To future investigate the potential link between the caspase family activation and the antitumor activity of HMME-PDT, immunohistochemistry (IHC) was employed to measure the relative expression of caspase-1, caspase-3, caspase-6, caspase-9, and PARP proteins; the results showed these proteins were primarily expressed in the cytoplasm of tumor tissue. Here, CASP6 is linked to neoplasm.