The management of programmed cell death-sensitive human epidermoid carcinoma cells (A431) with PDT provoked a relevant increase in clusterin with a peak at 12 h after treatment, while the clusterin concentrations in Pc 4-PDT-treated, apoptosis-resistant, radiation-induced fibrosarcoma (RIF-1) cells remained unaffected. This evidence concerns the gene CLU and squamous cell carcinoma.