correction of anemia via transfusion and/or erythropoietin were reviewed in order to show the impact of the rectification on the quality of life and survival of cancer patients.

RESULTS

Approximately 40-64% of patients presenting for cancer therapy are anemic. The rate of anemia rises with the use of chemotherapy, radiotherapy, and hormonal therapy for prostate cancer. Anemia is associated with reductions both in quality of life and survival. Tumor hypoxemia has been hypothesized to lead to tumor growth and resistance to therapy because it leads to angiogenesis, genetic mutations, resistance to apoptosis, and a resistance to free radicals from chemotherapy and radiotherapy. Nineteen clinical studies of anemia and eight clinical studies of tumor hypoxemia were found that used multi-variate analysis to determine the effect of these conditions on the local control and/or survival of cancer patients. Despite differing definitions of anemia and hypoxemia, all studies have shown a correlation between low hemoglobin levels and/or higher amounts of tumor hypoxia with poorer prognosis. Radiosensitization through improvements in tumor oxygenation/hypoxic cell sensitization has met with limited success via the use of hyperbaric oxygen, electron-affinic radiosensitizers, and mitomycin. Improvements in tumor oxygenation via the use of carbogen and nicotinamide, RSR13, and tirapazamine have shown promising clinical results and are all currently being tested in Phase III trials. The National Comprehensive Cancer Network (NCCN) guidelines recommend transfusion or erythropoietin for symptomatic patients with a hemoglobin of 10-11 g/dl and state that erythropoietin should strongly be considered if hemoglobin falls to less than 10 g/dl. These recommendations were based on studies that revealed an improvement in the quality of life of cancer patients, but not patient survival with anemia correction. Phase III studies evaluating the correction of anemia via erythropoietin have shown mixed results with some studies reporting a decrease in patient survival despite an improvement in hemoglobin levels. Diverse functions of erythropoietin are reviewed, including its potential to inhibit apoptosis via the JAK2/STAT5/BCL-X pathway. Correction of anemia by the use of blood transfusions has also shown a decrement in patient survival, possibly through inflammatory and/or immunosuppressive pathways.

CONCLUSIONS

Anemia is a prevalent condition associated with cancer and its therapies. Proper Phase III trials are necessary to find the best way to correct anemia for specific patients. Future studies of erythropoietin must evaluate the possible anti-apoptotic effects by directly assessing the tumor for erythropoietin receptors or the presence of the JAK2/STAT5/BCL-X pathway. Due to the ability of transfusions to cause immunosuppression, most probably through inflammatory pathways, it may be best to study the effects of transfusion with the prolonged use of anti-inflammatory medications.