Low oxygen level prostate tumors often recurrent
Last Updated: 2009-05-29 16:46:43 -0400 (Reuters Health)
June 1, 2009
By Megan Rauscher
NEW YORK (Reuters Health) - Hypoxia, or reduced oxygen levels, in prostate tumors significantly predicts a poor long-term biochemical outcome, regardless of other prognostic factors, such as tumor stage or type, according to results of a study presented at the American Society of Clinical Oncology's annual meeting in Orlando.
The finding, Benjamin Movsas told Reuters Health, suggests that new hypoxic strategies should be investigated. Patients with prostate cancer who have low tumor oxygen levels may response to combination treatment with radiation therapy and other strategies such as angiogenesis, the formation of new blood vessels that tumors need to grow.
"Most patients with localized prostate cancer do extremely well whether they are treated with surgery or with radiation, but there is a small number of patients -- maybe 10 percent or so - (who) do not do as well, and the question is why," Movsas noted.
To see if tumor oxygenation, which is critical to the successful treatment of many cancers, played a role, Movsas and colleagues studied 57 patients with localized prostate cancer. They used custom-made microelectrode oxygen probes to obtain a total of 11,516 oxygen measurements from the prostate, focusing on positive biopsy locations, with normal muscle tissue as a control.
Measurements were obtained immediately before prostate brachytherapy, placement of radioactive "seeds" placed in the tumor that slowly but continually release radiation.
"We have followed the patients now for 8 years and it turns out that the patients who had low prostate tumor oxygen levels had much worse outcomes and much more biochemical failures than patients who had normal or higher levels of oxygen in their tumors," Movsas said.
During follow-up, there were 12 biochemical failures using the ASTRO definition (i.e. three consecutive increases in prostate-specific antigen levels (PSA), a biologic marker of prostate cancer, and 8 biochemical failures using the by the Phoenix, or Nadir+2, definition (i.e., an increase of at least 2 ng/mL from the lowest PSA reading).
Upon further analysis, a low ratio of prostate tumor oxygen to muscle oxygen levels (less then 0.10, versus 0.10 or greater) was a significant predictor of biochemical failure by both the ASTRO and Phoenix definitions.
By the ASTRO definition, 46 percent of patients with low tumor oxygen levels were free of biochemical failure at 8 years versus 78 percent of patients with higher oxygen levels. Using the Phoenix definition, the corresponding rates of freedom from biochemical failure were 66 percent versus 89 percent.
Summing up, Movsas said: "We need to do better in terms of identifying which patients need more that the standard therapies. We want to study tumor oxygenation further and start applying newer noninvasive approaches to determining tumor oxygen levels, so we could apply this to more patients. Once patients with low oxygen levels are identified, they could be candidates for angiogenesis therapies."