In cancer cells exposed to an overdose of 5-ALA, the downregulation of ferrochelatase (FECH) halts the conversion of PPIX to heme in the mitochondria, leading to an overaccumulation of intracellular PPIX [14,15], which is a photosensitizer that emits red fluorescence when exposed to light wavelengths of 430–435 nm [16,17]. Here, FECH is linked to cancer.