Culture media of MCF-7 breast cancer cells were subjected to solid-phase Porapak Q extraction. Ten-fold diluted extracts with methanol were injected to LC-TOF/MS. Targeted m/z values for 5-(Z)-dodecenoic acid and related-unsaturated fatty acids for EIC-LC-TOF/MS analysis were as follows: (a) C10:1 ([M-H]- = 169.1223 m/z), (b) C10:2 ([M-H]- = 167.1067 m/z), (c) C12:1 [5-(Z)-dodecenoic acid: [M-H]- = 197.1536 m/z], (d) C14:1 [5-(Z)-tetradecenoic acid: [M-H]- = 225.1849 m/z], (e) C14:2 ([M-H]- = 223.1693 m/z), (f) C16:2 ([M-H]- = 251.2006 m/z), and (g) C18:2 (linoleic acid: [M-H]- = 279.2319 m/z). EIC-MS chromatograms obtained from the extracts of breast cancer MCF-7 and fibroblast KMST-6 cells were in orange and black colour, respectively. Analytical conditions for LC-TOF/MS on a Cosmosil 5C18-MS-II column (2.0 mm × 150 mm) were described in the Methods section.