GSTM1 and neoplasm: One tumor was treated with high-dose ALA-PDT and showed a limited modification of Hb-pO2 in the first 24 hrs (Atif et al., 2021), whereas for two ALA- and BPD-mediated PDT-subjected tumors, Hb-pO2 started dropping immediately post-PDT and was less than 30% after 4 hrs until 24 hrs post-PDT, as expected.