Mitomycins: A group of methylazirinopyrroloindolediones obtained from certain Streptomyces strains. They are very toxic antibiotics used as ANTINEOPLASTIC AGENTS in some solid tumors. PORFIROMYCIN and MITOMYCIN are the most useful members of the group.Porfiromycin: Toxic antibiotic of the mitomycin group, obtained from MITOMYCIN and also from Streptomyces ardus and other species. It is proposed as an antineoplastic agent, with some antibiotic properties.Mitomycin: An antineoplastic antibiotic produced by Streptomyces caespitosus. It is one of the bi- or tri-functional ALKYLATING AGENTS causing cross-linking of DNA and inhibition of DNA synthesis.