Decreased tumor oxygenation after cyclophosphamide, reoxygenation and therapeutic enhancement with a perflubron emulsion carbogen breathing

Thermochemoradiotherapy Improves Oxygenation in Locally Advanced Breast Cancer

PURPOSE

The purpose of this research was to evaluate toxicity, response, and changes in oxygenation (pO(2)) in patients with locally advanced breast cancer (LABC) treated with concurrent taxol, hyperthermia (HT), and radiation therapy (RT) followed by mastectomy.

EXPERIMENTAL DESIGN

Eighteen patients with LABC were enrolled from October 1995 through February 1999. Treatment consisted of taxol (175 mg/m(2)) given every 3 weeks for three cycles. Radiation therapy included the breast and regional nodes with a dose of 50 Gy, followed by a boost to 60-65 Gy for those not undergoing surgery. Mastectomy was performed for patients deemed resectable after this neoadjuvant program. HT was administered twice per week. Oxygenation was measured before the first HT treatment and 24 h after the first HT treatment.

RESULTS

Fifteen of 18 patients responded, 6 with a clinical complete response, 9 with a partial clinical response, and 3 nonresponders. Thirteen underwent mastectomy with 3 pathological complete responses. Tumor hypoxia was present in 8 of 13 patients (pO(2) = 4.7 +/- 1.2 mmHg). Five patients had well-oxygenated tumors (pO(2) = 27.6 +/- 7.8 mmHg). Patients with well-oxygenated tumors before treatment as well as those with significant reoxygenation had a favorable clinical response. Tumor reoxygenation appeared to be temperature dependent and associated with the lower thermal doses.

CONCLUSIONS

This novel therapeutic program resulted in a high response rate in patients with LABC. Hyperthermia may offer a strategy for improving tumor reoxygenation with consequent treatment response. However, the effect of hyperthermia on tumor reoxygenation appears to depend on thermal dose and requires additional investigation.

Hypoxia and drug resistance

Biologically and therapeutically important hypoxia occurs in many solid tumor masses. Hypoxia can be a direct cause of therapeutic resistance because some drugs and radiation require oxygen to be maximally cytotoxic. Cellular metabolism is altered under hypoxic conditions. Hypoxia can result in drug resistance indirectly if under this condition cells more effectively detoxify the drug molecules. Finally, there is evidence that hypoxia can enhance genetic instability in tumor cells thus allowing more rapid development of drug resistance cells. The current review describes the effects of hypoxia on tumor response to a variety of anti-cancer agents and also describes progress toward therapeutically useful methods of delivering oxygen to tumors in an effort to overcome therapeutic resistance due to hypoxia. Finally, the use of hypoxic cell selective cytotoxic agents as a means of addressing hypoxic 'drug resistance' is discussed.