Increased singlet oxygen-induced secondary ROS production in the serum of cancer patients

Photodynamic therapy (PDT) generates singlet oxygen (1O2) and Reactive Oxygen Species (ROS) that are counteracted by patient’s defenses. As cancer treatments are among the most important PDT applications the aim of this pilot study was to determine whether the serum of cancer patients produces more or less secondary ROS or peroxides after a photoreaction as compared to healthy persons. Fifty-three volunteers and 105 cancer patients were recruited. The capacity of 1O2 or secondary oxidant production was found to be increased in 6 healthy donors and 36 cancer patients (23/69 women and 13/31 men p < 0.007 and p < 0.04) with a mean value of 1.52 as compared to 1.29 in the healthy subjects (p < 0.05) when considering values higher than the normal range (norm = 1 ± 10%) or 1.1 vs. 0.85 (p < 0.01) in the whole cohort. This increase correlated with a poor prognosis, TNM and SBR classification. Serum 1O2 deactivation capacity was impaired and secondary ROS were more produced during cancer progression. Although it is currently unclear whether this is the cause or effect of cancer, this finding may hold interest as a potential marker of cancer severity. It would also support the interest of PDT as an adjuvant for cancer treatment, even for aggressive tumors particularly when associated to surgery for bulk removal.