Four mitochondrial genes (COI, ATP8, ND1, and ND3) were analyzed in GC (AGP01, ACP02, ACP03, and PG100) and control (Walker 256 carcinosarcoma) cell lines inoculated in Sapajus apella, exposed and not exposed to N‐methyl‐N‐nitrosourea. The gene discussed is MT-ND3; the disease is carcinosarcoma.